MAX1894 [MAXIM]
Advanced Li+ Battery-Pack Protectors; 先进的锂离子电池组保护
| 型号： | MAX1894 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Advanced Li+ Battery-Pack Protectors |
| 文件： | 总16页 (文件大小：307K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2278; Rev 0; 4/02
Advanced Li+ Battery-Pack Protectors
General Description
Features
The MAX1894/MAX1924 are lithium-ion/lithium-polymer
(Li+) battery-pack protector ICs for 3- or 4-series Li+ bat-
tery packs. The MAX1894/MAX1924 enhance the useful
operating life of Li+ batteries by monitoring individual cell
voltages and preventing over/undervoltage conditions.
The MAX1894/MAX1924 also protect the battery pack
against charge current, discharge current, and pack-
short fault conditions.
ꢀ Protect Against Cell Overvoltage
Factory Programmable Limits from 4V to 4.4V
Accurate to ±±.ꢀ5
ꢀ Protect Against Cell Undervoltage
Factory Programmable Limits from 2V to 3.2V
Accurate to ±2.±5
ꢀ Protect Against Charge, Discharge, and Pack-
In case of a fault condition, on-board drivers control
external P-channel MOSFETs, which disconnect the cells
from the pack external terminals. The external protection
MOSFETs are connected in a common-source configura-
tion that does not require external pullup resistors. The
MAX1894/MAX1924 use only one current-sense resistor
to achieve the protection features. All protection thresh-
olds and delays do not require any external components
and are trimmed at the factory.
Short Current Faults
ꢀ Automatically Trickle Charges Deeply Discharged
Cells
ꢀ Fully Integrated MOSFET Drivers Do Not Require
Pullup Resistors
ꢀ ±.8µA (typ) Shutdown Supply Current Prevents
Deep Discharge of Cells
ꢀ 3±µA (typ) Operating Supply Current
ꢀ 28V (max) Input Voltage
If any cell voltage drops below the undervoltage thresh-
old, the MAX1894/MAX1924 disconnect the pack from
the load and power down to prevent deep discharge of
the pack. The MAX1894/MAX1924 offer a trickle-charge
feature, which provides a low-current path to safely
charge a deeply discharged pack. The MAX1894/
MAX1924 also have two logic-level inputs, which can be
used by a microcontroller to disable the protection
MOSFETs and to put the device in shutdown. The
MAX1894/MAX1924 have low quiescent current (30µA
typ) and ultra-low shutdown current (0.8µA typ) to pre-
vent deep-cell discharge.
ꢀ Available in Small 16-Pin QSOP Package
Pin Configuration
TOP VIEW
B4P
1
2
3
4
5
6
7
8
16 SRC
15 DSO
V
CC
CGO
14
B3P
IC3
B2P
IC2
B1P
IC1
13 TKO
12 SHDN
11 CTL
10 PKN
The MAX1894X is designed for 4-series battery packs,
without hysteresis on the protection thresholds. The
MAX1924V and MAX1924X include hysteresis for the 3-
and 4-series packs, respectively.
MAX1894
MAX1924
9
BN
Applications
QSOP
3- or 4-Series Li+ Battery Packs
Ordering Information
OVERVOLTAGE
THRESHOLD HYSTERESIS
PART
TEMP RANGE
PIN-PACKAGE
CELLS
OVERVOLTAGE
MAX1894XEEE
MAX1924VEEE
MAX1924XEEE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
16 QSOP
16 QSOP
16 QSOP
4
3
4
4.25V*
4.35V*
4.35V*
No
Yes
Yes
*Contact factory for alternative threshold voltages.
Typical Applications Circuits appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Advanced Li+ Battery-Pack Protectors
ABSOLUTE MAXIMUM RATINGS
SRC, IC2, IC3, V
to BN.......................................-0.3V to +28V
PKN to BN ...................................................................-2V to +2V
ESD Protection on All Pins............................................... 2000V
CC
IC1 to BN..................................................................-0.3V to +6V
DSO, TKO, CGO to BN.............................-0.3V to (V + 0.3V)
Continuous Power Dissipation (T = +70°C)
SRC
A
B4P to B3P ...............................................................-0.3V to +6V
B3P to B2P ...............................................................-0.3V to +6V
B2P to B1P ...............................................................-0.3V to +6V
B1P to BN.................................................................-0.3V to +6V
CTL, SHDN to PKN...................................................-0.3V to +6V
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
= V
+ 0.1V, each battery cell voltage (V
) = 3.6V, V
= V
= V , T = ±°C to +8ꢀ°C, unless otherwise noted.
