MAX1874ETE+T [MAXIM]
Power Supply Support Circuit, Fixed, 1 Channel, BICMOS, 5 X 5 MM, 0.80 MM HEIGHT, MO-220-WHHB, TQFN-16;
| 型号： | MAX1874ETE+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Power Supply Support Circuit, Fixed, 1 Channel, BICMOS, 5 X 5 MM, 0.80 MM HEIGHT, MO-220-WHHB, TQFN-16 信息通信管理 |
| 文件： | 总17页 (文件大小：899K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2912; Rev 1; 2/07
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
General Description
Features
The MAX1874 charges a single-cell Li+ battery from
both USB and AC adapter sources. It also includes bat-
tery-to-input power switchover, so the system can be
powered directly from the power source rather than
from the battery.
♦ Charge from USB or AC Adapter
♦ Automatic Switchover to AC Adapter
♦ Thermal Limiting Simplifies Board Design
♦ Small, High-Power 16-Pin Thin QFN Package
♦ Input Protection Up to 18V
In its simplest application, the MAX1874 needs no
external MOSFET or diodes, and accepts input volt-
ages up to 6.5V; however, DC input overvoltage protec-
tion up to 18V can be added with a single SOT PFET.
♦ Soft-Start
♦ Automatic Battery-to-Input Load Switch
On-chip thermal limiting simplifies printed circuit board
(PCB) layout and allows optimum charging rate without
the thermal limits imposed by worst-case battery and
input voltage. When the MAX1874 thermal limit is
reached, the charger does not shut down but simply
reduces charging current.
Ordering Information
PIN-
PACKAGE
PKG
CODE
PART
TEMP RANGE
Ambient or battery temperature can be monitored with
an external thermistor. When the temperature is out of
range, charging pauses.
16 Thin QFN
5mm x 5mm
MAX1874ETE
-40°C to +85°C
T1655-2
Other features include a CHG output to indicate when
battery current tapers below a predetermined level. DC
power-OK (DCOK), USB power-OK (UOK), and power-
on (PON) outputs indicate when valid power is present.
These outputs drive logic or power-selection MOSFETs
to disconnect the charging sources from the load and
to protect the MAX1874 from overvoltage.
Typical Operating Circuit
DC INPUT
DC
PON
MAX1874
The MAX1874 contains no logic for communication with
the USB host. It must receive instructions from a local
microcontroller. The MAX1874 is available in a 16-pin
5mm ✕ 5mm thin QFN package and operates over the
-40°C to +85°C temperature range.
DCOK
DCLV
BATT
Li+
CELL
UOK
USB
Applications
CHG
USEL
EN
USB INPUT
TO REF
PDAs
Cell Phones
500mA
100mA
Wireless Appliances Digital Cameras
DCI
Pin Configuration
REGULATOR
REF
TOP VIEW
16 15 14 13
THRM
GND
DCLV
1
2
3
4
12 USB
11 BYP
10 PGND
DC
CHG
NTC
THERMISTOR
MAX1874
BYP
PGND
USEL
9
REF
5
6
7
8
THIN QFN
5mm x 5mm
Functional Diagram appears at the end of the 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.
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
ABSOLUTE MAXIMUM RATINGS
DC, DCOK to GND.................................................-0.3V to +20V
Continuous Power Dissipation (T = +70°C)
A
16-Pin 5mm ✕ 5mm Thin QFN
DCLV, BYP, USB, UOK, DCI, REF, USEL, THRM,
(derate 21.3mW/°C above +70°C)...................................1.7W
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Maximum Junction Temperature .....................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
EN, BATT, CHG, PON to GND .............................-0.3V to +7V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Current (DCLV) ..................................................1.1A
Continuous Current (USB) ....................................................0.6A
