DS2784G [MAXIM]

1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication; 1 ,电池的独立式电量计IC,带有Li +电池保护和SHA -1认证
DS2784G
型号: DS2784G
厂家: MAXIM INTEGRATED PRODUCTS    MAXIM INTEGRATED PRODUCTS
描述:

1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
1 ,电池的独立式电量计IC,带有Li +电池保护和SHA -1认证

电池 仪表
文件: 总43页 (文件大小:607K)
中文:  中文翻译
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19-4636; Rev 3/12  
DS2784  
1-Cell Stand-Alone Fuel Gauge IC with  
Li+ Protector and SHA-1 Authentication  
GENERAL DESCRIPTION  
FEATURES  
. Precision Voltage, Temperature, and Current  
The DS2784 operates from 2.5V to 4.6V for integration  
in battery packs using a single lithium-ion (Li+) or Li+  
polymer cell. Available capacity is reported in mAh and  
as a percentage. Safe operation is ensured with the  
included Li+ protection function and SHA-1-based  
challenge-response authentication.  
Measurement System  
. Available Capacity Estimated from Coulomb  
Count, Discharge Rate, Temperature, and Cell  
Characteristics  
. Estimates Cell Aging Using Learn Cycles  
. Uses Low-Cost Sense Resistor  
Precision measurements of voltage, temperature, and  
current, along with cell characteristics and application  
parameters are used to estimate capacity. The  
available capacity registers report a conservative  
estimate of the amount of charge that can be removed  
given the current temperature and discharge rate.  
. Allows for Calibration of Gain and  
Temperature Coefficient  
. Li+ Safety Circuitry—Overvoltage,  
Undervoltage, Overcurrent, Short-Circuit  
Protection  
. Programmable Safety Thresholds for  
In addition to the nonvolatile (NV) storage for cell  
compensation and application parameters, 16 bytes of  
EEPROM memory is made available for the exclusive  
use of the host system and/or pack manufacturer. This  
facilitates battery lot and date tracking or NV storage of  
system or battery usage statistics.  
Overvoltage and Overcurrent  
. Authentication Using SHA-1 Algorithm and  
64-Bit Secret  
. 32-Byte Parameter EEPROM  
. 16-Byte User EEPROM  
A 1-Wire® interface provides serial communication at  
16kbps or 143kbps to access data registers, control  
registers, and user memory. Additionally, 1-Wire  
communication enables challenge-response pack  
authentication using SHA-1 as the hash algorithm in a  
hash-based message authentication code (HMAC)  
authentication protocol.  
. Maxim 1-Wire Interface with 64-Bit Unique ID  
. Tiny, Pb-Free, 14-Pin TDFN Package Embeds  
Easily in Battery Packs Using Thin Prismatic  
Cells  
PIN CONFIGURATION  
VDD  
CTG  
VSS  
VIN  
NC  
PIO  
CP  
APPLICATIONS  
Smartphones/PDAs  
Digital Still and Video Cameras  
Cordless VoIP Phones  
Portable GPS Navigation  
SNS  
DQ  
NC  
NC  
DC  
PAD  
PLS  
CC  
3mm x 5mm TDFN – 14  
Top View  
Modes and commands are capitalized for clarity.  
1-Wire is a registered trademark of Maxim Integrated Products, Inc.  
ORDERING INFORMATION  
PART  
DS2784G+  
DS2784G+T&R  
TEMP RANGE  
-40°C to +85°C  
-40°C to +85°C  
TOP MARK  
D2784  
PIN PACKAGE  
14 TDFN-EP*  
14 TDFN-EP*  
D2784  
+Denotes a lead(Pb)-free/RoHS-compliant package.  
T&R = Tape and reel.  
*EP = Exposed pad.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
ABSOLUTE MAXIMUM RATINGS  
Voltage Range on PLS Pin Relative to VSS  
Voltage Range on CP Pin Relative to VSS  
Voltage Range on DC Pin Relative to VSS  
Voltage Range on CC Pin Relative to VSS  
Voltage Range on All Other Pins Relative to VSS  
Maximum Voltage Range on VIN Pin Relative to VDD  
Continuous Sink Current, PIO, DQ  
-0.3V to +18V  
-0.3V to +12V  
-0.3V to (VCP + 0.3V)  
VDD - 0.3V to VCP + 0.3V  
-0.3V to +6.0V  
VDD + 0.3V  
20mA  
Continuous Sink Current, CC, DC  
10mA  
Operating Temperature Range  
Storage Temperature Range  
Lead Temperature (soldering,10s)  
-40°C to +85°C  
-55°C to +125°C  
+300°C  
Soldering Temperature (reflow)  
+260°C  
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections  
of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.  
ELECTRICAL CHARACTERISTICS  
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted. Typical values are at TA = +25°C.)  
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
+4.6  
4
UNITS  
Supply Voltage  
VDD  
IDD0  
(Note 1)  
Sleep mode  
+2.5  
V
1
Sleep mode, VDD = 2.5V  
0°C to +50°C  
IDD1  
IDD2  
IDD3  
0.4  
1.5  
µA  
Supply Current  
Active mode  
85  
125  
Active mode during SHA  
computation  
300  
500  
+3  
µA  
Temperature Accuracy  
Temperature Resolution  
Temperature Range  
-3  
0.125  
oC  
-128.000  
+127.875  
30  
4.0 ≤ VIN ≤ 4.6,  
VIN VDD + 0.3V  
2.5 ≤ VIN ≤ 4.6V,  
VIN VDD + 0.3V  
-30  
Voltage Accuracy, VIN  
mV  
-50  
+50  
4.6  
Voltage Resolution, VIN  
Voltage Range, VIN  
Input Resistance, VIN  
4.88  
1.56  
mV  
V
MΩ  
0
15  
Current Resolution  
Current Full Scale  
µV  
-51.2  
-1  
+51.2  
+1  
mV  
% full  
scale  
Current Gain Error  
Current Offset  
(Notes 2, 3, 4)  
(Notes 2, 3, 4)  
0ºC ≤ TA +50ºC  
-15  
-360  
-2  
+25  
0
µV  
Accumulated Current Offset  
µVh/day  
+2  
Time Base Error  
%
-3  
+3  
CP Output Voltage  
CP Startup Time  
VCP  
tSCP  
ICC + IDC = 0.9µA  
8.50  
9.25  
10.00  
V
CE = 0, DE = 0,  
CCP = 0.1µF, Active mode  
200  
ms  
VOHCC  
VOHDC  
Output High: CC, DC  
Output Low: CC  
IOH = -100µA (Note 5)  
IOL = 100µA  
VCP - 0.4  
V
V
VOLCC  
VDD + 0.1  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
PARAMETER  
Output Low: DC  
SYMBOL  
CONDITIONS  
IOL = 100µA  
MIN  
TYP  
MAX  
UNITS  
VOLDC  
0.1  
V
DQ, PIO Voltage Range  
DQ, PIO Input-Logic High  
DQ, PIO Input-Logic Low  
DQ, PIO Output-Logic Low  
-0.3  
1.5  
+5.5  
V
V
V
V
VIH  
VIL  
0.6  
0.4  
VOL  
IOL = 4mA  
Sleep mode,  
VPIN = VDD - 0.4V  
Active mode,  
VPIN = 0.4V  
DQ, PIO Pullup Current  
IPU  
IPD  
0.2  
µA  
µA  
DQ, PIO Pulldown Current  
0.2  
50  
DQ Input Capacitance  
DQ Sleep Timeout  
CDQ  
tSLEEP  
tWDB  
pF  
s
VDQ < VIL  
2
9
PIO, DQ Wake Debounce  
SHA-1 COMPUTATION TIMING  
Computation Time  
Sleep mode  
100  
ms  
tSHA  
30  
ms  
ELECTRICAL CHARACTERISTICS: Protection Circuit  
(VDD = 2.5V to 4.6V, TA = 0°C to +50°C, unless otherwise noted. Typical values are at TA = +25°C.)  
PARAMETER  
SYMBOL  
CONDITIONS  
OV = 11000b  
MIN  
4.457  
4.252  
-75  
TYP  
4.482  
4.277  
-100  
2.45  
-72  
MAX  
4.507  
4.302  
-125  
2.50  
-87  
UNITS  
V
Overvoltage Detect  
VOV  
V
VOV = 00011b  
Charge-Enable Voltage  
Undervoltage Detect  
VCE  
VUV  
Relative to VOV  
mV  
V
2.40  
-57  
OC = 11b  
OC = 00b  
OC = 11b  
OC = 00b  
SC = 1b  
Overcurrent Detect: Charge  
Overcurrent Detect: Discharge  
VCOC  
mV  
mV  
-15.5  
76  
-23.5  
96  
-31.5  
116  
VDOC  
23.5  
240  
35.5  
300  
47.5  
360  
mV  
mV  
Short-Circuit Current Detect  
Overvoltage Delay  
VSC  
tOVD  
SC = 0b  
120  
150  
180  
(Note 6)  
425  
1150  
ms  
Undervoltage Delay  
Overcurrent Delay  
Short-Circuit Delay  
Test Threshold  
tUVD  
tOCD  
tSCD  
VTP  
ITST  
IPPD  
(Notes 6, 7)  
84  
8
680  
12  
ms  
ms  
µs  
V
10  
120  
0.8  
20  
80  
0.3  
10  
30  
160  
1.5  
40  
COC, DOC conditions  
SC, COC, DOC condition  
Sleep mode  
Test Current  
µA  
µA  
PLS Pulldown Current  
200  
600  
VUV condition,  
max: VPLS = 15V,  
VDD = 1V  
Recovery Current  
IRC  
2.5  
5.0  
10.00  
mA  
min: VPLS = 4.2V,  
VDD = 2V  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
EEPROM RELIABILITY SPECIFICATION  
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted.)  
PARAMETER  
EEPROM Copy Time  
SYMBOL  
tEEC  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
ms  
10  
EEPROM Copy Endurance  
NEEC  
TA = +50°C  
50,000  
cycles  
ELECTRICAL CHARACTERISTICS: 1-Wire Interface, Standard  
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C, unless otherwise noted.)  
PARAMETER  
Time Slot  
SYMBOL  
tSLOT  
tREC  
CONDITIONS  
MIN  
60  
1
TYP  
MAX  
UNITS  
µs  
120  
Recovery Time  
µs  
Write-0 Low Time  
Write-1 Low Time  
Read-Data Valid  
Reset-Time High  
Reset-Time Low  
Presence-Detect High  
Presence-Detect Low  
tLOW0  
tLOW1  
tRDV  
60  
1
120  
15  
µs  
µs  
15  
µs  
tRSTH  
tRSTL  
tPDH  
480  
480  
15  
µs  
960  
60  
µs  
µs  
tPDL  
60  
240  
µs  
ELECTRICAL CHARACTERISTICS: 1-Wire Interface, Overdrive  
(VDD = 2.5V to 4.6V, TA = -20°C to +70°C.)  
PARAMETER  
Time Slot  
SYMBOL  
tSLOT  
tREC  
CONDITIONS  
MIN  
6
TYP  
MAX  
UNITS  
16  
µs  
µs  
µs  
µs  
µs  
µs  
µs  
µs  
µs  
Recovery Time  
1
Write-0 Low Time  
Write-1 Low Time  
Read-Data Valid  
Reset-Time High  
Reset-Time Low  
Presence-Detect High  
tLOW0  
tLOW1  
tRDV  
6
16  
2
1
2
tRSTH  
tRSTL  
tPDH  
48  
48  
2
80  
6
Presence-Detect Low  
tPDL  
8
24  
Note 1:  
All voltages are referenced to VSS.  
Note 2:  
Note 3:  
Note 4:  
Note 5:  
Note 6:  
Factory-calibrated accuracy. Higher accuracy can be achieved by in-system calibration by the user.  