PKN A
SRC
B4P
CELL
CTL
SHDN
Typical values are at T = +25°C.)
A
PARAMETER
SYMBOL
CONDITIONS
= 1V
B_P
MIN
TYP
MAX
UNITS
SRC Input Current
V
- V
20
40
µA
SRC
Supply Current (Note 1)
Shutdown Supply Current
I
No faults
Undervoltage without charge source
30
45
2
µA
µA
SUP
I
0.8
SHDN
Top Cell Sampling Current
(Note 2)
V
V
= 3.6V
= 3.6V
60
500
4.5
µA
pA
V
CELL
CELL
Intermediate Cell Input Bias
Current (Note 3)
V
Undervoltage Lockout
CC
Rising edge, hysteresis = 1% falling edge
- V
Threshold
Charge-Mode Detection
Threshold
V
25
100
mV
SRC
B4P
MAX1894X cell voltage rising
4.225
4.325
4.250
4.350
4.275
4.375
Overvoltage Threshold (Note 4)
V
V
OV_TH
MAX1924X, MAX1924V cell voltage rising
Overvoltage Threshold
Hysteresis
V
MAX1924X, MAX1924V cell voltage falling
Cell voltage falling
200
2.300
145
mV
V
OV_HYT
Undervoltage Threshold (Note 4)
V
2.260
130
2.340
160
UV_TH
PKN to BN Discharge Current
Fault Threshold
V
mV
OD_TH
PKN to BN Charge Current
Fault Threshold
V
-120
385
-100
405
-80
mV
mV
OC_TH
PKN to BN Discharge Current
Fault Threshold, Pack-Short
Condition
V
425
PS_TH
Discharge or Charge Current
Fault to DSO, CGO, TKO
Transition Delay Time
Discharge Current Fault to DSO
Transition Time Delay for Pack-
Short Condition
t
2.5
3
3.5
ms
µs
I-DELAY
t
400
450
500
P-DELAY
2
_______________________________________________________________________________________
Advanced Li+ Battery-Pack Protectors
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
+ 0.1V, each battery cell voltage (V
) = 3.6V, V
= V
= V , T = 0°C to +85°C, unless otherwise noted.
PKN A
SRC
B4P
CELL
CTL
SHDN
Typical values are at T = +25°C.)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Charge-Voltage Comparator
Threshold for Resetting
V
- V
B4P
25
100
mV
SRC
Discharge-Current Fault Latch
Discharge-Voltage Comparator
Threshold for Resetting Charge-
Current Fault Latch
V
V
- V
25
100
mV
B4P
SRC
SRC
DSO, CGO, and TKO Sink
Current
= 12V, V
= 12V, V
= 5V (Note 5)
= 10V
100
3.5
200
5
µA
mA
ms
PIN
PIN
DSO, CGO, and TKO
Source Current
V
V
SRC
CTL
= 3V (Note 5)
Under/Overvoltage to DSO,
CGO, TKO Transition Delay
t
270
2.4
320
370
V-DELAY
SHDN, CTL Input High (Note 6)
SHDN, CTL Input Low (Note 6)
Rising edge
Falling edge
V
V
1.2
1
SHDN, CTL Input Leakage
Current
PKN = BN
µA
ns
V
SHDN, CTL Delay to Output
Change
50
-0.1
-14
DSO, CGO, TKO Output High
(Note 7)
V
V
= 4V, V
= 4V
= 3V
CTL
B_P
B_P
DSO, CGO, TKO Output Low
(Note 7)
V
_______________________________________________________________________________________
3
Advanced Li+ Battery-Pack Protectors
ELECTRICAL CHARACTERISTICS
(V
= V
+ 0.1V, each battery cell voltage (V
) = 3.6V, V
= V
= V , T = -40°C to +85°C, unless otherwise noted.)