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
= V
= V = V
= 5V, V
= 4.2V, V
= V
/ 2, Circuit of Figure 2, T = 0°C to +85°C, unless otherwise
REF A
USB
DC
DCLV
EN
USEL
BATT
THRM
noted. Typical values are at T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
INPUT VOLTAGE RANGES AND INPUT CURRENT
Maximum DC Input Voltage with
Overvoltage Protection
Q2 input MOSFET must be in place; charging
occurs only below 6.2V, Figures 3, 4, and 5
18
V
Maximum DC Input Voltage Without
Overvoltage Protection
DC = DCLV, Q2 input MOSFET not on circuit,
Figure 2
6.5
V
V
Maximum Input Voltage for Charging
6.0
6.2
2
6.5
4
V
V
= 0V
= 5V
EN
EN
DC Supply Current
mA
4
6
DCLV Operating Voltage Range
DCLV Shutdown Supply Current
USB Input Voltage Range
4.35
4.35
6.00
500
6.50
750
3
V
µA
V
V
= 0V
= 0V
300
EN
V
V
V
500
2
µA
mA
µA
nA
Ω
EN
EN
EN
USB Supply Current
= 5V, V = 0V
DC
= 5V, V = 5V
160
1
300
100
DC
DCI Input Current
BYP Output Resistance
THRM Input Bias Current
BATTERY VOLTAGE
(Note 1)
5
1
100
nA
BATT Regulation Voltage
BATT Prequal Voltage Threshold
Prequal Threshold Hysteresis
4.1685
2.8
4.20
3
4.2315
3.2
V
V
BATT rising
70
mV
I
I
I
= 100mA
= 500mA
100
200
250
USB
USB
DCIN
USB Charging Headroom
DC Charging Headroom
mV
mV
V
= 800mA
I
= 0 to 500µA, 4V < V
or V
< 6.5V;
USB
REF
DC
REF Voltage (Buffered Output)
2.94
3
3.06
does not affect BATT regulation accuracy
2
_______________________________________________________________________________________
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
= V
= V = V
= 5V, V
= 4.2V, V
= V
/ 2, Circuit of Figure 2, T = 0°C to +85°C, unless otherwise
REF A
USB
DC
DCLV
EN
USEL
BATT
THRM
noted. Typical values are at T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
BATTERY CHARGING AND PRECHARGE CURRENT
DCI Voltage Range
0.1 x V
950
V
V
REF
REF
V
V
= V
= V
1000
520
455
82
7
1050
550
495
95
DCI
DCI
REF
REF
DCI Voltage to BATT Current
USB Charging Current
mA
/ 2
490
USEL = high
USEL = low
mA
Soft-Start Current-Ramp Time
Prequal Charging Current
BATT Input Current
Measured from 10% to 90%
= 2.5V
ms
mA
µA
µA
V
35
55
5
70
7.5
2
BATT
No DC or USB power, V
= 4.2V
BATT
BATT Shutdown Current
EN = GND, USB- and/or DC-powered
1
THERMISTOR MONITOR AND DIE-TEMPERATURE REGULATION
THRM COLD Trip Level
THRM HOT Trip Level
THRM Disable Threshold
Internal Die Thermal Limit
(Note 2)
(Note 2)
0.72
0.28
50
0.74
0.29
100
0.76
0.30
150
V
V
REF
REF
mV
+105
°C
LOGIC INPUT/OUTPUTS AND GATE DRIVERS
PON pulled up to active input (DCLV or USB),
or V = 5V
PON High Output Resistance
25
Ω
V
DCLV
USB
PON Low Output Resistance
DCOK Low Output Resistance
DCOK Off-Leakage Current
UOK Output Resistance
PON resistance to GND, V
= V
= 0
USB
120
25
kΩ
Ω
DCLV
DCOK pulled low
V
= 12V, V
= 0V
DC
1
µA
Ω
DCOK
UOK resistance to GND, V
= 0
25
DC
UOK Off-Leakage Current
V
= 6.5V
1
µA
UOK
DC input (% of charge current set at DCI)
8
12.5
25
19
30
USB input, USEL = 5V (% of USB charging current)
20
CHG Threshold to Indicate Battery Full,
Battery Current Falling (Note 3)
%
Voltage
mode
USB input with USEL = 0
Sinking 10mA sink
CHG Logic-Low Output
0.4
1
V
µA
V
CHG Leakage Current
V
= 6.5V
CHG
EN, USEL Logic-Input High Level
EN, USEL Logic-Input Low Level
EN, USEL Input Bias Current
1.6
0.4
1
V
µA
_______________________________________________________________________________________
3
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
= V
= V = V
= 5V, V
= 4.2V, V
= V
/ 2, Circuit of Figure 2, T = 0°C to +85°C, unless otherwise
REF A
USB
DC
DCLV
EN
USEL
BATT
THRM
noted. Typical values are at T = +25°C.)
