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19-2912; Rev 0; 7/03
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation
General Description
The MAX1874 charges a single-cell Li+ battery from both USB and AC adapter sources. It also includes battery-to-input power switchover, so the system can be powered directly from the power source rather than from the battery. In its simplest application, the MAX1874 needs no external MOSFET or diodes, and accepts input voltages up to 6.5V; however, DC input overvoltage protection up to 18V can be added with a single SOT PFET. On-chip thermal limiting simplifies PC board 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. Ambient or battery temperature can be monitored with an external thermistor. When the temperature is out of range, charging pauses. 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 poweron (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. 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 -40C to +85C temperature range. o Charge from USB* or AC Adapter o Automatic Switchover to AC Adapter o Thermal Limiting Simplifies Board Design o Small, High-Power 16-Pin Thin QFN Package o Input Protection Up to 18V o Soft-Start o Automatic Battery-to-Input Load Switch
*Protected by U.S. Patent #6,507,172.
Features
MAX1874
Ordering Information
PART MAX1874ETE TEMP RANGE PIN-PACKAGE -40C to +85C 16 Thin QFN 5mm x 5mm
Typical Operating Circuit
DC INPUT DC
MAX1874
DCOK DCLV UOK
PON BATT
Li+ CELL
Applications
PDAs Wireless Appliances Cell Phones Digital Cameras
USB INPUT
USB
CHG USEL 500mA 100mA
Pin Configuration
DCOK
TO REF
DCI REGULATOR
EN REF
BATT
PON 14
TOP VIEW
16 DCLV DC CHG USEL 1 2 3 4 5 EN
15
13
UOK
THRM
12 11 USB BYP PGND REF
MAX1874
10 9
BYP
PGND
GND
NTC THERMISTOR
6
GND
7 DCI
8 THRM
THIN QFN 5mm x 5mm
Functional Diagram appears at the end of the data sheet. 1
________________________________________________________________ Maxim Integrated Products
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 MAX1874
ABSOLUTE MAXIMUM RATINGS
DC, DCOK to GND .................................................-0.3V to +20V DCLV, BYP, USB, UOK, DCI, REF, USEL, THRM, 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 Continuous Power Dissipation (TA = +70C) 16-Pin 5mm 5mm Thin QFN (derate 21.3mW/C above +70C) ...................................1.7W Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Maximum Junction Temperature .....................................+150C Lead Temperature (soldering, 10s) .................................+300C
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
(VUSB = VDC = VDCLV = VEN = VUSEL = 5V, VBATT = 4.2V, VTHRM = VREF / 2, Circuit of Figure 2, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER INPUT VOLTAGE RANGES AND INPUT CURRENT Maximum DC Input Voltage with Overvoltage Protection Maximum DC Input Voltage Without Overvoltage Protection Maximum Input Voltage for Charging DC Supply Current DCLV Operating Voltage Range DCLV Shutdown Supply Current USB Input Voltage Range VEN = 0V USB Supply Current DCI Input Current BYP Output Resistance THRM Input Bias Current BATTERY VOLTAGE BATT Regulation Voltage BATT Prequal Voltage Threshold Prequal Threshold Hysteresis USB Charging Headroom DC Charging Headroom REF Voltage (Buffered Output) IUSB = 100mA IUSB = 500mA IDCIN = 800mA IREF = 0 to 500A, 4V < VDC or VUSB < 6.5V; does not affect BATT regulation accuracy 2.94 BATT rising 4.1685 2.8 4.20 3 70 100 200 250 3 3.06 4.2315 3.2 V V mV mV mV V (Note 1) VEN = 5V, VDC = 0V VEN = 5V, VDC = 5V VEN = 0V 4.35 500 2 160 1 5 1 100 VEN = 0V VEN = 5V 4.35 300 Q2 input MOSFET must be in place; charging occurs only below 6.2V, Figures 3, 4, and 5 DC = DCLV, Q2 input MOSFET not on circuit, Figure 2 6.0 6.2 2 4 18 6.5 6.5 4 6 6.00 500 6.50 750 3 300 100 V V V mA V A V A mA A nA nA CONDITIONS MIN TYP MAX UNITS