PKN A
SRC
B4P
CELL
CTL
SHDN
PARAMETER
SYMBOL
CONDITIONS
= 1V
MIN
TYP
MAX
40
UNITS
µA
SRC Input Current
V
- V
SRC B_P
Supply Current (Note 1)
Shutdown Supply Current
I
No faults
Undervoltage without charge source
50
µA
SUP
I
2
µA
SHDN
Charge-Mode Detection
Threshold
V
- V
25
100
mV
V
SRC
B4P
MAX1894X cell voltage rising
MAX1924X, MAX1924V cell voltage rising
Cell voltage falling
4.21
4.32
2.24
4.29
4.38
2.36
Overvoltage Threshold (Note 4)
V
V
OV_TH
Undervoltage Threshold (Note 4)
V
UV_TH
OD_TH
PKN to BN Discharge-Current
Fault Threshold
V
V
120
170
-70
mV
PKN to BN Charge-Current
Fault Threshold
-130
mV
mV
OC_TH
PKN to BN Discharge-Current
Fault Threshold, Pack Short
Condition
Discharge- or Charge-Current
Fault to DSO, CGO, TKO
Transition Delay Time
Discharge-Current Fault to DSO
Transition Time Delay for Pack
Short Condition
Charge-Voltage Comparator
Threshold for Resetting
V
345
2
465
4
PS_TH
t
ms
µs
I-DELAY
t
370
25
25
480
100
100
P-DELAY
V
- V
- V
mV
mV
SRC
B4P
Discharge-Current Fault Latch
Discharge-Voltage Comparator
Threshold for Resetting Charge-
Current Fault Latch
V
V
B4P
SRC
SRC
DSO, CGO, and TKO Sink
Current
= 12V, V
= 12V, V
= 5V (Note 5)
= 10V
100
3.5
µA
mA
ms
PIN
PIN
DSO, CGO, and TKO
Source Current
V
V
SRC
CTL
= 3V (Note 5)
Under/Overvoltage to DSO,
CGO, TKO Transition Delay
t
270
2.4
370
1.2
V-DELAY
SHDN, CTL Input High (Note 6)
SHDN, CTL Input Low (Note 6)
Rising edge
Falling edge
V
V
Note 1: Average current from the top of the battery pack. Measured at V
.
CC
Note 2: Typical supply current for the top cell during the 0.5ms sampling period.
Note 3: Input bias current for this measurement is valid when all cell voltages are equal and the measurement is made over a time
greater than 3 seconds.
Note 4: Each cell voltage is sampled individually and a differential measurement is made (V
- V
, V
B3P B3P
- V
, V
B2P B2P
- V
,
B1P
B4P
and V
- BN).
B1P
Note 5: V
represents V
, V
, or V
.
TKO
PIN
DSO CGO
Note 6: Inputs to SHDN and CTL pins are referred to PKN.
Note 7: Measurements are with respect to V
.
SRC
4
_______________________________________________________________________________________
Advanced Li+ Battery-Pack Protectors
Typical Operating Characteristics
(T = +25°C, unless otherwise noted.)
A
SUPPLY CURRENT
vs. TEMPERATURE
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
UNDERVOLTAGE THRESHOLD
vs. TEMPERATURE
50
40
30
20
10
0
1.2
2.310
2.305
2.300
4-SERIES BATTERY PACK
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
4-SERIES BATTERY PACK
B1P
B3P
B4P
B2P
2.295
2.290
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
CHARGE-CURRENT FAULT
THRESHOLD vs. TEMPERATURE
CHARGE-CURRENT FAULT RECOVERY
THRESHOLD vs. TEMPERATURE
OVERVOLTAGE THRESHOLD
vs. TEMPERATURE
100
90
80
70
60
50
40
30
20
130
120
110
100
90
4.360
4.355
4.350
4.345
4.340
MAX1924X
B1P
B3P
B4P
B2P
80
70
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
DISCHARGE-CURRENT FAULT THRESHOLD
vs. TEMPERATURE
DISCHARGE-CURRENT FAULT RECOVERY
THRESHOLD vs. TEMPERATURE
PACK-SHORT CURRENT FAULT
THRESHOLD vs. TEMPERATURE
155
150
145
140
135
100
90
80
70
60
50
40
30
20
415
410
405
400
395
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
_______________________________________________________________________________________
5
Advanced Li+ Battery-Pack Protectors
Typical Operating Characteristics (continued)
(T = +25°C, unless otherwise noted.)