Accumulation bias and offset bias registers set to 00h. NBEN bit set to 0.  
Parameters guaranteed by design.  
CP pin externally driven to 10V.  
Overvoltage and undervoltage delays (tOVD, tUVD) are reduced to 0s if the OV or UV condition is detected within 100ms of entering  
Active mode.  
Note 7:  
tUVD MIN determined by stepping the voltage on VIN from VUV + 250mV to VUV - 250mV.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
TYPICAL OPERATION CHARACTERISTICS  
CC FET Turn Off  
DC FET Turn Off  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
COC Delay  
DOC Delay  
6 of 43  
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
SC Delay  
OV Delay  
7 of 43  
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
UV Delay  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
TYPICAL OPERATING CIRCUIT  
PIN DESCRIPTION  
PIN  
1
2
NAME  
VDD  
CTG  
VSS  
FUNCTION  
Power-Supply Input. Chip supply input. Bypass with 0.1µF to VSS.  
Connect to Ground  
Device Ground. Chip ground and battery-side sense resistor input.  
Battery Voltage-Sense Input. Connect to positive cell terminal through decoupling  
network.  
3
4
5, 9, 10  
6
VIN  
N.C.  
PLS  
No Connection  
Pack Plus Terminal-Sense Input. Used to detect the removal of short-circuit, discharge  
overcurrent, and charge overcurrent conditions.  
Charge Control. Charge FET control output.  
Discharge Control. Discharge FET control output.  
Data Input/Output. Serial data I/O, includes weak pulldown to detect battery disconnect  
and can be configured as wake input.  
7
8
CC  
DC  
11  
12  
DQ  
Sense Resistor Connection. Pack minus terminal and pack-side sense resistor sense  
input.  
SNS  
13  
14  
CP  
PIO  
EP  
Charge Pump Output. Bypass with 0.1µF to VSS.  
Programmable I/O Pin. Can be configured as wake input.  
Exposed Pad. Connect to VSS or leave unconnected.  
DETAILED DESCRIPTION  
The DS2784 functions as an accurate fuel gauge, Li+ protector, and SHA-1-based authentication token. The fuel  
gauge provides accurate estimates of remaining capacity and reports timely voltage, temperature, and current-  
measurement data. Capacity estimates are calculated from a piecewise-linear model of the battery performance  
over load and temperature, and system parameters for full and empty conditions. The algorithm parameters are  
user programmable and can be modified in pack. Critical capacity and aging data are periodically saved to  
EEPROM in case of loss of power due to a short circuit or deep depletion.  
The Li+ protection function ensures safe, high-performance operation. nFET protection switches are driven with a  
9V charge pump that increase gate drive as the cell voltage decreases. The high-side topology preserves the  
ground path for serial communication while eliminating the parasitic charge path formed when the fuel gauge IC is  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
located inside the protection FETs in a low-side configuration. The thresholds for overvoltage, overcurrent, and  
short-circuit current are user programmable for easy customization to each cell and application.  
The 32-bit wide SHA-1 engine with 64-bit secret and 64-bit challenge words resists brute force and other attacks  
with financial-level HMAC security. The challenge of managing secrets in the supply chain is addressed with the  
compute next secret feature. The unique serial number or ROM ID can be used to assign a unique secret to each  
battery.  
BLOCK DIAGRAM  
VOLTAGE  
(VIN - VSSA)  
UV, CD  
10-Bit + sign  
ADC/MUX  
POWER MODE  
Control  
VIN  
TEMPERATURE  
LITHIUM ION  
PROTECTOR  
SNS  
VSS  
CURRENT  
(VSS - SNS)  
15-Bit + sign  
ADC  
PLS  
FuelPack™  
ALGORITHM  
PRECISION  
ANALOG  
VREF  
OSCILLATOR  
CC  
DC  
FET DRIVERS  
WKP, WKD  
Control and  
Status Registers  
CP  
PIO  
DQ  
PIO Logic  
CHARGE  
PUMP  
Pin Drivers  
and Pwr  
Switch  
VDD  
32 Byte  
Parameter  
EEPROM  
Control  
VDD_INT  
1-Wire Interface  
16 Byte User  
EEPROM  
DS2784  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
POWER MODES  
The DS2784 has two power modes: Active and Sleep. On initial power-up, the DS2784 defaults to Active mode. In  
Active mode, the DS2784 is fully functional with measurements and capacity estimation registers continuously  
updated. The protector circuit monitors the battery voltages and current for unsafe conditions. The protection FET  
gate drivers are enabled when conditions are deemed safe. Also, the SHA-1 authentication function is available in  
Active mode. When a SHA-1 computation is performed, the supply current increases to IDD3 for tSHA. In Sleep mode,  
the DS2784 conserves power by disabling measurement and capacity estimation functions, but preserves register  
contents. Gate drive to the protection FETs is disabled in Sleep. And the SHA-1 authentication feature is not  
operational.  
Sleep mode is entered under two different conditions: bus low and undervoltage. An enable bit makes entry into  
Sleep optional for each condition. Sleep mode is not entered if a charger is connected (VPLS > VDD + 50mV) or if a  
charge current of 1.6mV / RSNS is measured from SNS to VSS. The DS2784 exits Sleep mode upon charger  
connection and VIN ≥ VUV or a low to high transition on DQ.  
The bus-low condition, where the DQ pin is low for tSLEEP, indicates pack removal or system shutdown in which the  
1-Wire bus pullup voltage, VPULLUP, is not present. The Power mode (PMOD) bit must be set to enter Sleep when a  
bus-low condition occurs. After the DS2784 enters Sleep due to a bus-low condition, it is assumed that no charge  
or discharge current will flow and that coulomb counting is unnecessary.  
The second condition to enter Sleep is an undervoltage condition, which reduces battery drain due to the DS2784  
supply current and prevents over discharging the cell. The DS2784 transitions to Sleep if the VIN voltage is less  
than VUV (2.45V typical) and the undervoltage enable (UVEN) bit is set. The 1-Wire bus must be in a static state,  
that is, with DQ either high or low for tSLEEP. The DS2784 transitions from UVEN Sleep to Active mode when DQ  
changes logic state.  
The DS2784 has the “power switch” capability for waking the device and enabling the protection FETs when the  
host system is powered down. A simple dry-contact switch on the PIO pin or DQ pin can be used to wake up the  
battery pack. The power switch function is enabled using the PSPIO and PSDQ configuration bits in the control  
register. When PSPIO or PSDQ is set and a Sleep condition is satisfied, the PIO and DQ pins pull high weakly,  
then become armed to detect a low-going transition. A 100ms debounce period filters out glitches that can be  
caused when a sleeping battery is inserted into a system.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Figure 1. Sleep Mode State Diagram  
I/O Communication or  
Charger Connection  
Active  
PMOD = 0  
UVEN = 0  
SLEEP  
PSIO = 0  
PSDQ = 0  
Pull DQ Low  
Vin < VUV  
Active  
PMOD = 0  
UVEN = 1  
SLEEP  
PSIO = 0  
PSDQ = 1  
I/O Communication or  
Charger Connection  
Pull PIO Low  
Active  
PMOD = 1  
UVEN = 0  
SLEEP  
PSIO = 1  
PSDQ = 0  
DQ low for tSLEEP  
I/O Communication or  
Charger Connection  
Pull PIO low  
DQ low for tSLEEP  
Active  
PMOD = 1  
UVEN = 1  
SLEEP  
PSIO = 1  
PSDQ = 1  
Vin < VUV  
Pull DQ low  
I/O Communication or  
Charger Connection  
CONTROL REGISTER FORMAT  
All control register bits are read and write accessible. The control register is recalled from parameter EEPROM  
memory at power-up. Register bit values can be modified in shadow RAM after power-up. Power-up default values  
are saved using the Copy Data command.  
ADDRESS 60h  
BIT 7  
BIT 6  
BIT 5  
BIT 4  
BIT 3  
0
BIT 2  
BIT 1  
BIT 0  
X
NBEN  
UVEN  
PMOD RNAOP  
PSPIO  
PSDQ  
NBEN—Negative Blanking Enable. A value of 1 enables blanking of negative current values up to 25µV. A value of  
0 disables blanking of negative currents. The power-up default of NBEN = 0.  
UVEN—Undervoltage Enable. A value of 1 allows the DS2784 to enter Sleep mode when the voltage register value  
is less than VUV and DQ is stable at either logic level for tSLEEP. A value of 0 disables transitions to Sleep mode in an  
undervoltage condition.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
PMOD—Power Mode Enable. A value of 1 allows the DS2784 to enter Sleep mode when DQ is low for tSLEEP. A  
value of 0 disables DQ related transitions to Sleep mode.  
RNAOP—Read Net Address Op Code. A value of 0 selects 33h as the op code value for the Read Net Address  
command. A value of 1 selects 39h as the Read Net Address opcode value.  
0—Reserved bit, must be programmed to 0 for proper operation.  
PSPIO—Power-Switch PIO Enable. A value of 1 enables the PIO pin as a power-switch input. A value of 0 disables  
the power-switch input function on PIO pin. This control is independent of the PSDQ state.  
PSDQ—Power-Switch DQ Enable. A value of 1 enables the DQ pin as a power-switch input. A value of 0 disables  
the power-switch input function on DQ pin. This control is independent of the PSPIO state.  
X—Reserved Bit.  
Li+ PROTECTION CIRCUITRY  
During Active mode, the DS2784 constantly monitors SNS, VIN, and VPLS to protect the battery from overvoltage  
(overcharge), undervoltage (overdischarge), and excessive charge and discharge currents (overcurrent, short  
circuit). Table 1 summarizes the conditions that activate the protection circuit, the response of the DS2784, and the  
thresholds that release the DS2784 from a protection state.  
Table 1. Li+ Protection Conditions and DS2784 Responses  
ACTIVATION  
CONDITION  
RELEASE THRESHOLD  
THRESHOLD  
DELAY  
RESPONSE(2)  
VIN < VCE or (VSNS > 1.2mV  
Overvoltage  
Undervoltage  
VIN > VOV  
tOVD  
CC Off  
and VIN < VOV  
)
(3)  
CC Off, DC Off,  
Sleep Mode  
VPLS > VIN  
VIN < VUV  
VSNS < VCOC  
VSNS > VDOC  
VSNS > VSC  
tUVD  
tOCD  
tOCD  
tSCD  
(charger connected)  
(4)  
VPLS < VDD - VTP  
Overcurrent, Charge  
Overcurrent, Discharge  
Short Circuit  
CC Off, DC Off  
DC Off  
(charger removed)  
(5)  
VPLS > VDD - VTP  
(load removed)  
(5)  
VPLS > VDD - VTP  
DC Off  
(load removed)  
Note 1:  
Note 2:  
All voltages are with respect to VSS  
CC pin driven to VOLCC (VDD) for CC off response. DC pin driven to VOLDC (VSS) for DC off response.  
.
Note 3:  
If VIN < VUV when charger connection is detected, release is delayed until VIN ≥ VUV. The recovery charge path provides an internal  
current limit (IRC) to safely charge the battery. If the device does not enter sleep mode for an UV condition (UVEN=0) then the  
FETs will turn on once VIN > VUV  
.
With test current I flowing from PLS to VSS (pulldown on PLS) enabled.  
Note 4:  
Note 5:  
TST  
With test current I flowing from VDD to PLS (pullup on PLS).  
TST  
Overvoltage. If the voltage on VIN exceeds the overvoltage threshold (VOV) for a period longer than overvoltage  
delay (tOVD), the CC pin is driven low to shut off the external-charge FET, and the OV flag in the protection register  
is set. The DC output remains high during overvoltage to allow discharging. When VIN falls below the charge enable  
threshold, VCE, the DS2784 turns the charge FET on by driving CC high. The DS2784 drives CC high before  
VIN < VCE if a discharge condition persists with VSNS ≥ 1.2mV and VIN < VOV.  