A
PARAMETER
TIMING
CONDITIONS
MIN
TYP
MAX
UNITS
DC Rising to DCOK Falling
USB Rising to UOK Falling
USB = open, DC rising to 5V
DC = open, USB rising to 5V
20
20
ms
ms
DC Falling to DCOK Going
Open-Drain Propagation Delay
USB = open, 1kΩ pullup
DC = open, 10kΩ pullup
2
2
µs
µs
USB Falling to UOK Going
Open-Drain Propagation Delay
USB = open, DC step to 5V, BATT = 3.6V,
100kΩ pulldown
DC Rising to PON Rising (90%)
USB Rising to PON Rising (90%)
20
20
2
ms
ms
µs
DC = open, V
step to 5V, V
= 3.6V,
BATT
USB
100kΩ pulldown
DC Falling to PON Going
Open-Drain Propagation Delay
USB = open, 100kΩ pulldown
DC = open, 100kΩ pulldown
USB Falling to PON Going
Open-Drain Propagation Delay
2
µs
ELECTRICAL CHARACTERISTICS
(V
= V = V
= V = V
= 5V, V
= 4.2V, V
= V / 2, Circuit of Figure 2, T = -40°C to +85°C, unless otherwise
REF A
USB
DC
DCLV
EN
USEL
BATT
THRM
noted. Typical values are at T = +25°C.) (Note 4)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
INPUT VOLTAGE RANGES AND INPUT CURRENT
Maximum DC Input Voltage with
Overvoltage Protection
Q2 input MOSFET must be in place; charging
occurs only below 6.2V, Figures 3, 4, and 5
18
V
Maximum DC Input Voltage Without
Overvoltage Protection
DC = DCLV, Q2 input MOSFET not on circuit,
Figure 3
6.5
V
V
Maximum Input Voltage for Charging
6.0
6.5
4
V
V
= 0V
= 5V
EN
EN
DC Supply Current
mA
6
DCLV Operating Voltage Range
DCLV Shutdown Supply Current
USB Input Voltage Range
4.35
4.35
6.00
500
6.50
750
3
V
V
= 0V
= 0V
µA
V
EN
V
V
V
µA
mA
µA
nA
nA
EN
EN
EN
USB Supply Current
= 5V, V = 0V
DC
= 5V, V = 5V
300
100
100
DC
DCI Input Current
THRM Input Bias Current
4
_______________________________________________________________________________________
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
ELECTRICAL CHARACTERISTICS (continued)
(V
= V = V
= V = V
= 5V, V
= 4.2V, V
= V
/ 2, Circuit of Figure 2, T = -40°C to +85°C, unless otherwise
USB
DC
DCLV
EN
USEL
BATT
THRM
REF A
noted. Typical values are at T = +25°C.) (Note 4)
A
PARAMETER
BATTERY VOLTAGE
CONDITIONS
MIN
TYP
MAX
UNITS
4.1685
2.8
BATT Regulation Voltage
4.2315
3.2
V
V
BATT Prequal Voltage Threshold
BATT rising
= 0 to 500µA, 4V < V
I
or V
< 6.5V;
USB
REF
DC
REF Voltage (Buffered Output)
2.94
3.06
V
does not affect BATT regulation accuracy
BATTERY CHARGING AND PRECHARGE CURRENT
DCI Voltage Range
0.1 x V
930
V
V
REF
REF
V
V
= V
= V
1070
565
495
95
DCI
DCI
REF
REF
DCI Voltage to BATT Current
USB Charging Current
mA
/ 2
490
USEL = high
USEL = low
mA
Prequal Charging Current
BATT Input Current
V
= 2.5V
40
70
mA
µA
µA
BATT
No DC or USB power, V
= 4.2V
7.5
2
BATT
BATT Shutdown Current
EN = GND, USB and/or DC powered
THERMISTOR MONITOR AND DIE-TEMPERATURE REGULATION
THRM COLD Trip Level
THRM HOT Trip Level
THRM Disable Threshold
(Note 2)
(Note 2)
0.72
0.28
50
0.76
0.30
150
V
V
REF
REF
mV
LOGIC INPUT/OUTPUTS AND GATE DRIVERS
DCOK Off-Leakage Current
UOK Off-Leakage Current
V
V
= 12V, V
= 0V
DC
1
1
µA
µA
DCOK
= 6.5V
UOK
DC input (% of charge current set at DCI)
8
20
CHG Threshold to Indicate Battery Full,
Battery Current Falling (Note 3)
%
USB input, USEL = 5V
(% of USB charging current)
20
30
CHG Logic-Low Output
Sinking 10mA sink
0.4
1
V
µA
V
CHG Leakage Current
V
= 6.5V
CHG
EN, USEL Logic-Input High Level
EN, USEL Logic-Input Low Level
EN, USEL Input Bias Current
1.6
0.4
1
V
µA
Note 1: BYP internally connects to the active power input (DCLV or USB). DCLV takes priority if both inputs are powered.
Note 2: These limits guarantee +5°C accuracy with 5% accuracy of thermistor beta (3450 nominal) with 2°C of hysteresis.
Note 3: The CHG output does not go high unless charge current is below the indicated threshold (as set by DCI) and the charger is in
voltage-mode operation. In 100mA USB mode, CHG goes high when the charger transitions from current to voltage mode.
Note 4: Specifications to -40°C are guaranteed by design, not production tested.
_______________________________________________________________________________________
5
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
Typical Operating Characteristics
(V
= V
= V
= V
= 5V, V
= 4.2V, V
= V
/ 2, V
= V
, V
REF USEL
= 5V, Circuit of Figure 4, T = +25°C,
USB
DC
DCLV
EN
BATT
THRM
REF
DCI
A
unless otherwise noted.)