A
DISCHARGE-CURRENT FAULT TIMING
CHARGE-CURRENT FAULT TIMING
PACK-SHORT CURRENT FAULT TIMING
MAX1894 toc10
MAX1894 toc11
MAX1894 toc12
0
V
- V
V
- V
BN
PKN BN
200mV/div
PKN
100mV/div
V
- V
BN
PKN
100mV/div
0
0
DSO
5V/div
DSO
5V/div
CGO
5V/div
0
0
0
1ms/div
1ms/div
100µs/div
Pin Description
PIN
NAME
B4P
FUNCTION
1
Cell 4 Positive Connection. Short B4P to B3P for MAX1924V.
Supply Input. Connect this pin to the top of the battery pack through a diode and a capacitor
(see the Typical Application Circuit).
2
V
CC
3
4
5
6
7
8
B3P
IC3
B2P
IC2
B1P
IC1
Cell 3 Positive Connection
Internal Connection. Float this pin.
Cell 2 Positive Connection
Internal Connection. Float this pin.
Cell 1 Positive Connection
Internal Connection. Float this pin.
Battery Negative. Connection for the cell 1 negative terminal and the top of the current-sense
9
BN
PKN
CTL
resistor R . BN is also chip ground.
SENSE
10
11
Pack Negative. The sense resistor (R ) is connected between BN and PKN.
SENSE
Control Input. Drive CTL low for normal operation. Drive CTL high to turn off the three external
protection MOSFETs.
Shutdown. Drive SHDN low for normal operation. Drive SHDN high to put the device into shutdown
if no charger is present.
12
13
14
15
16
SHDN
TKO
Trickle-Charge Driver Output. TKO drives the gate of an external P-channel trickle-charge MOSFET
low (on) in normal operation.
Fast-Charge Driver Output. CGO drives the gate of an external P-channel fast-charge MOSFET low
(on) in normal operation.
CGO
DSO
SRC
Discharge Driver Output. DSO drives the gate of an external P-channel discharge control MOSFET
low (on) in normal operation.
Common Source Connection for MOSFETs. SRC provides the bias for gate drivers DSO, TKO,
and CGO.
6
_______________________________________________________________________________________
Advanced Li+ Battery-Pack Protectors
Detailed Description
Table 1. Flow Chart Symbol Table
The MAX1894/MAX1924 battery-pack protectors super-
vise the charging and discharging process of Li+ cells.
Designed for 3-series (MAX1924V) and 4-series
(MAX1894X/MAX1924X) applications, these devices
monitor the voltage across each cell to provide protec-
tion against undervoltage, overvoltage, and
overcurrent damage.
SYMBOL
DESCRIPTION
Charge-Current Fault Threshold
(Negative Value)
V
V
OC_TH
OD_TH
Discharge-Current Fault Threshold
Pack-Short Discharge-Current Fault
Threshold
V
V
PS_TH
Output pins CGO, TKO, and DSO control external
MOSFET gates. These MOSFETs, in turn, control the
fast-charging, trickle-charging, and discharge process-
es of the battery pack (Figure 1).
Undervoltage Threshold
UV_TH
OV_TH
V
Overvoltage Threshold
V
MOSFET Common Source Voltage
Sense Resistor Voltage
SRC
V
V
RSENSE
OV_HYT
OVF
Modes of Operation
Overvoltage Threshold Hysteresis
Overvoltage Sample Counter
Undervoltage Sample Counter
Shutdown Mode
The MAX1894/MAX1924 go into shutdown mode under
two conditions: the SHDN pin is driven high without a
charger applied, or a battery cell undervoltage fault is
detected, also without a charger applied. In shutdown
UVF
are returned to the normal low state (see Figure 3). The
MAX1924 also includes a hysteresis of 200mV.
mode, the device consumes 0.8µA (typ) on the V
pin
CC
The overvoltage threshold is preprogrammed and
requires no external components. The overvoltage thresh-
old is factory set at 4.25V (typ) for the MAX1894 and
4.35V (typ) for the MAX1924. Contact Maxim for more
information on threshold levels between 4V and 4.4V.
and all MOSFETs are off. The MAX1894/MAX1924 stay
in shutdown mode as long as no charging voltage is
applied to the battery pack (V
is less than the pack
SRC
voltage). When the battery pack is connected to a
charger (V > V + 0.1V) and the pack voltage is
SRC
B4P
above 4.5V, the device goes into normal operating
mode and begins monitoring the pack (see Figure 2).
Undervoltage Protection
The MAX1894/MAX1924 provide undervoltage protec-
tion to avoid overdischarging the cells. With no battery
charger present, and an undervoltage fault is detected
in four consecutive samples, DSO, CGO, and TKO go
high and the device goes into shutdown mode (see
Figure 4).