Undervoltage. If VIN drops below the undervoltage threshold (VUV) for a period longer than undervoltage delay  
(tUVD), the DS2784 shuts off the charge and discharge FETs and sets the UV flag in the protection register. If UVEN  
is set, the DS2784 also enters Sleep mode. The DS2784 provides a current-limited recovery charge path (IRC) from  
PLS to VDD to gently charge severely depleted cells. The recovery charge path is enabled when  
0 VIN < (VOV - 100mV). Once VIN reaches 2.45V (typ), the DS2784 returns to normal operation. The DS2784  
transitions from Sleep to Active mode and the CC and DC outputs are driven high to turn on the charge and  
13 of 43  
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
discharge FETs. . If the device does not enter sleep mode for an UV condition (UVEN=0) then the FETs will turn  
on once VIN > VUV.  
Overcurrent, Charge Direction (COC). Charge current develops a negative voltage on VSNS with respect to VSS. If  
VSNS is less than the charge overcurrent threshold (VCOC) for a period longer than overcurrent delay (tOCD), the  
DS2784 shuts off both external FETs and sets the COC flag in the protection register. The charge current path is  
not re-established until the voltage on the PLS pin drops below VDD - VTP. The DS2784 provides a pulldown current  
(ITST) from PLS to VSS to pull PLS down in order to detect the removal of the offending charge current source.  
Overcurrent, Discharge Direction (DOC). Discharge current develops a positive voltage on VSNS with respect to  
VSS. If VSNS exceeds the discharge overcurrent threshold (VDOC) for a period longer than tOCD, the DS2784 shuts off  
the external discharge FET and sets the DOC flag in the protection register. The discharge current path is not re-  
established until the voltage on PLS rises above VDD - VTP. The DS2784 provides a test current (ITST) from VDD to  
PLS to pull PLS up in order to detect the removal of the offending low-impedance load.  
Short Circuit. If VSNS exceeds short-circuit threshold VSC for a period longer than short-circuit delay (tSCD), the  
DS2784 shuts off the external discharge FET and sets the DOC flag in the protection register. The discharge  
current path is not re-established until the voltage on PLS rises above VDD - VTP. The DS2784 provides a test  
current of value (ITST) from VDD to PLS to pull PLS up in order to detect the removal of the short circuit.  
Figure 2. Li+ Protection Circuitry Example Waveforms  
VOV  
VCE  
VIN  
VUV  
VSC  
Discharge  
VDOC  
0
VSNS  
-VCOC  
Charge  
VCP  
VDD  
CC  
DC  
tOVD  
tOVD  
tOCD  
tUVD  
VCP  
tSCD  
tOCD  
tUVD  
VPLS  
ACTIVE  
SLEEP  
Power  
Mode  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Summary. All the protection conditions previously described are logic ANDed to affect the CC and DC outputs.  
CC = (Overvoltage) AND (Undervoltage) AND (Overcurrent, Charge Direction)  
AND (Protection Register Bit CE)  
DC = (Undervoltage) AND (Overcurrent, Either Direction) AND (Short Circuit)  
AND (Protection Register Bit DE)  
PROTECTION REGISTER FORMAT  
The protection register reports events detected by the Li+ safety circuit on bits 2 to 7. Bits 0 and 1 are used to  
disable the charge and discharge FET gate drivers. Bits 2 to 7 are set by internal hardware only. Bits 2 and 3 are  
cleared by hardware only. Bits 4 to 7 are cleared by writing the register with a 0 in the bit position of interest. Writing  
a 1 to bits 4 to 7 has no effect on the register. Bits 0 and 1 are set on power-up and a transition from Sleep to  
Active modes. While in Active mode, these bits can be cleared to disable the FET gate drive of either or both FETs.  
Setting these bits only turns on the FETs if there are no protection faults.  
ADDRESS 00h  
BIT 7  
OV  
BIT 6  
UV  
BIT 5  
COC  
BIT 4  
DOC  
BIT 3  
CC  
BIT 2  
DC  
BIT 1  
CE  
BIT 0  
DE  
OV—Overvoltage Flag. OV is set to indicate that an overvoltage condition has been detected. The voltage on VIN  
has persisted above the VOV threshold for tOV. OV remains set until written to a 0 or cleared by a power-on reset or  
transition to Sleep mode.  
UV—Undervoltage Flag. UV is a read-only mirror of the UVF flag located in the status register. UVF is set to  
indicate that VIN < VUV . The UVF bit must be written to 0 to clear UV and UVF.  
COC—Charge Overcurrent Flag. COC is set to indicate that an overcurrent condition has occurred during a charge.  
The sense-resistor voltage has persisted above the VCOC threshold for tOC. COC remains set until written to a 0,  
cleared by a power-on reset, or transition to Sleep mode.  
DOC—Discharge Overcurrent Flag. DOC is set to indicate that an overcurrent condition has occurred during a  
discharge. The sense-resistor voltage has persisted above the VDOC threshold for tOC. DOC remains set until written  
to a 0, cleared by a power-on reset, or transition to Sleep mode.  
CC—Charge Control Flag. CC indicates the logic state of the CC pin driver. CC flag is set to indicate CC high. CC  
flag is cleared to indicate CC low. CC flag is read only.  
DC—Discharge Control Flag. DC indicates the logic state of the DC pin driver. DC flag is set to indicate DC high.  
DC flag is cleared to indicate DC low. DC flag is read only.  
CE—Charge Enable Bit. CE must be set to allow the CC pin to drive the charge FET to the on state. CE acts as an  
enable input to the safety circuit. If all safety conditions are met AND CE is set, the CC pin drives to VCP. If CE is  
cleared, the CC pin is driven low to disable the charge FET.  
DE—Discharge Enable Bit. DE must be set to allow the DC pin to drive the discharge FET to the on state. DE acts  
as an enable input to the safety circuit. If all safety conditions are met AND DE is set, the DC pin drives to VCP. If  
DE is cleared, the DC pin is driven low to disable the charge FET.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
PROTECTOR THRESHOLD REGISTER FORMAT  
The 8-bit threshold register consists of bit fields for setting the overvoltage threshold, charge overcurrent threshold,  
discharge overcurrent threshold, and short-circuit threshold for the protection circuit.  
ADDRESS 7Fh  
BIT 7  
BIT 6  
BIT 5  
BIT 4  
BIT 3  
BIT 2  
SC0  
BIT 1  
OC1  
BIT 0  
OC0  
VOV4  
VOV3  
VOV2  
VOV1  
VOV0  
Table 2. VOV Threshold  
VOV BIT FIELD  
0 0 0 0 0  
0 0 0 0 1  
0 0 0 1 0  
0 0 0 1 1  
0 0 1 0 0  
0 0 1 0 1  
0 0 1 1 0  
0 0 1 1 1  
0 1 0 0 0  
0 1 0 0 1  
0 1 0 1 0  
0 1 0 1 1  
0 1 1 0 0  
0 1 1 0 1  
0 1 1 1 0  
0 1 1 1 1  
VOV  
VOV BIT FIELD  
1 0 0 0 0  
1 0 0 0 1  
1 0 0 1 0  
1 0 0 1 1  
1 0 1 0 0  
1 0 1 0 1  
1 0 1 1 0  
1 0 1 1 1  
1 1 0 0 0  
1 1 0 0 1  
1 1 0 1 0  
1 1 0 1 1  
1 1 1 0 0  
1 1 1 0 1  
1 1 1 1 0  
1 1 1 1 1  
VOV  
4.248  
4.258  
4.268  
4.277  
4.287  
4.297  
4.307  
4.316  
4.326  
4.336  
4.346  
4.356  
4.365  
4.375  
4.385  
4.395  
4.404  
4.414  
4.424  
4.434  
4.443  
4.453  
4.463  
4.473  
4.482  
4.492  
4.502  
4.512  
4.522  
4.531  
4.541  
4.551  
Table 3. COC, DOC Threshold  
OC[1:0] BIT FIELD  
VCOC (mV)  
-23.5  
VDOC (mV)  
0 0  
0 1  
1 0  
35.5  
-36  
48  
-48  
72  
1 1  
-72  
96  
Table 4. SC Threshold  
SC0 BIT FIELD  
VSC (mV)  
0
150  
1
300  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
VOLTAGE MEASUREMENT  
Battery voltage is measured every 440ms on the VIN pin with respect to VSS. Measurements have a 0 to 4.6V range  
and a 4.88mV resolution. The value is stored in the voltage register in two’s complement form and is updated every  
440ms. Voltages above the maximum register value are reported at the maximum value; voltages below the  
minimum register value are reported at the minimum value.  
VOLTAGE REGISTER FORMAT  
MSB—ADDRESS 0Ch  
28 27 26 25  
LSB—ADDRESS 0Dh  
20  
S
29  
24  
23  
22  
21  
X
X
X
X
X
MSb  
LSb  
MSb  
LSb  
Units: 4.886mV  
“S”: Sign Bit(s), “X”: Reserved  
TEMPERATURE MEASUREMENT  
The DS2784 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125°C.  
Temperature measurements are updated every 440ms and placed in the temperature register in two’s complement  
form.  
TEMPERATURE REGISTER FORMAT  
MSB—ADDRESS 0Ah  
28 27 26 25  
LSB—ADDRESS 0Bh  
20  
S
29  
24  
23  
22  
21  
X
X
X
X
X
MSb  
LSb  
MSb  
LSb  
Units: 0.125°C  
“S”: Sign Bit(s), “X”: Reserved  
Note: Temperature and battery voltage (VIN) are measured using the same ADC. Therefore, measurements are a 220ms average updated  
every 440ms.  
CURRENT MEASUREMENT  
The DS2784 continually measures the current flow into and out of the battery by measuring the voltage drop across  
a low-value current-sense resistor, RSNS. The voltage-sense range between SNS and VSS is ±51.2mV. The input  
linearly converts peak-signal amplitudes up to 102.4mV as long as the continuous signal level (average over the  
conversion cycle period) does not exceed ±51.2mV. The ADC samples the input differentially at 18.6kHz and  
updates the current register at the completion of each conversion cycle (3.52s). Charge currents above the  
maximum register value are reported as 7FFFh. Discharge currents below the minimum register value are reported  
as 8000h.  
CURRENT REGISTER FORMAT  
MSB—ADDRESS 0Eh  
LSB—ADDRESS 0Fh  
25 24 23 22  
S
214 213 212 211 210 29  
28  
27  
26  
21 20  
LSb  
MSb  
LSb  
MSb  
“S”: Sign Bit(s)  
Units: 1.5625µV/RSNS  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
The average current register reports an average current level over the preceding 28s. The register value is updated  
every 28s in two’s complement form, and represents an average of the eight preceding current register values.  
AVERAGE CURRENT REGISTER FORMAT  
MSB—ADDRESS 08h  
LSB—ADDRESS 09h  
25 24 23 22  
S
214 213 212 211 210 29  
28  
27  
26  
21 20  
LSb  
MSb  
LSb  
MSb  
“S”: Sign Bit(s)  
Units: 1.5625µV/RSNS  
CURRENT OFFSET CORRECTION  
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs  
approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements.  
During the offset correction conversion, the ADC does not measure the sense-resistor signal. A maximum error of  
1/1024 in the accumulated current register (ACR) is possible; however, to reduce the error, the current  
measurement made just prior to the offset conversion is retained in the current register and is substituted for the  
dropped current measurement in the current accumulation process. Therefore, the accumulated current error due  
to offset correction is typically much less than 1/1024.  
CURRENT OFFSET BIAS  
The current offset bias (COB) value allows a programmable offset value to be added to raw current measurements.  