USB INPUT CURRENT
vs. USB INPUT VOLTAGE
DC INPUT CURRENT
vs. DC INPUT VOLTAGE
USB INPUT CURRENT
vs. USB INPUT VOLTAGE (V = 0)
EN
5.0
V
= 5V, V FLOATING
DC
INCLUDES R3 AND R4 CURRENTS
V
V
V
= 0
BATT
= 5V
EN
V
= 0
EN
14
12
10
8
USB
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
= 4.2V
INCLUDES R3 AND R4 CURRENTS
EN
INCLUDES R2 CURRENT
6
4
2
0
0
2
4
6
8
10 12 14 16 18 20
(V)
0
0
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
V
V
(V)
DC
USB
V
(V)
USB
CHARGE CURRENT vs. BATTERY VOLTAGE
(I vs. V
CHARGE CURRENT
vs. DC INPUT-VOLTAGE HEADROOM
CHARGE CURRENT
vs. USB VOLTAGE HEADROOM
)
BATT
BATT
1000
900
800
700
600
500
400
300
200
100
0
800
700
600
500
400
300
200
100
0
600
500
400
300
200
100
0
V
V
= 5
= 0
EN
USB
I
= SET TO 750mA
BATT
DCI SET FOR I
= 750mA
BATT
V
= V
= 5V
DC
DCLV
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
(V)
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
(V - V ) (V)
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
(V - V ) (V)
V
BATT
DC BATT
USB
BATT
BATTERY TERMINATION VOLTAGE
vs. TEMPERATURE
CHARGE CURRENT vs. TEMPERATURE
WITH THERMAL REGULATION
CHARGE CURRENT vs. V
DCI
4.25
4.24
4.23
4.22
4.21
4.20
4.19
4.18
4.17
4.16
4.15
1.2
1.0
0.8
0.6
0.4
0.2
0
1.2
1.0
0.8
V
V
V
= V
REF
= 5V
= 3.9V
DCI
DC
BATT
0.6
0.4
0.2
0
-40 -25 -10
5
20 35 50 65 80
0.5
1.0
1.5
(V)
2.0
2.5
3.0
-40 -25 -10
5
20 35 50 65 80 95 110 125
TEMPERATURE (°C)
V
TEMPERATURE (°C)
DCI
6
_______________________________________________________________________________________
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
Typical Operating Characteristics (continued)
(V
= V
= V
= V
= 5V, V
= 4.2V, V
= V
/ 2, V
= V
, V
REF USEL
= 5V, Circuit of Figure 4, T = +25°C,
USB
DC
DCLV
EN
BATT
THRM
REF
DCI
A
unless otherwise noted.)
OFF-BATTERY LEAKAGE
vs. DC INPUT VOLTAGE
OFF-BATTERY LEAKAGE
vs. USB INPUT VOLTAGE
USB LEAKAGE vs. DC INPUT VOLTAGE
10
9
10
9
8
7
6
5
4
3
2
1
0
600
V
V
V
V
= 0
USB
BATT
EN
LEAKAGE FROM USB TO GND
V
V
V
= 0
EN
DCLV
BATT
= 0
V
= 5V
= V = 0
EN
DC
500
400
300
200
100
0
= 4.2V
DCLV
8
= 4.2V
= V
DC
7
6
5
4
3
2
1
0
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
2
4
6
8
10 12 14 16 18
(V)
V
DCIN
(V)
V
(V)
V
USB
DCIN
DC CONNECT WAVEFORMS
= 0, V = 3.9V
BATTERY CURRENT AND VOLTAGE
vs. TIME
RESPONSE TO OVERVOLTAGE INPUT
V
USB
USB = 0
BATT
MAX1874 toc15
MAX1874 toc14
MAX1874 toc13
1000
900
800
700
600
500
400
300
200
100
0
8.0
7.2
6.4
5.6
4.8
4.0
3.2
2.4
1.6
0.8
0
1.5AHr CELL
DC
10V/div
I
BATT
20V/div
DC
CHG
DCLV
PON
10V/div
10V/div
DCLV
PON
5V/div
5V/div
V
BATT
100
1A/div
I
BATT
DCOK
20V/div
DCOK
10V/div
40ms/div
0
50
150
200
250
300
40ms/div
TIME (MIN)
DC STARTUP WAVEFORMS FOR ENABLE
= 3.9V
DC CONNECT WAVEFORMS
= 5V, V = 3.9V
USB CONNECT WAVEFORMS
V
BATT
V
V
DC
= 0, V
= 3.9V
USB
BATT
BATT
MAX1874 toc16
MAX1874 toc18
MAX1874 toc17
DC
10V/div
5V/div
5V/div
EN
5V/div
5V/div
USB
PON
DCLV
PON
10V/div
10V/div
CHG
1A/div
500mA/div
5V/div
I
I
BATT
BATT
I
500mA/div
BATT
DCOK
10V/div
UOK
40ms/div
10ms/div
40ms/div
_______________________________________________________________________________________
7
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
Pin Description
PIN
1
NAME
DCLV
DC
FUNCTION
Low-Voltage Charger Input. DCLV charges BATT through an internal MOSFET. Maximum operating
voltage at this pin is 6.0V. When an overvoltage protection MOSFET is connected, DCLV is connected to
DC when the input voltage is suitable for charging.
2
Voltage-Sense Pin for DC Input from AC Adapter. Maximum operating voltage at this pin is 18V.
CHG is an active-low, open-drain output that goes low when the MAX1874 is charging and goes high
when both of the following conditions are met (see the Battery Full (CHG) section):
1) Charge current drops to a set threshold (Table 2).