Normal Mode
In the normal mode of operation, the MAX1894/MAX1924
are in either a standby mode (29µA typ) or sample mode
(160µA typ). The device enters the standby mode from
shutdown mode. The standby mode lasts for 79ms; then
the device goes into the sample mode. During sample
mode, the MAX1894/MAX1924 check each cell for over-
voltage and undervoltage. Sample mode lasts for 0.5ms;
then the MAX1894/MAX1924 return to standby mode.
During sample mode, the MAX1894/MAX1924 do not intro-
duce cell mismatch.
If a battery charger is applied to the battery pack and
one or more cells are below V
, then only TKO
UV_TH
goes low, allowing trickle-charge current to flow. If no
undervoltage is detected in any sample, DSO, CGO,
and TKO all go low.
The undervoltage threshold is preprogrammed at 2.30V
(typ). Contact Maxim for more information on threshold
levels between 2V and 3.2V.
During normal mode operation, the MAX1894/MAX1924
continuously monitor the voltage across R
for charge
SENSE
or discharge current faults, or battery pack-short faults.
Charge-Current Fault Protection
The MAX1894/MAX1924 protect against excessive
charge current by monitoring the voltage developed
Protection Features
Overvoltage Protection
The MAX1894/MAX1924 provide overvoltage protection
to avoid overcharging cells. When an overvoltage fault
is detected in four consecutive samples, CGO and TKO
go high, stopping the charging process. The
MAX1894/MAX1924 continue to sample the cell volt-
ages, and if no overvoltage is detected, CGO and TKO
across R
. R
is connected between BN and
exceeds the charge-current fault
, typically 100mV) for more than 3ms,
SENSE SENSE
PKN. If V
RSENSE
threshold (V
OC_TH
the charge current comparator is tripped, setting CGO
and TKO high.
The charge-current fault condition is latched and is not
reset until the MAX1894/MAX1924 detect a reversal in
_______________________________________________________________________________________
7
Advanced Li+ Battery-Pack Protectors
OVERDISCHARGE
PROTECTION
R5
10Ω
C5
2.2µF
PACK +
TRICKLE
CHARGE
16
SRC
BN
15
DSO
OVERCHARGE
PROTECTION
14
13
CGO
TKO
R
TKO
510Ω
D1
CMPSH-3
2
1
V
CC
B4P
C6
0.1µF
R4
51Ω
MAX1894X
MAX1924X
C4
R3
1µF
1kΩ
3
4
B3P
IC3
C3
0.1µF
R2
1kΩ
5
6
B2P
IC2
12
11
SHDN
CTL
MICRO-
CONTROLLER
C2
0.1µF
R1
1kΩ
7
B1P
C1
0.1µF
8
9
IC1
BN
PKN
10
R
SENSE
0.02Ω
PACK -
Figure 1. Typical Applications Circuit with Trickle Charge
the direction of current flow. To reverse the current flow,
the charger has to be removed (Figure 5). The sustain-
ing condition for the latch is a 100mV (max) voltage
drop across SRC and B4P. Since the charge-current
fault threshold between BN and PKN is also 100mV
than 3ms, the discharge-current comparator is tripped,
setting DSO, CGO, and TKO high.
Discharge-current fault is latched and is not reset until
the MAX1894/MAX1924 detect a reversal in the direc-
tion of current flow. To reverse the current flow, a
charger must be applied (Figure 6).
(typ), the R
of the overcharge protection MOSFET
DS_ON
must be greater than the sense resistor in order to
ensure a latched state.
Pack-Short Current Fault Protection
The MAX1894/MAX1924 protect against a shorted
pack by monitoring the voltage developed across
Discharge-Current Fault Protection
The MAX1894/MAX1924 protect against excessive dis-
charge-current by monitoring the voltage developed
R
. If V
PS_TH
exceeds the pack-short threshold
RSENSE
SENSE
(V
, typically 405mV) for more than 450µs, the
across R
. If V
exceeds the discharge-cur-
OD_TH
SENSE
rent fault threshold (V
RSENSE
pack-short comparator is tripped, setting CGO, DSO,
and TKO high.