The result of the raw current measurement plus COB is displayed as the current measurement result in the current  
register, and is used for current accumulation. COB can be used to correct for a static offset error, or can be used  
to intentionally skew the current results and, therefore, the current accumulation.  
Read and write access is allowed to COB. Whenever the COB is written, the new value is applied to all subsequent  
current measurements. COB can be programmed in 1.56µV steps to any value between +198.1µV and -199.7µV.  
The COB value is stored as a two’s complement value in EEPROM. The COB is loaded on power-up from  
EEPROM memory. The factory default value is 00h.  
The difference between the CAB and COB is that the CAB is not subject to current blanking. Offset currents  
between 100µV and -25µV are not accumulated if the offset is made by the COB. Offset currents between 100µV  
and -25µV are accumulated if they are made by the CAB.  
CURRENT OFFSET BIAS REGISTER FORMAT  
ADDRESS 7Bh  
S
26  
25  
24  
23  
22  
21 20  
LSb  
MSb  
“S”: Sign Bit(s)  
Units: 1.56µV/RSNS  
CURRENT BLANKING  
The current blanking feature modifies current measurement result prior to being accumulated in the ACR. Current  
blanking occurs conditionally when a current measurement (raw current + COBR) falls in one of two defined  
ranges. The first range prevents charge currents less than 100µV from being accumulated. The second range  
prevents discharge currents less than 25µV in magnitude from being accumulated. Charge current blanking is  
always performed; however, discharge current blanking must be enabled by setting the NBEN bit in the control  
register. See the register description for additional information.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
CURRENT MEASUREMENT CALIBRATION  
The DS2784’s current measurement gain can be adjusted through the RSGAIN register, which is factory calibrated  
to meet the data sheet-specified accuracy. RSGAIN is user accessible and can be reprogrammed after module or  
pack manufacture to improve the current measurement accuracy. Adjusting RSGAIN can correct for variation in an  
external sense resistor’s nominal value, and allows the use of low-cost, nonprecision, current-sense resistors.  
RSGAIN is an 11-bit value stored in 2 bytes of the parameter EEPROM memory block. The RSGAIN value adjusts  
the gain from 0 to 1.999 in steps of 0.001 (precisely 2-10). The user must program RSGAIN cautiously to ensure  
accurate current measurement. When shipped from the factory, the gain calibration value is stored in two separate  
locations in the parameter EEPROM block: RSGAIN, which is reprogrammable, and FRSGAIN, which is read only.  
RSGAIN determines the gain used in the current measurement. The FRSGAIN value is provided to preserve the  
factory calibration value only and is not used to calibrate the current measurement. The 16-bit FRSGAIN value is  
readable from addresses B0h and B1h.  
CURRENT MEASUREMENT GAIN REGISTER FORMAT  
MSB—ADDRESS 78h  
210 29  
LSB—ADDRESS 79h  
25 24 23 22  
X
X
X
X
X
28  
27  
26  
21 20  
LSb  
MSb  
LSb  
MSb  
Units: 2-10  
SENSE RESISTOR TEMPERATURE COMPENSATION  
The DS2784 can temperature compensate the current-sense resistor to correct for variation in a sense resistor’s  
value overtemperature. The DS2784 is factory programmed with the sense-resistor temperature coefficient, RSTC,  
set to zero, which turns off the temperature compensation function. RSTC is user accessible and can be  
reprogrammed after module or pack manufacture to improve the current accuracy when using a high-temperature  
coefficient current-sense resistor. RSTC is an 8-bit value stored in the parameter EEPROM memory block. The  
RSTC value sets the temperature coefficient from 0 to +7782ppm/ºC in steps of 30.5ppm/ºC. The user must  
program RSTC cautiously to ensure accurate current measurement.  
Temperature compensation adjustments are made when the temperature register crosses 0.5oC boundaries. The  
temperature compensation is most effective with the resistor placed as close as possible to the VSS terminal. This  
optimizes thermal coupling of the resistor to the on-chip temperature sensor.  
SENSE RESISTOR TEMPERATURE COMPENSATION REGISTER FORMAT  
ADDRESS 7Ah  
27  
26  
25  
24  
23  
22  
21 20  
LSb  
MSb  
Units: 30.5ppm/ºC  
CURRENT ACCUMULATION  
Current measurements are internally summed, or accumulated, at the completion of each conversion period and  
the results are stored in the ACR. The accuracy of the ACR is dependent on both the current measurement and the  
conversion time base. The ACR has a range of 0 to 409.6mVh with an LSb of 6.25µVh. Additional registers hold  
fractional results of each accumulation to avoid truncation errors. The fractional result bits are not user accessible.  
Accumulation of charge current above the maximum register value is reported at the maximum value; conversely,  
accumulation of discharge current below the minimum register value is reported at the minimum value.  
Charge currents (positive current register values) less than 100µV are not accumulated in order to mask the effect  
of accumulating small positive offset errors over long periods. This limits the minimum charge current, for coulomb-  
counting purposes, to 5mA for RSNS = 0.020and 20mA for RSNS = 0.005.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Read and write access is allowed to the ACR. The ACR must be written MSB first then LSB. Whenever the ACR is  
written, the fractional accumulation result bits are cleared. The write must be completed in 3.5s (one ACR update  
period). A write to the ACR forces the ADC to perform an offset correction conversion and update the internal offset  
correction factor. The current measurement and accumulation begin with the second conversion following a write to  
the ACR.  
The ACR value is backed up to EEPROM in case of power loss. The ACR value is recovered from EEPROM on  
power-up. See Table 8 for specific address location and backup frequency.  
ACCUMULATED CURRENT REGISTER FORMAT  
MSB—ADDRESS 10h  
LSB—ADDRESS 11h  
215 214 213 212 211 210 29  
MSb  
28  
27  
26  
25  
24  
23  
22  
21 20  
LSb  
LSb  
MSb  
Units: 6.25µVh/RSNS  
Table 5. Resolution and Range vs. Sense Resistor  
RSNS  
VSS - VSNS  
20mΩ  
15mΩ  
10mΩ  
5mΩ  
Current Resolution  
1.5625µV  
78.13µA  
104.2µA  
156.3µA  
312.5µA  
Current Range  
ACR Resolution  
ACR Range  
±51.2mV  
6.25µVh  
±2.56A  
±3.41A  
±5.12A  
625µAh  
40.96Ah  
±10.24A  
1.250mAh  
81.92Ah  
312.5µAh 416.7µAh  
20.48Ah 27.31Ah  
409.6mVh  
ACCUMULATION BIAS  
In some designs a systematic error or an application preference requires the application of an arbitrary bias to the  
current accumulation process. The current accumulation bias register (CAB) allows a user-programmed constant  
positive or negative polarity bias to be included in the current accumulation process. The value in CAB can be used  
to estimate battery currents that do not flow through the sense resistor, estimate battery self-discharge or estimate  
current levels below the current measurement resolution. The user programmed two’s complement value, with bit  
weighting the same as the current register, is added to the ACR once per current conversion cycle. The CAB is  
loaded on power-up from EEPROM memory.  
The difference between the CAB and COB is that the CAB is not subject to current blanking. Offset currents  
between 100µV and -25µV are not accumulated if the offset is made by the COB. Offset currents between 100µV  
and -25µV are accumulated if they are made by the CAB.  
CURRENT ACCUMULATION BIAS REGISTER FORMAT  
ADDRESS 61h  
S
26  
25  
24  
23  
22  
21 20  
LSb  
MSb  
“S”: Sign Bit  
Units: 1.5625µV/RSNS  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
CAPACITY ESTIMATION ALGORITHM  
Remaining capacity estimation uses real-time measured values, stored parameters describing the cell  
characteristics, and application operating limits. Figure 3 describes the algorithm inputs and outputs.  
Figure 3. Top-Level Algorithm Diagram  
Voltage  
(R)  
(R)  
(R)  
FULL(T)  
(R)  
(R)  
(R)  
Temperature  
Current  
Capacity Look-up  
Available Capacity Calculation  
ACR Housekeeping  
Age Estimator  
Active Empty (T)  
Standby Empty (T)  
Accumulated  
Current (ACR) (R/W)  
Remaining Active Absolute  
Capacity (RAAC) mAh  
(R)  
(R)  
(R)  
(R)  
Average Current (R)  
Remaining Standby Absolute  
Capacity (RSAC) mAh  
Learn Function  
Cell  
Model  
Parameters  
Remaining Active Relative  
Capacity (RARC) %  
(EEPROM)  
Remaining Standby Relative  
Capacity (RSRC) %  
Aging Cap (AC)  
(2 bytes EE)  
User Memory (EEPROM)  
16 bytes  
Age Scalar (AS)  
(1 bytes EE)  
Sense Resistor’  
(RSNSP) (1byte EE)  
Charge Voltage  
(VCHG) (1 byte EE)  
Min Chg Current  
(IMIN) (1 byte EE)  
Empty Voltage  
(VAE) (1 byte EE)  
Empty Current (IAE)  
(1 byte EE)  
MODELING CELL CHARACTERISTICS  
To achieve reasonable accuracy in estimating remaining capacity, the cell performance characteristics  
overtemperature, load current, and charge-termination point must be considered. Since the behavior of Li+ cells is  
nonlinear, these characteristics must be included in the capacity estimation to achieve an acceptable level of  
accuracy in the capacity estimation. The FuelPack™ method used in the DS2784 is described in general in  
Application Note 131: Lithium-Ion Cell Fuel Gauging with Maxim Battery Monitor ICs. To facilitate efficient  
implementation in hardware, a modified version of the method outlined in AN131 is used to store cell characteristics  
in the DS2784. Full and empty points are retrieved in a lookup process which retraces a piece-wise linear model  
consisting of three model curves named full, active empty, and standby empty. Each model curve is constructed  
with 5-line segments, numbered 1 through 5. Above 40°C, the segment 5 model curves extend infinitely with zero  
slope, approximating the nearly flat change in capacity of Li+ cells at temperatures above 40°C. Segment 4 of each  
model curves originates at +40°C on its upper end and extends downward in temperature to the junction with  
segment 3. Segment 3 joins with segment 2, which in turn joins with segment 1. Segment 1 of each model curve  
extends from the junction with segment 2 to infinitely colder temperatures. The three junctions or breakpoints that  
join the segments (labeled TBP12, TBP23, and TBP34 in Figure 4) are programmable in 1°C increments from -  
128°C to +40°C. The slope or derivative for segments 1, 2, 3, and 4 are also programmable over a range of 0 to  
15,555ppm, in steps of 61ppm.  
FuelPack is a trademark of Maxim Integrated Products, Inc.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Figure 4. Cell Model Example Diagram  
SEGMENT 1  
SEG. 2  
SEG. 3  
SEG. 4  
SEG. 5  
100%  
FULL  
DERIVATIVE  
[PPM/°C]  
CELL  
CHARACTERIZATION  
DATA POINTS  
ACTIVE  
EMPTY  
STANDBY  
EMPTY  
TBP12  
TBP23  
TBP34  
40°C  
Full—The full curve defines how the full point of a given cell varies over temperature for a given charge termination.  
The application’s charge termination method should be used to determine the table values. The DS2784  
reconstructs the full line from the cell characteristic table to determine the full capacity of the battery at each  
temperature. Reconstruction occurs in one-degree temperature increments.  
Active Empty—The active-empty curve defines the variation of the active-empty point over temperature. The  
active-empty point is defined as the minimum voltage required for system operation at a discharge rate based on a  
high-level load current (one that is sustained during a high-power operating mode). This load current is  
programmed as the active-empty current (IAE), and should be a 3.5s average value to correspond to values read  
from the current register. The specified minimum voltage, or active empty voltage (VAE), should be a 220ms  
average value to correspond to the values read from the voltage register. The DS2784 reconstructs the active  
empty line from the cell characteristic table to determine the active empty capacity of the battery at each  
temperature. Reconstruction occurs in one-degree temperature increments.  