3
4
CHG
2) The charger is in voltage mode.
USEL is a logic input that sets USB source charging current to 500mA when USEL is logic high and to
100mA when USEL is logic low.
USEL
Enable/Disable Input. Drive EN high to enable the device. When EN is low, UOK, DCOK, PON, and REF
remain active.
5
6
7
EN
GND
DCI
Ground
The voltage at this input sets the fast-charge current when the DCLV input is powering the charger. See
the Charging Current section.
THRM pauses charging when an externally connected thermistor (10kΩ at +25°C) is at less than 0°C or
greater than +50°C. Connect to GND to disable. See the External Thermistor Monitor (THRM) section.
8
THRM
3V Reference Output. Sources up to 500µA to bias I
GND. REF loading does not affect BATT regulation accuracy.
and external thermistor. Bypass with 0.1µF to
DCI
9
REF
PGND
BYP
10
11
12
13
Power Ground. Connect to GND at a single, low-impedance point.
BYP powers internal circuitry and switches to the active input (either DCLV or USB). Bypass with a 2.2µF
capacitor to GND.
USB
USB Charger Input. Charges BATT through an internal MOSFET.
UOK is an active-low, open-drain output that goes low to indicate when the USB input is the valid
charging source.
UOK
PON is an active-high, open-drain output with an internal 120kΩ resistor to ground that goes high when
V
or V
> V
. PON can directly drive an external PFET that disconnects the battery from the
BATT
14
PON
DC
USB
system load when power is applied.
15
16
BATT
Charge Output. Connect to the positive terminal of the Li+ battery.
DCOK
DCOK is an active-low, open-drain output that goes low when 3.5V < V
< 6.2V.
DC
8
_______________________________________________________________________________________
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
Functional Diagram
BYP
5Ω
DC
OVERVOLTAGE AND
UNDERVOLTAGE
DETECT
5Ω
INPUT POWER-
OK SELECT
DCOK
PON
N
120kΩ
DCLV
USB
BATT
0.25Ω
0.4Ω
MAX1874
USB/DCLV
DETECT
CHG
V
I
BATT
USB_SENSE
I
DCLV_SENSE
UOK
LINEAR
REGULATOR
N
N
TEMPERATURE
DCI
USEL
3.00V
REFERENCE
REF
THERMISTOR
COMPARATORS
GND
_______________________________________________________________________________________
9
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
100mA through the USEL input. When power is taken
Detailed Description
from the DC input, charge current is linearly set by the
The MAX1874 charges a single-cell Li+ battery from
voltage at DCI. The MAX1874 charge current can also
either USB power sources or AC adapter sources. It
be DAC controlled with the output of a DAC connected
contains a complete two-input linear charger that controls
to DCI. See the Charging Current section.
both battery charge current and voltage. In addition to
all charging functions, the MAX1874 includes voltage-
sensing and switchover circuitry that selects the active
input source. When both inputs are active, priority is
given to the AC adapter (DC). Charging current is regu-
lated with on-chip power MOSFETs, so no external
MOSFETs are required for a basic two-input charger.
Additional features such as input-voltage protection and
battery-load switching can be added with external
MOSFETs that are driven directly from MAX1874 outputs.
Enable (EN)
The enable input, EN, switches the MAX1874 on or off.
With EN high, the MAX1874 is on and can begin charg-
ing. When EN is low, UOK, DCOK, PON, and REF remain
active. Charging stops when EN is low, but the chip
remains biased and continues to draw current from the
input supplies so power-monitoring outputs can remain
valid.
USB-to-Adapter Power Handoff
The MAX1874 can charge from either the USB input or
the DC input. It cannot charge from both sources at the
same time. The IC automatically selects the active input
and charges from that. If both power sources are
active, the adapter input (DC) takes precedence. Table
1 describes the switchover between DC and USB.
The MAX1874 also features a thermal regulation loop
that adjusts charging current so the die temperature
remains below +105°C. See the Package Thermal
Limiting section. This on-chip thermal control simplifies
PCB layout and allows the optimum charging rate to be
set without the thermal limits imposed by worst-case
battery and input voltage. When the MAX1874 thermal
limit is reached, the charger does not shut down but
reduces charging current.
DC serves as the sense input for the adapter power
source. This input senses when DC is above 6.2V (maxi-
mum range is 18V) or below 4V. When it senses the DC
source is above 6.2V, DCOK goes high, indicating an
invalid DC input. See the DC Power-OK (DCOK) section.
In addition to, and separate from, its internal die tem-
perature control, the MAX1874 can also monitor ambi-
ent or cell temperature with an external thermistor
connected to THRM. When the thermistor temperature
is out of range (greater than +50°C or less than 0°C),
charging stops until the temperature returns to normal.
See the External Thermistor Monitor (THRM) section.
When power is connected to DC, the MAX1874 requires
20ms to validate the input. Consequently, charging is
interrupted for 20ms until it is determined that input
power is good. Also, when DC power is removed while
valid USB power is present, charging is interrupted for
20ms before transferring to the USB source.