, typically 145mV) for more
8
_______________________________________________________________________________________
Advanced Li+ Battery-Pack Protectors
V
= 2.3V typ &
OV_TH
UV_TH
V
= 4.25V typ
SHUTDOWN PIN
OPERATION
SHUTDOWN
DSO, CGO, TKO = H
NORMAL OPERATION
NO
NO
V
> V
B4P
SRC
+ 0.1V
YES
TKO = L
NO
NO
SHDN = H
YES
V
> 4.5V
CC
YES
STANDBY = 79ms
SHUTDOWN
DSO, CGO,
TKO = H
NO
NO
V
> V + 0.1V
B4P
SRC
V
< V
UV_TH
CELL
YES
LATCH UVF = UVF + 1
RESET UVF
RESET OVF
YES
V
> V
CELL
OV_TH
DSO, CGO, TKO = H
YES
LATCH OVF = OVF + 1
MAX1924 V
= 200mV
OV_HYT
OV_HYT
MAX1894 V
CONTROL PIN
OPERATION
= 0
YES
OVF = 4
NO
TKO, CGO = H
NORMAL OPERATION
RESET V
= 4.25V typ
OV_TH
NO
NO
UVF = 4
YES
CTL = H
YES
DSO, CGO, TKO = H
V
> V + 0.1V
B4P
SRC
NO
YES
CGO = DSO = H
Figure 2. Undervoltage and Overvoltage Protection Flow Chart
Figure 3. Shutdown and Control Pin Flow Charts
Pack-short current fault is latched and is not reset until
the MAX1894/MAX1924 detect a reversal in the direc-
tion of current flow. A charger must be applied to
reverse the current flow (Figure 7).
Design Procedure
Fast and Trickle-Charge Paths
The MAX1894/MAX1924 offer the designer the flexibility
of two charging paths: a fast charging path and a trick-
le-charge path (see Figure 1). Trickle charging is
enabled and TKO is set low when one or more cells are
belows V
.
UV_TH
_______________________________________________________________________________________
9
Advanced Li+ Battery-Pack Protectors
UNDERVOLTAGE CONDITION
320ms
UNDERVOLTAGE THRESHOLD
CELL VOLTAGE
SAMPLING
DSO, CGO, TKO
OVERVOLTAGE CONDITION (MAX1894, NO HYSTERESIS)
320ms
80ms
OVERVOLTAGE THRESHOLD
CELL VOLTAGE
SAMPLING
TKO, CGO
OVERVOLTAGE CONDITION (MAX1894, WITH HYSTERESIS)
320ms
OVERVOLTAGE THRESHOLD
CELL VOLTAGE
OVERVOLTAGE THRESHOLD HYSTERESIS
SAMPLING
TKO, CGO
Figure 4. Undervoltage and Overvoltage Timing Diagrams
10 ______________________________________________________________________________________
Advanced Li+ Battery-Pack Protectors
NORMAL OPERATION
NORMAL OPERATION
OD FAULT
RSENSE
FOR 3ms
OC FAULT
NO
NO
V
> V
OD_TH
V
< V
RSENSE
OC_TH
FOR 3ms
YES
YES
DSO, TKO, CGO = H
TKO, CGO = H
NO
YES
NO
YES
V
> V + 0.1V
B4P
SRC
V
> V
+ 0.1V
SRC
B4P
Figure 5. Charge-Current Fault
Figure 6. Discharge-Current Fault
Set the nominal values of the trickle charge current by
R
Selection
SENSE
selecting resistor R
based on the following equation:
All current faults are detected using a current-sense
resistor connected between BN and PKN. The value of
this resistor sets the fault current levels. Charge-current
fault is given by:
TKO
R
= (V
- VP )/I
ACK TKO
TKO
CHRG
where V
the battery-pack voltage, and I
current.
is the charger output voltage, V
is
PACK
CHRG
is the trickle-charge
TKO
V
100mV
R
SENSE
OC_TH
I
=
=
OC_TH
When the trickle-charge option is not used, float CGO
and connect TKO to the gate of the overcharge protec-
tion MOSFET (see Figure 9). When a charger is applied
and the voltage on one or more cells is less than
R
SENSE
Discharge-current fault is given by:
V
, the MAX1894/MAX1924 modulate the TKO out-
UV_TH
V
145mV
R
SENSE
OC_TH
I
=
=
put until all cells exceed V
.