Standby Empty—The standby-empty curve defines the variation of the standby-empty point over temperature. The  
standby-empty point is defined as the minimum voltage required for standby operation at a discharge rate dictated  
by the application standby current. In typical handheld applications, standby empty represents the point that the  
battery can no longer support DRAM refresh and thus the standby voltage is set by the minimum DRAM voltage-  
supply requirements. In other applications, standby empty can represent the point that the battery can no longer  
support a subset of the full application operation, such as games or organizer functions. The standby load current  
and voltage are used for determining the cell characteristics but are not programmed into the DS2784. The DS2784  
reconstructs the standby-empty line from the cell characteristic table to determine the standby-empty capacity of  
the battery at each temperature. Reconstruction occurs in one-degree temperature increments.  
CELL MODEL CONSTRUCTION  
The model is constructed with all points normalized to the fully charged state at +40°C. All values are stored in the  
cell parameter EEPROM block. The +40°C full value is stored in µVhr with an LSB of 6.25µVhr. The +40°C active  
empty value is stored as a percentage of +40°C full with a resolution of 2-10. Standby empty at +40°C is, by  
definition, zero and, therefore, no storage is required. The slopes (derivatives) of the 4 segments for each model  
curve are stored in the cell parameter EEPROM block as ppm/°C. The breakpoint temperatures of each segment  
are stored there also (see Application Note 3584: Storing Battery Fuel Gauge Parameters in DS2780 for more  
details on how values are stored). An example of data stored in this manner is shown in Table 6.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Table 6. Example Cell Characterization Table (Normalized to +40°C)  
Manufacturer’s Rated Cell Capacity: 1000mAh  
Charge Voltage: 4.2V  
Active Empty (V): 3.0V  
Termination Current: 50mA  
Active Empty (I): 300mA  
Sense Resistor: 0.020  
TBP12  
TBP23  
TBP34  
Segment  
Breakpoints  
-12°C  
0°C  
18°C  
+40°C  
Nominal  
(mAh)  
1051  
Seg. 1  
ppm/°C  
Seg. 2  
ppm/°C  
Seg. 3  
ppm/°C  
Seg. 4  
ppm/°C  
Full  
3601  
2380  
1404  
3113  
1099  
427  
1163  
671  
244  
854  
305  
183  
Active Empty  
Standby Empty  
Figure 5. Lookup Function Diagram  
FULL(T) *  
AE(T) *  
CELL MODEL  
PARAMETERS  
LOOKUP  
FUNCTION  
(EEPROM)  
SE(T) *  
TEMPERATURE  
*See Result Registers section for a description of these registers.  
APPLICATION PARAMETERS  
In addition to cell model characteristics, several application parameters are needed to detect the full and empty  
points, as well as calculate results in mAh units.  
Sense Resistor Prime (RSNSP[1/])—RSNSP stores the value of the sense resistor for use in computing the absolute  
capacity results. The resistance is stored as a 1-byte conductance value with units of mhos (1/Ω). RSNSP supports  
resistor values of 1to 3.922m. RSNS is located in the parameter EEPROM block.  
RSNSP = 1/RSNS (units of mhos; 1/)  
Charge Voltage (VCHG)—VCHG stores the charge voltage threshold used to detect a fully charged state. The  
voltage is stored as a 1-byte value with units of 19.5mV and can range from 0V to 4.978V. VCHG should be set  
marginally less than the cell voltage at the end of the charge cycle to ensure reliable charge termination detection.  
VCHG is located in the parameter EEPROM block.  
Minimum Charge Current (IMIN)—IMIN stores the charge current threshold used to detect a fully charged state. It  
is stored as a 1-byte value with units of 50µV (IMIN x RSNS) and can range from 0 to 12.75mV. Assuming RSNS  
=
20m, IMIN can be programmed from 0mA to 637.5mA in 2.5mA steps. IMIN should be set marginally greater than  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
the charge current at the end of the charge cycle to ensure reliable charge termination detection. IMIN is located in  
the parameter EEPROM block.  
Active Empty Voltage (VAE)—VAE stores the voltage threshold used to detect the active empty point. The value  
is stored in 1-byte with units of 19.5mV and can range from 0V to 4.978V. VAE is located in the parameter  
EEPROM block. See the Modeling Cell Characteristics section for more information.  
Active Empty Current (IAE)—IAE stores the discharge current threshold used to detect the active empty point.  
The unsigned value represents the magnitude of the discharge current and is stored in 1-byte with units of 200µV  
and can range from 0 to 51.2mV. Assuming RSNS = 20m, IAE can be programmed from 0mA to 2550mA in 10mA  
steps. IAE is located in the Parameter EEPROM block. See the Cell Model Construction section for more  
information.  
Aging Capacity (AC)—AC stores the rated cell capacity, which is used to estimate the decrease in battery  
capacity that occurs during normal use. The value is stored in 2 bytes in the same units as the ACR (6.25µVh).  
When set to the manufacturer’s rated cell capacity the aging estimation rate is approximately 2.4% per 100 cycles  
of equivalent full capacity discharges. Partial discharge cycles are added to form equivalent full capacity  
discharges. The default aging estimation results in 88% capacity after 500 equivalent cycles. The aging estimation  
rate can be adjusted by setting the AC to a value other than the cell manufacturer’s rating. Setting AC to a lower  
value, accelerates the aging estimation rate. Setting AC to a higher value, retards the aging estimation rate. The  
AC is located in the parameter EEPROM block.  
Age Scalar (AS)—AS adjusts the cell capacity estimation results downward to compensate for aging. The AS is a  
1-byte value that has a range of 49.2% to 100%. The LSb is weighted at 0.78% (precisely 2-7). A value of 100%  
(128 decimal or 80h) represents an unaged battery. A value of 95% is recommended as the starting AS value at the  
time of pack manufacture to allow the learning of a larger capacity on batteries that have an initial capacity greater  
than the rated cell capacity programmed in the cell characteristic table. The AS is modified by aging estimation  
introduced under aging capacity and by the capacity-learn function. The host system has read and write access to  
the AS, however caution should exercised when writing it to ensure that the cumulative aging estimate is not  
overwritten with an incorrect value. The AS is automatically saved to EEPROM (see Table 7 for details). The  
EEPROM value is recalled on power-up.  
Full capacity estimation based on the learn function is more accurate than the cycle-count-based estimation. The  
learn function reflects the current performance of the cell. Cycle count based estimation is an approximation  
derived from the manufacturer’s recommendation for a typical cell. Batteries are typically considered worn-out when  
the full capacity reaches 80% of the rated capacity, therefore, the AS value is not required to range to 0%. It is  
clamped to 50% (64d or 40h). If a value of 50% is read from the AS, the host should prompt the user to initiate a  
learning cycle.  
CAPACITY ESTIMATION OPERATION  
Aging Estimation  
As discussed above, the AS register value is adjusted occasionally based on cumulative discharge. As the ACR  
register decrements during each discharge cycle, an internal counter is incremented until equal to 32 times the AC.  
The AS is then decremented by one, resulting in a decrease of the scaled full battery capacity by 0.78%  
(approximately 2.4% per 100 cycles). See the AC register description above for recommendations on customizing  
the age-estimation rate.  
Learn Function  
Since Li+ cells exhibit charge efficiencies near unity, the charge delivered to a Li+ cell from a known empty point to  
a known full point is a dependable measure of the cell capacity. A continuous charge from empty to full results in a  
learn cycle. First, the active empty point must be detected. The learn flag (LEARNF) is set at this point. Then, once  
charging starts, the charge must continue uninterrupted until the battery is charged to full. Upon detecting full,  
LEARNF is cleared, the charge to full (CHGTF) flag is set, and the age scalar (AS) is adjusted according to the  
learned capacity of the cell.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
ACR Housekeeping  
The ACR value is adjusted occasionally to maintain the coulomb count within the model curve boundaries. When  
the battery is charged to full (CHGTF set), the ACR is set equal to the age scaled full lookup value at the present  
temperature. If a learn cycle is in progress, correction of the ACR value occurs after the age scalar (AS) is updated.  
When an empty condition is detected (LEARNF and/or AEF set), the ACR adjustment is conditional:  
.
If the AEF is set and the LEARNF is not set, then the active-empty point was not detected. The battery is likely  
below the active-empty capacity of the model. The ACR is set to the active-empty model value at present temp  
only if it is greater than the active-empty model value at present temp.  
.
.
If the AEF is set, the LEARNF is not set, and the ACR is below the active-empty model value at present temp  
the ACR is NOT updated.  
If the LEARNF is set, then the battery is at the active-empty point and the ACR is set to the active-empty model  
value.  
Full Detect  
Full detection occurs when the voltage (V) readings remain continuously above the charge voltage (VCHG)  
threshold for the duration of two average current (IAVG) readings, and both IAVG readings are below terminating  
current (IMIN). The two consecutive IAVG readings must also be positive and nonzero (> 16 LSB). This ensures  
that removing the battery from the charger does not result in a false detection of full. Full detect sets the charge to  
full (CHGTF) bit in the status register.  
Active-Empty Point Detect  
Active-empty point detection occurs when the voltage register drops below the VAE threshold AND the two  
previous current readings are above IAE. This captures the event of the battery reaching the active-empty point.  
Note that the two previous current readings must be negative and greater in magnitude than IAE, that is, a larger  
discharge current than specified by the IAE threshold. Qualifying the voltage level with the discharge rate ensures  
that the active-empty point is not detected at loads much lighter than those used to construct the model. Also, the  
active-empty point must not be detected when a deep discharge at a very light load is followed by a load greater  
than IAE. Either case would cause a learn cycle on the following charge to include part of the standby capacity in  
the measurement of the active capacity. Active-empty point detection sets the learn flag (LEARNF) bit in the status  
register. Do not confuse the active-empty point with the active-empty flag. The active-empty flag is set only when  
the VAE threshold is passed.  
STATUS REGISTER FORMAT  
The status register contains bits that report the device status. All bits are set internally. The CHGTF, AEF, SEF, and  
LEARNF bits are read only. The UVF and PORF bits can be cleared by writing a zero to the bit locations.  
ADDRESS 01h  
BIT 7  
BIT 6  
AEF  
BIT 5  
SEF  
BIT 4  
BIT 3  
X
BIT 2  
UVF  
BIT 1  
BIT 0  
X
CHGTF  
LEARNF  
PORF  
CHGTF—Charge-Termination Flag. CHGTF is set to indicate that the voltage and average current register values  
have persisted above the VCHG and below the IMIN thresholds sufficiently long to detect a fully charged condition.  
CHGTF is cleared when RARC is less than 90%. CHGTF is read only.  
AEF—Active-Empty Flag. AEF is set to indicate that the battery is at or below the active-empty point. AEF is set  
when the voltage register value is less than the VAE threshold. AEF is cleared when RARC is greater than 5%.  
AEF is read only.  
SEF—Standby-Empty Flag. SEF is set to indicate RSRC is less than 10%. SEF is cleared when RSRC is greater  
than 15%. SEF is read only.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
LEARNF—Learn Flag. LEARNF indicates that the current charge cycle can be used to learn the battery capacity.  
LEARNF is set when the active-empty point is detected. This occurs when the voltage register value drops below  
the VAE threshold AND the two previous current register values were negative and greater in magnitude than the  
IAE threshold. See the Active-Empty Point Detect section for additional information. LEARNF is cleared when any  
of the following occur:  
1) Learn cycle completes (CHGTF set).  
2) Current register value becomes negative indicating discharge current flow.  
3) ACR = 0  
4) ACR value is written or recalled from EEPROM.  