Other features include a CHG output to indicate battery
full (when charge current tapers to a percentage of
fast-charge current). DCOK, UOK, and power-on (PON)
outputs indicate when valid power is present. These
outputs can drive overvoltage protection and power
selection MOSFETs (Figures 3, 4, and 5).
DC Power-OK (DCOK)
DCOK is an active-low, open-drain output that goes low
when V
is below 6.2V or above 3.5V. DCOK can be
DC
used as a logic output, but is also designed to drive an
external MOSFET (Q2 in Figures 3, 4, and 5). This allows
the charger to protect the input from overvoltage up to
18V. Charging is disabled for inputs over 6.2V. An exter-
nal 1kΩ pullup resistor keeps DCOK high (external
MOSFET off) until it is certain the voltage is within the
When charging is stopped or input power is removed,
battery leakage is typically 5µA. No input blocking
diodes are required to prevent battery drain.
With USB power connected, but without power at the
DC input, charge current can be set to either 500mA or
Table 1. USB and DC Input Selection
4V < V
< 6.2V AND
4V < V
< 6.5V AND
V
< 4V OR V
>
DC
< 4V
DC
USB
DC
V
DC
> 18V OR V
> 6.5V
USB
0 < V
< 6.5V
V
DC
< 4V OR V
> 6.2V
6.2V, AND V
USB
DC
USB
Exceeds operating input
range. Not allowed. See the
Absolute Maximum Ratings
section.
1)
2)
USB powers device and supplies charging
current.
DCLV disconnected from DC source through
external MOSFET (Q2 Figures 3, 4, and 5).
DCLV powers device
and supplies charging
current.
No charging
Note: V takes precedence when both inputs are valid.
DC
10 ______________________________________________________________________________________
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
acceptable range. To verify that the input voltage is
stable, DCOK has an internal delay of 20ms before con-
necting power to DCLV. DCOK remains operational
when EN is low (charger off).
100mA. A logic low on USEL selects a 100mA maximum
charging current. A logic high on USEL selects a 500mA
maximum charging current.
DCI
When charging from the DCLV input, the voltage at DCI
sets the charge current. The voltage-to-current transfer
USB Power-OK (UOK)
UOK is an active-low, open-drain output that goes low
to indicate that V
is valid (greater than 4V). UOK
ratio from DCI to BATT is 1A/V . The DCI pin should
REF
USB
remains operational when EN is low (charger off). An
external 10kΩ pullup resistor keeps UOK high until it is
certain that power is within the acceptable range. UOK
can be used as a logic output, or to control a MOSFET
that switches USB power directly to the system load
when the MAX1874 is powered from a USB source (Q1
in Figure 4).
be connected to a resistive divider from REF to DCI to
GND (R5 and R6 in Figures 2 and 4). In this configura-
tion, I
is as follows:
BATT
I
= [R6 / (R5 + R6)] Amps
BATT
R5 and R6 should total 25kΩ or more to minimize loading
on REF. Connecting DCI directly to REF results in a 1A
charge current.
Bypass (BYP)
BYP is the bypass connection for the MAX1874’s inter-
nal power rail. Bypass to GND with a 2.2µF or greater
capacitor. The voltage at BYP is supplied from either
DCLV or USB through an internal 5Ω switch network.
Battery Full (CHG)
CHG is low when the MAX1874 is charging in either the
prequal or full-charging state. CHG then goes high
when the charging current falls below a percentage of
the set fast-charge current (Table 2) and the charger is
in voltage mode (V
near 4.2V). The CHG current
Power On (PON)
BATT
threshold is a function of the charger mode. When
charging from a DC source, CHG goes high when
PON goes high when V
or V
is within its normal
DC
USB
operating range. PON can be used as a logic output to
indicate power is connected or can drive an external
P-channel MOSFET that switches the system load from
the battery to an external source when power is applied.
See Q3 in Figures 4 and 5.
I
falls to 12.5% of the current set by V
and the
DCI
BATT
charger is in voltage mode (V
near 4.2V). When
BATT
charging from a USB source with USEL high, CHG
goes high when I falls to 125mA and the charger is
BATT
in voltage mode. If the MAX1874 is charging from a
USB source with USEL low, CHG goes high when the
charger enters voltage mode.
Charging Current
Precharge Current
When the MAX1874 is powered with a battery connect-
ed, the IC first detects if the cell voltage is ready for full
charge current. If the cell voltage is less than the pre-
qual level (3V typ), the battery is precharged with a
50mA current until the cell reaches the proper level.
The full charging current, as set by USEL or DCI, is
then applied.
Package Thermal Limiting
On-chip thermal limiting in the MAX1874 simplifies PCB
layout and allows charging rates to be automatically
optimized without constraints imposed by worst-case
minimum battery voltage, maximum input voltage, and
maximum ambient temperature. When the MAX1874
thermal limit is reached, the charger does not shut
down but simply reduces charging current. This allows
the board design to be optimized for compact size and
typical thermal conditions. The MAX1874 reduces
charging current to keep its die temperature below
+105°C.