2
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Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation
ELECTRICAL CHARACTERISTICS (continued)
(VUSB = VDC = VDCLV = VEN = VUSEL = 5V, VBATT = 4.2V, VTHRM = VREF / 2, Circuit of Figure 2, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER BATTERY CHARGING AND PRECHARGE CURRENT DCI Voltage Range DCI Voltage to BATT Current USB Charging Current Soft-Start Current-Ramp Time Prequal Charging Current BATT Input Current BATT Shutdown Current THRM COLD Trip Level THRM HOT Trip Level THRM Disable Threshold Internal Die Thermal Limit LOGIC INPUT/OUTPUTS AND GATE DRIVERS PON High Output Resistance PON Low Output Resistance DCOK Low Output Resistance DCOK Off-Leakage Current UOK Output Resistance UOK Off-Leakage Current CHG Threshold to Indicate Battery Full, Battery Current Falling (Note 3) CHG Logic-Low Output CHG Leakage Current EN, USEL Logic-Input High Level EN, USEL Logic-Input Low Level EN, USEL Input Bias Current PON pulled up to active input (DCLV or USB), VDCLV or VUSB = 5V PON resistance to GND, VDCLV = VUSB = 0 DCOK pulled low V DCOK = 12V, VDC = 0V UOK resistance to GND, VDC = 0 V UOK = 6.5V DC input (% of charge current set at DCI) USB input, USEL = 5V (% of USB charging current) USB input with USEL = 0 Sinking 10mA sink V CHG = 6.5V 1.6 0.4 1 8 20 12.5 25 Voltage mode 0.4 1 V A V V A 25 1 19 30 % 25 120 25 1 k A A VDCI = VREF VDCI = VREF / 2 USEL = high USEL = low Measured from 10% to 90% VBATT = 2.5V No DC or USB power, VBATT = 4.2V EN = GND, USB- and/or DC-powered (Note 2) (Note 2) 0.72 0.28 50 35 0.1 x VREF 950 490 1000 520 455 82 7 55 5 1 0.74 0.29 100 +105 70 7.5 2 0.76 0.30 150 VREF 1050 550 495 95 V mA mA ms mA A A VREF VREF mV C CONDITIONS MIN TYP MAX UNITS
MAX1874
THERMISTOR MONITOR AND DIE-TEMPERATURE REGULATION
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3
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation MAX1874
ELECTRICAL CHARACTERISTICS (continued)
(VUSB = VDC = VDCLV = VEN = VUSEL = 5V, VBATT = 4.2V, VTHRM = VREF / 2, Circuit of Figure 2, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER TIMING DC Rising to DCOK Falling USB Rising to UOK Falling DC Falling to DCOK Going Open-Drain Propagation Delay USB Falling to UOK Going Open-Drain Propagation Delay DC Rising to PON Rising (90%) USB Rising to PON Rising (90%) DC Falling to PON Going Open-Drain Propagation Delay USB Falling to PON Going Open-Drain Propagation Delay USB = open, DC rising to 5V DC = open, USB rising to 5V USB = open, 1k pullup DC = open, 10k pullup USB = open, DC step to 5V, BATT = 3.6V, 100k pulldown DC = open, VUSB step to 5V, VBATT = 3.6V, 100k pulldown USB = open, 100k pulldown DC = open, 100k pulldown 20 20 2 2 20 20 2 2 ms ms s s ms ms s s CONDITIONS MIN TYP MAX UNITS
ELECTRICAL CHARACTERISTICS
(VUSB = VDC = VDCLV = VEN = VUSEL = 5V, VBATT = 4.2V, VTHRM = VREF / 2, Circuit of Figure 2, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 4)
PARAMETER INPUT VOLTAGE RANGES AND INPUT CURRENT Maximum DC Input Voltage with Overvoltage Protection Maximum DC Input Voltage Without Overvoltage Protection Maximum Input Voltage for Charging DC Supply Current DCLV Operating Voltage Range DCLV Shutdown Supply Current USB Input Voltage Range VEN = 0V USB Supply Current DCI Input Current THRM Input Bias Current VEN = 5V, VDC = 0V VEN = 5V, VDC = 5V VEN = 0V 4.35 VEN = 0V VEN = 5V 4.35 Q2 input MOSFET must be in place; charging occurs only below 6.2V, Figures 3, 4, and 5 DC = DCLV, Q2 input MOSFET not on circuit, Figure 3 6.0 18 6.5 6.5 4 6 6.00 500 6.50 750 3 300 100 100 V V V mA V A V A mA A nA nA CONDITIONS MIN TYP MAX UNITS