5) Sleep mode is entered.  
LEARNF is read only.  
UVF—Undervoltage Flag. UVF is set to indicate that the voltage measurement of the VIN pin is less than VUV, and  
must be written to a 0 to allow subsequent undervoltage events to be reported. UVF is not cleared internally.  
Writing UVF to 0 is effective only when VIN is greater or equal to VUV, otherwise, UV remains set due to the  
persistent undervoltage condition. UVF is set on power-up.  
PORF—Power-On Reset Flag. PORF is set to indicate initial power-up. PORF is not cleared internally. The user  
must write this flag value to a 0 to use it to indicate subsequent power-up events. If PORF indicates a power-on  
reset, the ACR could be misaligned with the actual battery state of charge. The system can request a charge to full  
to synchronize the ACR with the battery charge state. PORF is read/write-to-zero.  
X—Reserved Bits.  
RESULT REGISTERS  
The DS2784 processes measurement and cell characteristics on a 3.5s interval and yields seven result registers.  
The result registers are sufficient for direct display to the user in most applications. The host system can produce  
customized values for system use or user display by combining measurement, result and user EEPROM values.  
FULL(T) [ ]—The full capacity of the battery at the present temperature is reported normalized to the 40°C full  
value. This 15-bit value reflects the cell model Full value at the given temperature. FULL(T) reports values between  
100% and 50% with a resolution of 61ppm (precisely 2-14). The register is clamped to a maximum value of 100%  
even though the register format permits values greater than 100%.  
Active Empty, AE(T) [ ]—The active-empty capacity of the battery at the present temperature is reported  
normalized to the 40°C full value. This 13-bit value reflects the cell model active-empty value at the given  
temperature. AE(T) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2-14).  
Standby Empty, SE(T) [ ]—The standby-empty capacity of the battery at the present temperature is reported  
normalized to the 40°C full value. This 13-bit value reflects the cell model standby-empty value at the current  
temperature. SE(T) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2-14).  
Remaining Active Absolute Capacity (RAAC) [mAh]—RAAC reports the remaining battery capacity available  
under the current temperature conditions to the active-empty point in absolute units of milliamp-hours (mAhr).  
RAAC is 16 bits.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
MSB—ADDRESS 02h LSB—ADDRESS 03h  
215 214 213 212 211 210 29  
MSb  
28  
27  
26  
25  
24  
23  
22  
21 20  
LSb  
LSb  
MSb  
Units:  
1.6mAhr  
Remaining Standby Absolute Capacity (RSAC) [mAh]—RSAC reports the remaining battery capacity available  
under the current temperature conditions to the standby-empty point capacity in absolute units of milliamp-hours  
(mAhr). RSAC is 16 bits.  
MSB—ADDRESS 04h  
LSB—ADDRESS 05h  
25 24 23 22  
215 214 213 212 211 210 29  
MSb  
28  
27  
26  
21 20  
LSb  
LSb  
MSb  
Units:  
1.6mAhr  
Remaining Active Relative Capacity (RARC) [%]—RARC reports the remaining battery capacity available under  
the current temperature conditions to the active-empty point in relative units of percent. RARC is 8 bits.  
ADDRESS 06h  
27  
26  
25  
24  
23  
22  
21  
20  
MSb  
LSb  
Units:  
1%  
Remaining Standby Relative Capacity (RSRC) [%]—RSRC reports the remaining battery capacity available  
under the current temperature conditions to the standby-empty point capacity in relative units of percent. RSRC is 8  
bits.  
ADDRESS 07h  
27  
26  
25  
24  
23  
22  
21  
20  
MSb  
LSb  
Units:  
1%  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Calculation of Results  
RAAC [mAh] = (ACR[mVh] - AE(T) * FULL40[mVh]) * RSNSP [mhos]  
Note: RSNSP = 1/RSNS  
RSAC [mAh] = (ACR[mVh] - SE(T) * FULL40[mVh]) * RSNSP [mhos]  
Note: RSNSP = 1/RSNS  
RARC [%] = 100% * (ACR[mVh] - AE(T) * FULL40[mVh]) /  
{(AS * FULL(T) - AE(T)) * FULL40[mVh]}  
RSRC [%] = 100%* (ACR[mVh] - SE(T) * FULL40[mVh]) /  
{(AS * FULL(T) - SE(T)) * FULL40[mVh]}  
SPECIAL FEATURE REGISTER FORMAT  
All register bits are read and write accessible, with default values specified in each bit definition.  
ADDRESS 15H  
BIT 7  
X
BIT 6  
X
BIT 5  
X
BIT 4  
X
BIT 3  
X
BIT 2  
X
BIT 1  
X
BIT 0  
PIOB  
PIOB—PIO Pin Sense and Control Bit. Writing a 0 to the PIOB bit activates the PIO pin open-drain output driver,  
forcing the PIO pin low. Writing a 1 to PIOB disables the output driver, allowing the PIO pin to be pulled high or  
used as an input. Reading PIOB returns the logic level forced on the PIO pin. Note that if the PIO pin is high  
impedance/unconnected with PIOB set, a weak pulldown current source pulls the PIO pin to VSS. PIOB is set to a 1  
on power-up. PIOB is also set in Sleep mode to ensure the PIO pin is high-impedance in sleep mode.  
Note: Do not write PIOB to 0 if PSPIO is enabled.  
X—Reserved Bits.  
EEPROM REGISTER  
The EEPROM register provides access control of the EEPROM blocks. EEPROM blocks can be locked to prevent  
alteration of data within the block. Locking a block disables write access to the block. Once a block is locked, it  
cannot be unlocked. Read access to EEPROM blocks is unaffected by the lock/unlock status.  
EEPROM REGISTER FORMAT  
ADDRESS 1Fh  
BIT 7  
EEC  
BIT 6  
BIT 5  
X
BIT 4  
X
BIT 3  
X
BIT 2  
X
BIT 1  
BL1  
BIT 0  
BL0  
LOCK  
EEC—EEPROM Copy Flag. A 1 in this read-only bit indicates that a Copy Data Function command is in progress.  
While this bit is high, writes to EEPROM addresses are ignored. A 0 value in this bit indicates that data can be  
written to unlocked EEPROM.  
LOCK—EEPROM Lock Enable. When the lock bit is 0, the Lock Function command is ignored. Writing a 1 to this  
bit enables the Lock Function command. After setting the lock bit the Lock Function command must be issued as  
the next command, or else the lock bit is reset to 0. After the lock operation is completed, the lock bit is reset to 0.  
The lock bit is a volatile R/W bit, initialized to 0 upon POR.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
BL1—Parameter EEPROM Block 1 Lock Flag. A 1 in this read-only bit indicates that EEPROM block 1 (addresses  
60h to 7Fh) is locked (read only) while a 0 indicates block 1 is unlocked (read/write).  
BL0—User EEPROM Block 0 Lock Flag. A 1 in this read-only bit indicates that EEPROM block 0 (addresses 20h to  
2Fh is locked (read only) while a 0 indicates block 0 is unlocked (read/write).  
X – Reserved Bits.  
MEMORY  
The DS2784 has a 256-byte linear memory space with registers for instrumentation, status, and control, as well as  
EEPROM memory blocks to store parameters and user information. Byte addresses designated as “Reserved”  
typically return FFh when read. These bytes should not be written. Several byte registers are paired into two-byte  
registers in order to store 16-bit values. The most significant byte (MSB) of the 16-bit value is located at the even  
address and the least significant byte (LSB) is located at the next address (odd) byte. When the MSB of a two-byte  
register is read, the MSB and LSB are latched simultaneously and held for the duration of the Read Data  
command. This prevents updates to the LSB during the read ensuring synchronization between the two register  
bytes. For consistent results, always read the MSB and the LSB of a two-byte register during the same read data  
sequence.  
EEPROM memory consists of nonvolatile (NV) EEPROM cells overlaying volatile shadow RAM. The read data and  
write data protocols allow the 1-Wire interface to directly accesses the shadow RAM only. The Copy Data and  
Recall Data Function commands transfer data between the EEPROM cells and the shadow RAM. In order to  
modify the data stored in the EEPROM cells, data must be written to the shadow RAM and then copied to the  
EERPOM. To verify the data stored in the EEPROM cells, the EEPROM data must be recalled to the shadow RAM  
and then read from the shadow. After issuing the Copy Data Function command, access to the EEPROM block is  
not available until the EEPROM copy completes, which takes 2ms typically (see tEEC in the Electrical Characteristics  
table).  
Figure 6. EEPROM Access via Shadow RAM  
COPY  
EEPROM  
WRITE  
SERIAL  
INTERFACE  
RECALL  
SHADOW RAM  
READ  
USER EEPROM—BLOCK 0  
A 16-byte user EEPROM memory (block 0, addresses 20h–2Fh) provides NV memory that is uncommitted to other  
DS2784 functions. Accessing the user EEPROM block does not affect the operation of the DS2784. User EEPROM  
is lockable; once locked, write access is not allowed. The battery pack or host system manufacturer can program  
lot codes, date codes, and other manufacturing or warranty or diagnostic information and then lock it to safeguard  
the data. User EEPROM can also store parameters for charging to support different size batteries in a host device  
as well as auxiliary model data such as time to full charge estimation parameters.  
PARAMETER EEPROM—BLOCK 1  
Model data for the cells, as well as application operating parameters, are stored in the parameter EEPROM (block  
1, addresses 60h–7Fh). The ACR (MSB and LSB) and AS registers are automatically saved to EEPROM when the  
RARC result crosses 4% boundaries. This allows the DS2784 to be located outside the protection FETs.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Table 7. Parameter EEPROM Memory Block  
ADDRESS  
(HEX)  
ADDRESS  
(HEX)  
DESCRIPTION  
DESCRIPTION  
AE Segment 4 Slope  
CONTROL—Control Register  
AB— Accumulation Bias  
AC—Aging Capacity MSB  
AC—Aging Capacity LSB  
VCHG—Charge Voltage  
IMIN—Minimum Charge Current  
VAE—Active-Empty Voltage  
IAE—Active-Empty Current  
Active Empty 40  
60  
61  
62  
63  
64  
65  
66  
67  
68  
69  
70  
71  
72  
73  
74  
75  
76  
77  
78  
79  
AE Segment 3 Slope  
AE Segment 2 Slope  
AE Segment 1 Slope  
SE Segment 4 Slope  
SE Segment 3 Slope  
SE Segment 2 Slope  
SE Segment 1 Slope  
RSGAIN—Sense Resistor Gain MSB  
RSGAIN—Sense Resistor Gain LSB  
RSNSP—Sense Resistor Prime  
RSTC—Sense Resistor Temp  
Coefficient  
6A  
Full 40 MSB  
7A  
COB—Current Offset Bias  
6B  
6C  
6D  
6E  
6F  
Full 40 LSB  
7B  
7C  
7D  
7E  
7F  
TBP34  
Full Segment 4 Slope  
Full Segment 3 Slope  
Full Segment 2 Slope  
Full Segment 1 Slope  
TBP23  
TBP12  
Protector Threshold Register  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Table 8. Memory Map  
ADDRESS (HEX)  
DESCRIPTION  
READ/WRITE  
00  
01  
Protection Register  
Status Register  
RAAC MSB  
RAAC LSB  
RSAC MSB  
RSAC LSB  
RARC  
R/W  
R/W  
R
02  
03  
R
04  
R
05  
R
06  
R
07  
RSRC  
R
08  
Average Current Register MSB  
Average Current Register LSB  
Temperature Register MSB  
Temperature Register LSB  
Voltage Register MSB  
Voltage Register LSB  
Current Register MSB  
Current Register LSB  
Accumulated Current Register MSB  
Accumulated Current Register LSB  
Accumulated Current Register LSB-1  
Accumulated Current Register LSB-2  
Age Scalar  
R
09  
R
0A  
R
0B  
R
0C  
R
0D  
R
0E  
R
0F  
R
10  
R/W *  
R/W *  
R
11  
12  
13  
R
14  
R/W *  
R/W  
R
15  
Special Feature Register  
Full MSB  
16  
17  
Full LSB  
R
18  
Active-Empty MSB  
R
19  
Active-Empty LSB  
R
1A  
Standby-Empty MSB  
Standby-Empty LSB  
R
1B  
R
1C to 1E  
1F  
Reserved  
EEPROM Register  
R/W  
R/W  
20 to 2F  
38 to 5F  
60 to 7F  
80 to AF  
B0  
User EEPROM, Lockable, Block 0  
Reserved  
Parameter EEPROM, Lockable, Block 1  
Reserved  
R/W  
Factory Gain RSGAIN MSB  
Factory Gain RSGAIN LSB  
Reserved  
R
B1  
R
B2 to FF  
* Register value is automatically saved to EEPROM during Active mode operation and recalled from EEPROM on  
power-up.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
AUTHENTICATION  
Authentication is performed using a FIPS-180-compliant SHA-1 one-way hash algorithm on a 512-bit message  
block. The message block consists of a 64-bit secret, a 64-bit challenge and 384 bits of constant data. Optionally,  
the 64-bit net address replaces 64 of the 384 bits of constant data used in the hash operation. Contact Maxim for  
details of the message block organization.  