USEL
The charging current from the USB source is selected
by USEL. A USB source can supply a maximum of
100mA or 500mA. USB hosts and powered hubs typi-
cally supply 500mA, while unpowered hubs supply
Table 2. CHG Battery Full Indication
CHARGING SOURCE
CHARGE CURRENT THRESHOLD FOR CHG GOING HIGH
12.5% of Charge Current Set by DCI and Charger in Voltage Mode
125mA and Charger in Voltage Mode
DCLV Charging
USB Charging 500mA (USEL high)
USB Charging 100mA (USEL low)
Charger in Voltage Mode
Note: CHG does not go high when charge current is reduced by the thermal regulation loop.
______________________________________________________________________________________ 11
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
The MAX1874’s thin QFN package includes a bottom
metal plate that reduces thermal resistance between the
die and the PCB. The external pad should be soldered to
a large ground plane. This helps dissipate power and
keeps the die temperature below the thermal limit. The
REF
MAX1874 thermal resistance from the die to the package
0.1µF
10kΩ
thermal pad is typically 5°C/W. The thermal resistance of
100mV
TO REGULATOR
2
1in of 1oz copper on typical FR4 PC board material in
THRM
free air is +42°C/W (typ). Consequently, the PC board
pad area dominates the MAX1874’s ability to dissipate
heat. The MAX1874’s thermal regulator is set for a
+105°C die temperature. With the example thermal resis-
tance of +47°C/W, the MAX1874 charge-current thermal
limiting can be expected to occur when dissipating
approximately 1.7W at +25°C ambient, and when dissi-
pating approximately 0.75W at +70°C ambient.
T
COLD
THERMISTOR
10KΩ AT +25°C
T
HOT
The power dissipated in the charger is P
= [V
IN
DISS
(either V
or V
) - V
BATT
] ✕ I . Power dis-
USB
DCLV
CHARGE
Figure 1. Thermistor Sensing Block Diagram
sipation drops as the battery voltage rises, so thermal-
charge current limiting, if it occurs, typically releases
soon after charging begins and has little impact on
charge time.
Battery-Load Switch
When input power is connected to the charger, some
systems prefer that the battery is disconnected from the
load and that system load current is taken directly from
the DC input or USB source. This is an alternative to the
basic case where the system load is permanently con-
nected to the battery. The later setup is lower cost but
has the disadvantage that if the battery is completely
discharged, the system might not be ready to operate
immediately, or might have limited functionality immedi-
ately upon plugging in the charger. If the battery has a
load-disconnect switch, the system is more complex,
but operation does not depend on the state of the bat-
tery. When system power is taken from the DC or USB
input source, use D1, D2, Q1, and Q2 (Figure 4).
External Thermistor Monitor (THRM)
The MAX1874 features an internal window comparator to
monitor battery pack temperature or ambient tempera-
ture with an external negative temperature coefficient
thermistor. In typical systems, temperature is monitored
to prevent charging at ambient temperature extremes
(below 0°C or above +50°C). When the temperature
moves outside these limits, charging is stopped. If the
V
returns to within its normal window, charging
THERM
resumes. Connect THRM to GND when not using this
feature. The THRM block diagram is detailed in Figure 1.
Note that the temperature monitor at THRM is entirely
separate from the on-chip temperature limiting dis-
cussed in the Package Thermal Limiting section.
A partial approach to battery-load switching can con-
nect the AC power adapter (DC) directly to the load, but
not USB power (Figure 5). This can be useful when USB
power is insufficient to fully power the system and
charge the battery. When DC is powered, D2 provides a
direct connection to the system and Q3 disconnects the
battery. The battery does not power the load while it is
charging. When only USB is connected, there is no
bypass path from USB to the system. The battery is
charged from the BATT output, and any system power is
drawn from the battery through D5. If the system load
exceeds the current supplied by the charger from USB
(500mA or 100mA), then the battery can still discharge.
In addition, if the system load does not allow the BATT
current to fall below the USB battery full current thresh-
old listed in Table 2, then CHG does not go high to indi-
cate a full battery.
The input thresholds for the THRM input are 0.74 ✕
V
for the COLD trip point and 0.29 ✕ V
for the
REF
REF
HOT trip point.
Applications Information
Input Overvoltage Protection Switch
The DCLV input from an AC adapter or other source
can be protected against overvoltage of up to 18V by
connecting an external P-channel MOSFET (Q2 in
Figures 3, 4, and 5) between DC and DCLV. When V
DC
exceeds 6.2V, the DCOK output turns the P-channel
MOSFET off. On power-up, DCOK remains high until it
has been verified that V
is in range. If protection
DC
above 6.5V is not needed, then the MOSFET from the
DC to DCLV can be omitted (Figure 2).