UV_TH
OD_TH
R
SENSE
Protection FET Drivers
All three external MOSFETs have their source pins con-
nected to the SRC pin. When a MOSFET is turned off, FET
drivers pull the gate to the SRC voltage. Additional exter-
nal pullup resistors are not needed. When the MOSFET is
Pack-short current fault is given by:
V
405mV
R
SENSE
PS_TH
I
=
=
PS_TH
R
SENSE
turned on, the V
is limited to -14V by a clamp circuit
GS
built in the drivers. This allows use of MOSFETs with maxi-
Select R
to obtain the desired fault current levels.
SENSE
For example, a 20mΩ R
mum V of -20V. All three drivers have the same circuit-
GS
sets the charge current
that can withstand the
SENSE
SENSE
ry and drive capability. The quiescent current in normal
operation is less than 3µA per driver.
fault at 5A. Choose an R
dissipation during normal operation and current fault
conditions. For example, pack-short current is given by:
______________________________________________________________________________________ 11
Advanced Li+ Battery-Pack Protectors
Table 2. State Table
SHDN
STATE
CHARGER
APPLIED
GOES INTO
SHUTDOWN MODE
STATE
CTL STATE
TKO
CGO
DSO
L
L
L
L
L
L
L
L
L
L
Yes
No
X
No
Yes
No
No
No
L
H
H
H
H
H
H
H
L
Undervoltage
H
H
H
H
Overvoltage
Charge Current Fault
Discharge Current Fault
Yes
No
L
H
Pack Short Current
Fault
L
L
No
No
H
H
H
X
X
H
H
H
L
No
Yes
X
Yes
No
H
H
H
H
H
H
H
H
H
Forced Shutdown by
External µP
CTL
No
Deep Discharge
L
L
L
L
Yes
X
No
No
L
L
H
L
H
L
(V
CC
< 4.5V)
Normal Operation
X: Don’t care.
The power dissipation in the MOSFETs is given by:
2
V
×N
S
CELL
I
=
PS
N
S
P = I R
R
+R
+R
+R
×
DSON
DSON_DSO
DSON_CGO
SENSE
CELL
N
P
The MOSFET should be chosen to withstand power dis-
sipation during normal operation and all current fault
conditions. Additional MOSFETs can be added in paral-
lel to help these requirements. Table 3 lists some suit-
able MOSFETs in a small SO-8 package.
where N is the number of cells in series, N is number
S
P
of cells in parallel, and V
is the cell voltage.
CELL
Dissipation during pack-short current fault condition is
given by:
2
P
= (I
)
× R
SENSE
PS
PS
Decoupling Considerations
The MAX1894/MAX1924 must have a reliable V
bias
CC
The R
chosen should be able to withstand P
PS
SENSE
to function properly. A severe overload, such as a short
circuit at the pack terminals, can collapse the battery-
dissipation. Verify power dissipation in normal operation
and other current fault conditions as well.
pack voltage below the V
undervoltage lockout
CC
threshold. The use of a diode-capacitor peak detector
on the V input ensures continued operation during
voltage transients on the battery (Figure 1). Since the
MAX1894/MAX1924 typically consume only 30µA, D1
and C6 can be small, low-cost components. A 30V
Schottky diode with a few mA current capability and a
0.1µF capacitor are sufficient.
Choosing External MOSFETs
The external P-channel MOSFETs act as switches to
enable or disable charging and discharging of batteries.
Different P-channel MOSFETs may be selected depend-
ing on the charge and discharge currents anticipated.
In most applications, the requirements for fast-charge
and discharge MOSFETs are similar and the same type
of MOSFETs can be used. The trickle-charge MOSFET
can be a small-signal type to minimize cost.
CC
The MAX1894/MAX1924 continuously monitor the differ-
ential voltage between the B4P and SRC inputs to
detect the application of a charger. RC filters with simi-
lar time constants must be added to both inputs to
ensure the differential voltage is not corrupted by noise.
The MAX1894/MAX1924 MOSFET drivers have a V
clamp of -14V typical and MOSFETs with maximum V
of -20V can be used. MOSFETs must have a V
greater than the maximum pack voltage.
GS
GS
DS
12 ______________________________________________________________________________________
Advanced Li+ Battery-Pack Protectors
Table 3. MOSFET Selection
P-CHANNEL
MOSFETS
MAXIMUM DRAIN
CURRENT (A)
NORMAL OPERATION
IRF7404
IRF7406
6.7
5.8
Si4431
5.8
NO
V
> V
PS_TH
RSENSE
FOR 450µs
Si4947 (dual)
3.5 EA
Protecting and Filtering Cell Inputs
YES
Resistors in series with each B_P pin are recommend-
ed to limit the current in case there is a short between
adjacent B_P pins (see Figure 1).