The host and the DS2784 both calculate the result based on the mutually known secret. The result of the hash  
operation is known as the message authentication code (MAC) or message digest. The MAC is returned by the  
DS2784 for comparison to the host’s MAC. Note that the secret is never transmitted on the bus and thus cannot be  
captured by observing bus traffic. Each authentication attempt is initiated by the host system by providing a 64-bit  
random challenge by the Write Challenge command. The host then issues the compute MAC or compute MAC with  
ROM ID command. The MAC is computed per FIPS 180, and then returned as a 160-bit serial stream, beginning  
with the least significant bit.  
DS2784 AUTHENTICATION COMMANDS  
WRITE CHALLENGE [0Ch]. This command writes the 64-bit challenge to the DS2784. The LSB of the 64-bit data  
argument can begin immediately after the MSB of the command has been completed. If more than 64-bits are  
written, the final value in the challenge register will be indeterminate. The Write Challenge command must be  
issued prior to every Compute MAC or Compute Next Secret command for reliable results.  
COMPUTE MAC WITHOUT ROM ID [36h]. This command initiates a SHA-1 computation without including the  
ROM ID in the message block. Since the ROM ID is not used, this command allows the use of a master secret and  
MAC response independent of the ROM ID. The DS2784 computes the MAC in tSHA after receiving the last bit of  
this command. After the MAC computation is complete, the host must write 8 write-zero time slots and then issue  
160 read-time slots to receive the 20-byte MAC. See Figure 10 for command timing.  
COMPUTE MAC WITH ROM ID [35h]  
This command is structured the same as the compute MAC without ROM ID, except that the ROM ID is included in  
the message block. With the ROM ID unique to each DS2784 included in the MAC computation, the MAC is unique  
to each token. See White Paper 4: Glossary of 1-Wire SHA-1 Terms, for more information. See Figure 10 for  
command timing.  
SHA-1-related commands used while authenticating a battery or peripheral device are summarized in Table 9 for  
convenience. Four additional commands for clearing, computing, and locking of the secret are described in detail in  
the following section.  
Table 9. Authentication Function Commands  
COMMAND  
HEX  
FUNCTION  
Writes 64-bit challenge for SHA-1 processing. Required prior to  
issuing Compute MAC and Compute Next Secret commands.  
Write Challenge  
0C  
Compute MAC Without ROM ID  
and Return MAC  
Computes hash operation of the message block with logical 1s in  
place of the ROM ID. Returns the 160-bit MAC.  
36  
35  
Compute MAC With ROM ID and  
Return MAC  
Computes hash operation of the message block including the  
ROM ID. Returns the 160-bit MAC.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
SECRET MANAGEMENT FUNCTION COMMANDS  
CLEAR SECRET [5Ah]. This command sets the 64-bit secret to all 0s (0000 0000 0000 0000h). The host must  
wait tEEC for the DS2784 to write the new secret value to EEPROM. See Figure 13 for command timing.  
COMPUTE NEXT SECRET WITHOUT ROM ID [30h]. This command initiates a SHA-1 computation of the MAC  
and uses a portion of the resulting MAC as the next or new secret. The hash operation is performed with the  
current 64-bit secret and the 64-bit challenge. Logical 1s are loaded in place of the ROM ID. 64 bits of the output  
MAC are used as the new secret value. The host must allow tSHA after issuing this command for the SHA  
calculation to complete, then wait tEEC for the DS2784 to write the new secret value to EEPROM. See Figure 11 for  
command timing.  
COMPUTE NEXT SECRET WITH ROM ID [33h]. This command initiates a SHA-1 computation of the MAC and  
uses a portion of the resulting MAC as the next or new secret. The hash operation is performed with the current 64-  
bit secret, the 64-bit ROM ID and the 64-bit challenge. 64 bits of the output MAC are used as the new secret value.  
The host must allow tSHA after issuing this command for the SHA calculation to complete, then wait tEEC for the  
DS2784 to write the new secret value to EEPROM. See Figure 11 for command timing.  
LOCK SECRET [60h]. This command write protects the 64-bit secret to prevent accidental or malicious overwrite  
of the secret value. The secret value stored in EEPROM becomes “final”. The host must wait tEEC for the DS2784 to  
write the lock secret bit to EEPROM. See Figure 13 for command timing.  
Table 10. Secret Loading Function Commands  
COMMAND  
HEX  
FUNCTION  
Clear Secret  
5A  
Clears the 64-bit Secret to 0000 0000 0000 0000h.  
Compute Next Secret Without  
ROM ID  
Compute Next Secret With  
ROM ID  
30  
33  
Generates new global secret.  
Generates new unique secret.  
Lock Secret  
60  
Sets lock bit to prevent changes to the secret.  
1-Wire BUS SYSTEM  
The 1-Wire bus is a system that has a single bus master and one or more slaves. A multidrop bus is a 1-Wire bus  
with multiple slaves, while a single-drop bus has only one slave device. In all instances, the DS2784 is a slave  
device. The bus master is typically a microprocessor in the host system. The discussion of this bus system consists  
of five topics: 64-bit net address, CRC generation, hardware configuration, transaction sequence, and 1-Wire  
signaling.  
64-BIT NET ADDRESS (ROM ID)  
Each DS2784 has a unique, factory-programmed 1-Wire net address that is 64 bits in length. The term net address  
is synonymous with the ROM ID or ROM code terms used in the DS2502 and other 1-Wire documentation. The first  
eight bits of the net address are the 1-Wire family code (32h). The next 48 bits are a unique serial number. The last  
eight bits are a cyclic redundancy check (CRC) of the first 56 bits (see Figure 7). The 64-bit net address and the  
1-Wire I/O circuitry built into the device enable the DS2784 to communicate through the 1-Wire protocol detailed in  
this data sheet.  
Figure 7. 1-Wire Net Address Format  
8-BIT FAMILY  
8-BIT CRC  
MSb  
48-BIT SERIAL NUMBER  
CODE (32H)  
LSb  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
CRC GENERATION  
The DS2784 has an 8-bit CRC stored in the most significant byte of its 1-Wire net address. To ensure error-free  
transmission of the address, the host system can compute a CRC value from the first 56 bits of the address and  
compare it to the CRC from the DS2784.  
The host system is responsible for verifying the CRC value and taking action as a result. The DS2784 does not  
compare CRC values and does not prevent a command sequence from proceeding as a result of a CRC mismatch.  
Proper use of the CRC can result in a communication channel with a very high level of integrity.  
The CRC can be generated by the host using a circuit consisting of a shift register and XOR gates as shown in  
Figure 8, or it can be generated in software using the polynomial X8 + X5 + X4 + 1. Additional information about the  
Maxim 1-Wire CRC is available in Application Note 27: Understanding and Using Cyclic Redundancy Checks with  
Maxim iButton Products.  
In the circuit in Figure 8, the shift register bits are initialized to 0. Then, starting with the least significant bit of the  
family code, one bit at a time is shifted in. After the 8th bit of the family code has been entered, then the serial  
number is entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC  
value.  
Figure 8. 1-Wire CRC Generation Block Diagram  
INPUT  
MSb  
LSb  
XOR  
XOR  
XOR  
HARDWARE CONFIGURATION  
Because the 1-Wire bus has only a single line, it is important that each device on the bus be able to drive it at the  
appropriate time. To facilitate this, each device attached to the 1-Wire bus must connect to the bus with open-drain  
or tri-state output drivers. The DS2784 uses an open-drain output driver as part of the bidirectional interface  
circuitry shown in Figure 9. If a bidirectional pin is not available on the bus master, separate output, and input pins  
can be connected together.  
The 1-Wire bus must have a pullup resistor at the bus-master end of the bus. A value of between 2kand 5kis  
recommended. The idle state for the 1-Wire bus is high. If, for any reason, a bus transaction must be suspended,  
the bus must be left in the idle state to properly resume the transaction later. Note that if the bus is left low for more  
than tLOW0, slave devices on the bus begin to interpret the low period as a reset pulse, effectively terminating the  
transaction.  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Figure 9. 1-Wire Bus Interface Circuitry  
Vpullup  
(2.0 to 5.5V)  
Bus Master  
Device 1-Wire Port (DQ)  
4.7kΩ  
Rx  
Tx  
Rx  
0.2  
(typ)  
μ
A
Tx  
100 Ohm  
MOSFET  
Rx = Receive  
Tx = Transmit  
TRANSACTION SEQUENCE  
The protocol for accessing the DS2784 through the 1-Wire port is as follows:  
Initialization  
Net Address Command  
Function Command(s)  
Data Transfer (not all commands have data transfer)  
All transactions of the 1-Wire bus begin with an initialization sequence consisting of a reset pulse transmitted by the  
bus master, followed by a presence pulse simultaneously transmitted by the DS2784 and any other slaves on the  
bus. The presence pulse tells the bus master that one or more devices are on the bus and ready to operate. For  
more details, see the Net Address Commands section.  
NET ADDRESS COMMANDS  
Once the bus master has detected the presence of one or more slaves, it can issue one of the net address  
commands described in the following paragraphs. The name of each net address command (ROM command) is  
followed by the 8-bit op code for that command in square brackets.  
Read Net Address [33h]. This command allows the bus master to read the DS2784’s 1-Wire net address. This  
command can only be used if there is a single slave on the bus. If more than one slave is present, a data collision  
occurs when all slaves try to transmit at the same time (open drain produces a wired-AND result).  
Match Net Address [55h]. This command allows the bus master to specifically address one DS2784 on the 1-Wire  
bus. Only the addressed DS2784 responds to any subsequent function command. All other slave devices ignore  
the function command and wait for a reset pulse. This command can be used with one or more slave devices on  
the bus.  
Skip Net Address [CCh]. This command saves time when there is only one DS2784 on the bus by allowing the  
bus master to issue a function command without specifying the address of the slave. If more than one slave device  
is present on the bus, a subsequent function command can cause a data collision when all slaves transmit data at  
the same time.  