12 ______________________________________________________________________________________
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
DC INPUT
UP TO 6.0V
DC
C5
4.7µF
10V CERAMIC
MAX1874
DCOK
DCLV
UOK
PON
BATT
C3
2.2µF
6.3V CERAMIC
Li+
CELL
250mΩ
USB
DCI
CHG
USEL
EN
USB INPUT
C1
4.7µF
500mA
100mA
400mΩ
6.3V CERAMIC
R5
100kΩ
REGULATOR
TO REF
REF
C6
0.1µF
R4
10kΩ
R6
301kΩ
10V CERAMIC
THRM
GND
NTC
THERMISTOR
10kΩ AT +25°C
BYP
PGND
C4
2.2µF
10V CERAMIC
Figure 2. A Minimal Circuit that Assumes System Load Is Only Connected to the Battery. The circuit has a 6.5V maximum input and
disables charging for inputs over 6.2V.
R2
0VP UP TO 18V
CHARGING UP TO 6.0V
1kΩ
5%
DC
C5
4.7µF
25V CERAMIC
Q2
FDN302
0.055Ω, -20V
MAX1874
DCOK
PON
BATT
DCLV
UOK
C2
C3
1µF
2.2µF
Li+
CELL
250mΩ
10V CERAMIC
6.3V CERAMIC
USB
CHG
USEL
EN
USB INPUT
C1
4.7µF
500mA
100mA
6.3V CERAMIC
400mΩ
REGULATOR
TO REF
REF
DCI
C6
0.1µF
R4
10kΩ
10V CERAMIC
THRM
GND
NTC
THERMISTOR
10kΩ AT +25°C
BYP
PGND
C4
2.2µF
10V CERAMIC
Figure 3. A circuit with overvoltage protection MOSFET (Q2) on DC input withstands up to 18V from the AC adapter and disables
charging at inputs over 6.2V.
______________________________________________________________________________________ 13
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
D2
500mA,
SCHOTTKY
(MBR0520L)
OVP UP TO 18V
R2
1kΩ
CHARGING UP TO 6.0V
TO SYSTEM
LOAD
DC
D1
500mA,
SCHOTTKY
(MBR0520L)
Q2
FDN302
0.055Ω, -20V
C5
4.7µF
25V CERAMIC
Q3
FDN302
0.055Ω, -20V
MAX1874
DCOK
PON
BATT
DCLV
UOK
Q1
FDN302
C3
2.2µF
6.3V CERAMIC
C2
1µF
Li+
CELL
0.055Ω, -20V
250mΩ
R3
10kΩ
10V CERAMIC
USB
CHG
USEL
EN
USB INPUT
C1
4.7µF
500mA
100mA
400mΩ
6.3V CERAMIC
R5
100kΩ
REGULATOR
REF
DCI
TO REF
C6
0.1µF
R4
10kΩ
R6
301kΩ
10V CERAMIC
THRM
GND
NTC
THERMISTOR
10kΩ AT +25°C
BYP
PGND
C4
2.2µF
10V CERAMIC
Figure 4. Full-Featured Circuit. Overvoltage protection MOSFET (Q2) on DC withstands up to 18V from the AC adapter, but disables
charging at inputs over 6.2V. Output switch-over MOSFET (Q3) disconnects the battery from the system load when input power is
applied. The input can power the system through D1, D2, Q1, and Q2 when either USB or AC power is present.
14 ______________________________________________________________________________________
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
TO SYSTEM
LOAD
D2
500mA,
SCHOTTKY
(MBR0520L)
OVP UP TO 18V
R2
1kΩ
CHARGING UP TO 6.0V
D5
500mA,
DC
C5
4.7µF
25V CERAMIC
SCHOTTKY
(MBR0520L)
Q2
FDN302
0.055Ω, -20V
Q3
MAX1874
DCOK
PON
FDN302
0.055Ω, -20V
BATT
TO BYP
DCLV
UOK
D4
LED
C2
1µF
10V CERAMIC
C3
2.2µF
Li+
CELL
250mΩ
6.3V CERAMIC
R7
3kΩ
USB
CHG
USEL
EN
USB INPUT
C1
4.7µF
500mA
100mA
400mΩ
6.3V CERAMIC
REGULATOR
TO REF
REF
DCI
C6
0.1µF
R4
10kΩ
10V CERAMIC
THRM
GND
NTC
THERMISTOR
10kΩ AT +25°C
BYP
PGND
C4
2.2µF
10V CERAMIC
Figure 5. Partial-Battery Load Switching. AC adapter power is routed directly to the battery, but USB power is not. When USB power
is connected, total USB current is limited to that set by USEL and system power is drawn from the battery through D5.
Chip Information
TRANSISTOR COUNT: 4997
PROCESS: BICMOS
______________________________________________________________________________________ 15
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
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.)
16 ______________________________________________________________________________________
Dual-Input, USB/AC Adapter, 1-Cell
Li+ Charger with OVP and Thermal Regulation
Package Information (continued)
(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.)
Revision History
Pages changed at Rev 1: 1, 10, 11, 12, 14, 16
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 ____________________ 17
© 2007 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
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