SET OD = 1
DSO, CGO, TKO = H
The intermediate cell input bias current is typically
0.5nA. A 1kΩ resistor in series with any intermediate
cell moves the overvoltage trip point by typically 0.5mV,
which is insignificant compared to the 25mV tolerance
in the overvoltage threshold. The top cell input bias cur-
rent during sampling period is typically 60µA. To
reduce the voltage change on the top cell input due to
sampling current, a filter resistance of 10Ω to 50Ω
should be added in series with the top cell. To attain
the desired filter characteristics, the capacitance
across the two top cell input pins should be 1µF.
NO
YES
V
> V + 0.1V
B4P
SRC
Figure 7. Pack-Short Current Fault
Layout Considerations
Good layout is important to minimize the effects of
noise on the system and to ensure accurate voltage
and current measurements. Use the appropriate trace
widths for the high-current paths and keep traces short
to minimize parasitic inductance and capacitance.
Minimize current-sense resistor trace lengths and make
use of Kelvin connections to the resistor. Provide ade-
quate space and board area for the external MOSFETs
and sense resistor to dissipate the heat required. Place
RC filters close to B1P–B4P pins.
The MAX1894/MAX1924 have internal ESD diodes on
each B_P pin for ESD protection up to 2kV. When high-
er ESD ratings are needed, capacitors (typically 0.1µF)
can be added across adjacent B_P pins (see Figure 1).
The RC filters improve the device immunity to ESD and
filter the noise spikes on B1P–B4P to prevent the
MAX1894/MAX1924 from being triggered and latched
prematurely by noise spikes.
Control Pins SHDN and CTL
SHDN and CTL allow external logic or microprocessors
to control the MAX1894/MAX1924 gate drivers. Drive
CTL high to turn off the three protection MOSFETs: DSO,
CGO, and TKO. Drive SHDN high to force the MAX1894/
MAX1924 into shutdown mode (with no charger applied).
SHDN and CTL do not affect the state machine. Toggling
these two pins does not change the state or reset any
fault conditions. If external control circuitry or a micro-
processor is not used, connect SHDN and CTL to PKN.
Chip Information
TRANSISTOR COUNT: 4259
______________________________________________________________________________________ 13
Advanced Li+ Battery-Pack Protectors
SHDN
CTL
B4P
B3P
SRC
HV
CELL
SELECTOR
CLOCK
RDY
DSO
DRIVER
B2P
B1P
BN
OV FAULT
UV FAULT
STATE
MACHINE
SRC
CMP
OVER AND
UNDER
THRESHOLDS
FAULT
LOGIC
CGO
TKO
HV
DRIVER
REF
HYSTERESIS
BN
SRC
CMP
+145mV
HV
DRIVER
CHARGE CURRENT
FAULT
PKN
DISCHARGE-CURRENT
FAULT
BN
CMP
-100mV
SET/RESET
TIMER
PACK-SHORT
CURRENT FAULT
MAX1894
MAX1924
CMP
+405mV
BN
V
CC
ON
DSCHG
CHG
CMP
S
Q
-50mV
LATCH
3.5V REG
BIAS
R
B4P
CMP
+50mV
RDY
SRC
UV FAULT
SHDN
Figure 8. Simplified Functional Diagram
14 ______________________________________________________________________________________
Advanced Li+ Battery-Pack Protectors
OVERDISCHARGE
PROTECTION
R5
10Ω
PACK +
C5
2.2µF
16
SRC
15
14
13
DSO
CGO
TKO
BN
OVERCHARGE
PROTECTION
D1
CMPSH-3
2
1
V
CC
B4P
R4
C6
51Ω
0.1µF
C4
1µF
R3
1kΩ
MAX1894X
MAX1924X
3
4
B3P
IC3
B2P
IC2
B1P
IC1
BN
C3
0.1µF
R2
1kΩ
5
C2
0.1µF
R1
12
11
6
7
SHDN
CTL
MICRO-
CONTROLLER
1kΩ
8
9
C1
0.1µF
PKN
10
R
SENSE
0.02Ω
PACK -
Figure 9. Typical Applications Circuit without Trickle Charge
______________________________________________________________________________________ 15
Advanced Li+ Battery-Pack Protectors
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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