Search Net Address [F0h]. This command allows the bus master to use a process of elimination to identify the  
1-Wire net addresses of all slave devices on the bus. The search process involves the repetition of a simple three-  
step routine: read a bit, read the complement of the bit, then write the desired value of that bit. The bus master  
performs this simple three-step routine on each bit location of the net address. After one complete pass through all  
64 bits, the bus master knows the address of one device. The remaining devices can then be identified on  
additional iterations of the process. See Chapter 5 of the Book of iButton® Standards for a comprehensive  
discussion of a net address search, including an actual example (www.maxim-ic.com/iButtonBook).  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
FUNCTION COMMANDS  
After successfully completing one of the net address commands, the bus master can access the features of the  
DS2784 with any of the function commands described in the following paragraphs. The name of each function is  
followed by the 8-bit op code for that command in square brackets. The function commands are summarized below  
in Table 11.  
Read Data [69h, XX]. This command reads data from the DS2784 starting at memory address XX. The LSb of the  
data in address XX is available to be read immediately after the MSb of the address has been entered. Because  
the address is automatically incremented after the MSb of each byte is received, the LSb of the data at address  
XX + 1 is available to be read immediately after the MSb of the data at address XX. If the bus master continues to  
read beyond address FFh, data is read starting at memory address 00 and the address is automatically  
incremented until a reset pulse occurs. Addresses labeled “Reserved” in the memory map contain undefined data  
values. The Read Data command can be terminated by the bus master with a reset pulse at any bit boundary.  
Reads from EEPROM block addresses return the data in the shadow RAM. A Recall Data command is required to  
transfer data from the EEPROM to the shadow. See Table 7 for more details.  
Write Data [6Ch, XX]. This command writes data to the DS2784 starting at memory address XX. The LSb of the  
data to be stored at address XX can be written immediately after the MSb of address has been entered. Because  
the address is automatically incremented after the MSb of each byte is written, the LSb to be stored at address XX  
+ 1 can be written immediately after the MSb to be stored at address XX. If the bus master continues to write  
beyond address FFh, the data starting at address 00 is overwritten. Writes to read-only addresses, reserved  
addresses and locked EEPROM blocks are ignored. Incomplete bytes are not written. Writes to unlocked EEPROM  
block addresses modify the shadow RAM. A Copy Data command is required to transfer data from the shadow to  
the EEPROM. See Table 7 for more details.  
Copy Data [48h, XX]. This command copies the contents of the EEPROM shadow RAM to EEPROM cells for the  
EEPROM block containing address XX. Copy Data commands that address locked blocks are ignored. While the  
copy data command is executing, the EEC bit in the EEPROM register is set to 1 and writes to EEPROM  
addresses are ignored. Reads and writes to non-EEPROM addresses can still occur while the copy is in progress.  
The Copy Data command takes tEEC time to execute, starting on the next falling edge after the address is  
transmitted.  
Recall Data [B8h, XX]. This command recalls the contents of the EEPROM cells to the EEPROM shadow memory  
for the EEPROM block containing address XX.  
Lock [6Ah, XX]. This command locks (write protects) the block of EEPROM containing address XX. The lock bit in  
the EEPROM register must be set to 1 before the Lock command is executed. To help prevent unintentional locks,  
one must issue the Lock command immediately after setting the lock bit (EEPROM register, address 1Fh, bit 06) to  
a 1. If the lock bit is 0 or if setting the lock bit to 1 does not immediately precede the Lock command, the Lock  
command has no effect. The Lock command is permanent; a locked block can never be written again.  
iButton is a registered trademark of Maxim Integrated Products, Inc.  
36 of 43  
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Table 11. All Function Commands  
COMMAND  
HEX  
DESCRIPTION  
Writes 64-bit challenge for SHA-1 processing. Required  
immediately prior to all Compute MAC and Compute Next Secret  
commands.  
Write Challenge  
0C  
Compute MAC  
Without ROM ID and Return  
MAC  
Computes hash operation of message block with logical 1s in  
place of the ROM ID.  
36  
35  
Compute MAC  
With ROM ID and Return MAC  
Computes hash operation of message block using the ROM ID.  
Clear Secret  
5A  
30  
Clears the 64-bit secret to 0000 0000 0000 0000h.  
Generates new global secret.  
Compute Next Secret Without  
ROM ID  
Compute Next Secret With  
ROM ID  
33  
60  
Generates new unique secret.  
Lock Secret  
Read Data  
Write Data  
Copy Data  
Recall Data  
Sets lock bit to prevent changes to the secret.  
69, XX  
6C, XX  
48, XX  
B8, XX  
Reads data from memory starting at address XX.  
Writes data to memory starting at address XX.  
Copies shadow RAM data to EEPROM block containing address  
XX.  
Recalls EEPROM block containing address XX to RAM.  
Permanently locks the block of EEPROM  
containing address XX.  
Lock  
6A, XX  
8B  
Set Overdrive  
Clear Overdrive  
Reset  
Sets 1-Wire interface timings to overdrive.  
Sets 1-Wire interface timings to standard (factory default).  
Resets DS2784 (software POR).  
8D  
C4  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Table 12. Guide to Function Command Requirements  
ISSUE MEMORY  
ISSUE 00h  
BEFORE READ  
READ/WRITE  
TIME SLOTS  
COMMAND  
Write Challenge  
ADDRESS  
Write: 64  
Read: up to 160  
Compute MAC  
Yes  
Compute Next Secret  
Clear/Lock Secret, Set/Clear  
Overdrive  
Read Data  
8 bits  
Read: up to 2048  
Write Data  
8 bits  
8 bits  
Write: up to 2048  
Copy Data  
Recall Data  
Lock  
8 bits  
8 bits  
Reset  
Figure 10. Compute MAC Function Command  
tSHA  
1-Wire  
Reset  
SKIP ROM  
Cmd  
Up to 160 Read Time Slots  
(Read 20-Byte MAC)  
Wait for MAC  
Computation  
Presence  
Pulse  
Compute  
MAC  
8 Write 0  
Time Slots  
Cmd  
38 of 43  
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Figure 11. Compute Next Secret Function Command  
tSHA  
tEEC  
1-Wire  
Reset  
SKIP ROM  
Cmd  
Wait for MAC  
Computation  
Wait for  
EEPROM Programming  
Compute  
Next Secret  
Cmd  
Presence  
Pulse  
Figure 12. Copy Function Command  
tEEC  
1-Wire  
Reset  
SKIP ROM  
Cmd  
Copy  
Cmd  
Wait for  
EEPROM Programming  
8 Write  
Time Slots  
Presence  
Pulse  
Figure 13. Clear/Lock Secret, Set/Clear Overdrive Function Commands  
tEEC  
1-Wire  
Reset  
SKIP ROM  
Cmd  
Clear/Lock  
Secret Cmd  
or  
Wait for EEPROM Copy Time  
Presence  
Pulse  
Set/Clear  
Overdrive Cmd  
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DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
I/O SIGNALING  
The 1-Wire bus requires strict signaling protocols to ensure data integrity. The four protocols used by the DS2784  
are as follows: the initialization sequence (reset pulse followed by presence pulse), write 0, write 1, and read data.  
The bus master initiates all these types of signaling except the presence pulse.  
The initialization sequence required to begin any communication with the DS2784 is shown in Figure 14. A  
presence pulse following a reset pulse indicates that the DS2784 is ready to accept a net address command. The  
bus master transmits (Tx) a reset pulse for tRSTL. The bus master then releases the line and goes into Receive  
mode (Rx). The 1-Wire bus line is then pulled high by the pullup resistor. After detecting the rising edge on the DQ  
pin, the DS2784 waits for tPDH and then transmits the presence pulse for tPDL  
.
Figure 14. 1-Wire Initialization Sequence  
tRSTL  
tRSTH  
tPDH  
tPDL  
PACK+  
PACK-  
DQ  
LINE TYPE LEGEND:  
BUS MASTER ACTIVE LOW  
BOTH BUS MASTER AND  
DS2784 ACTIVE LOW  
DS2784 ACTIVE LOW  
RESISTOR PULLUP  
WRITE-TIME SLOTS  
A write-time slot is initiated when the bus master pulls the 1-Wire bus from a logic-high (inactive) level to a logic-low  
level. There are two types of write-time slots: write 1 and write 0. All write-time slots must be tSLOT in duration with a  
1µs minimum recovery time, tREC, between cycles. The DS2784 samples the 1-Wire bus line between tLOW1_MAX and  
tLOW0_MIN after the line falls. If the line is high when sampled, a write 1 occurs. If the line is low when sampled, a  
write 0 occurs. The sample window is illustrated in Figure 15. For the bus master to generate a write-1 time slot, the  
bus line must be pulled low and then released, allowing the line to be pulled high less than tRDV after the start of the  
write time slot. For the host to generate a write 0 time slot, the bus line must be pulled low and held low for the  
duration of the write-time slot.  
READ-TIME SLOTS  
A read-time slot is initiated when the bus master pulls the 1-Wire bus line from a logic-high level to a logic-low level.  
The bus master must keep the bus line low for at least 1µs and then release it to allow the DS2784 to present valid  
data. The bus master can then sample the data tRDV from the start of the read-time slot. By the end of the read-time  
slot, the DS2784 releases the bus line and allows it to be pulled high by the external pullup resistor. All read-time  
slots must be tSLOT in duration with a 1µs minimum recovery time, tREC, between cycles. See Figure 15 and the  
timing specifications in the Electrical Characteristics table for more information.  
40 of 43  
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
Figure 15. 1-Wire Write and Read-Time Slots  
WRITE 0 SLOT  
WRITE 1 SLOT  
tSLOT  
tLOW0  
tSLOT  
tLOW1  
VPULLUP  
tREC  
GND  
>1µs  
Device Sample Window  
MIN TYP MAX  
Device Sample Window  
MIN TYP  
MAX  
30µs  
3µs  
MODE  
15µs  
2µs  
15µs  
1µs  
30µs  
3µs  
15µs  
2µs  
15µs  
Standard  
1µs  
Overdrive  
READ DATA SLOT  
Data = 0  
tSLOT  
Data = 1  
tSLOT  
tREC  
VPULLUP  
tRDV  
tRDV  
GND  
>1µs  
Master Sample Window  
Master Sample Window  
MODE  
15µs  
2µs  
15µs  
2µs  
Standard  
Overdrive  
LINE TYPE LEGEND:  
Bus Master active LOW  
Device active LOW  
Resistor pullup  
Both Bus Master and Device  
active LOW  
41 of 43  
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
PACKAGE INFORMATION  
For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages.  
Note that a “+”, “#”, or “-“ in the package code indicates RoHS status only. Package drawings may show a different  
suffix character, but the drawing pertains to the package regardless of RoHS status.  
PACKAGE TYPE  
PACKAGE CODE  
OUTLINE NO.  
LAND PATTERN NO.  
14 TDFN-EP  
(3mm x 5mm)  
T1435N+1  
21-0253  
90-0246  
42 of 43  
DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication  
REVISION HISTORY  
REVISION  
DATE  
PAGES  
DESCRIPTION  
CHANGED  
Changed the VDD maximum operating range in the Electrical Characteristics  
table to 4.6V.  
2–4  
Added text in Note 3 of Table 1 for UV case where UVEN = 0 and to the  
Undervoltage section.  
Changed VDD to VIN for pin monitored for UV release condition.  
9
9
5/09  
Added “VIN pin is limited to VDD voltage” text in the Voltage Measurement  
section.  
13  
Added CC FET Turn Off, DC FET Turn Off, COC Delay, DOC Delay, SC Delay,  
OV Delay, UV Delay TOCs.  
5–8  
Added the CTG pin and connection to GND in the Typical Operating Circuit.  
Changed the DOCUMENT NO. to 21-0253 in the Package Information table.  
Corrected the “Top Mark” in the Ordering Information table.  
Deleted all references to CRC generation during any command sequences  
unrelated to 64-bit ID in the CRC Generation section  
9
41  
1
8/09  
4/10  
3/12  
34  
43 of 43  
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses  
are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.  
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600  
2012 Maxim Integrated Products  
Maxim is a registered trademark of Maxim Integrated Products, Inc.  

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