4
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Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation
ELECTRICAL CHARACTERISTICS (continued)
(VUSB = VDC = VDCLV = VEN = VUSEL = 5V, VBATT = 4.2V, VTHRM = VREF / 2, Circuit of Figure 2, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 4)
PARAMETER BATTERY VOLTAGE BATT Regulation Voltage BATT Prequal Voltage Threshold REF Voltage (Buffered Output) BATT rising IREF = 0 to 500A, 4V < VDC or VUSB < 6.5V; does not affect BATT regulation accuracy 4.1685 2.8 2.94 4.2315 3.2 3.06 V V V CONDITIONS MIN TYP MAX UNITS
MAX1874
BATTERY CHARGING AND PRECHARGE CURRENT DCI Voltage Range DCI Voltage to BATT Current USB Charging Current Prequal Charging Current BATT Input Current BATT Shutdown Current THRM COLD Trip Level THRM HOT Trip Level THRM Disable Threshold LOGIC INPUT/OUTPUTS AND GATE DRIVERS DCOK Off-Leakage Current UOK Off-Leakage Current CHG Threshold to Indicate Battery Full, Battery Current Falling (Note 3) CHG Logic-Low Output CHG Leakage Current EN, USEL Logic-Input High Level EN, USEL Logic-Input Low Level EN, USEL Input Bias Current V DCOK = 12V, VDC = 0V V UOK = 6.5V DC input (% of charge current set at DCI) USB input, USEL = 5V (% of USB charging current) Sinking 10mA sink V CHG = 6.5V 1.6 0.4 1 8 20 1 1 20 30 0.4 1 % V A V V A A A VDCI = VREF VDCI = VREF / 2 USEL = high USEL = low VBATT = 2.5V No DC or USB power, VBATT = 4.2V EN = GND, USB and/or DC powered (Note 2) (Note 2) 0.72 0.28 50 40 0.1 x VREF 930 490 VREF 1070 565 495 95 70 7.5 2 0.76 0.30 150 V mA mA mA A A VREF VREF mV
THERMISTOR MONITOR AND DIE-TEMPERATURE REGULATION
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 +5C accuracy with 5% accuracy of thermistor beta (3450 nominal) with 2C 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 -40C are guaranteed by design, not production tested.
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5
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation MAX1874
Typical Operating Characteristics
(VUSB = VDC = VDCLV = VEN = 5V, VBATT = 4.2V, VTHRM = VREF / 2, VDCI = VREF, VUSEL = 5V, Circuit of Figure 4, TA = +25C, unless otherwise noted.)
DC INPUT CURRENT vs. DC INPUT VOLTAGE
MAX1874 toc01
USB INPUT CURRENT vs. USB INPUT VOLTAGE
MAX1874 toc02
USB INPUT CURRENT vs. USB INPUT VOLTAGE (VEN = 0)
1.4 1.2 1.0
USB (mA)
14 12 10 8 6 4 2 0 0 2 4 6 8
VUSB = 0 VBATT = 4.2V VEN = 5V INCLUDES R2 CURRENT
4.5 4.0 3.5 IUSB (mA) 3.0 2.5 2.0 1.5 1.0 0.5 0
VEN = 5V, VDC FLOATING INCLUDES R3 AND R4 CURRENTS
VEN = 0 INCLUDES R3 AND R4 CURRENTS
IDC (mA)
0.8 0.6 0.4 0.2 0
10 12 14 16 18 20 VDC (V)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
VUSB (V)
VUSB (V)
CHARGE CURRENT vs. DC INPUT-VOLTAGE HEADROOM
MAX1874 toc04
CHARGE CURRENT vs. USB VOLTAGE HEADROOM
MAX1874 toc05
CHARGE CURRENT vs. BATTERY VOLTAGE (IBATT vs. VBATT)
900 800 700 IBATT (mA) 600 500 400 300 200 100 VEN = 5 VUSB = 0 IBATT = SET TO 750mA VDC = VDCLV = 5V
MAX1874 toc06
800 700 DCI SET FOR IBATT = 750mA 600 IBATT (mA) 500 400 300 200 100 0 0
600 500 400 IBATT (mA) 300 200 100 0
1000
0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 (VUSB - VBATT) (V) 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VBATT (V)
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 (VDC - VBATT) (V)
CHARGE CURRENT vs. TEMPERATURE WITH THERMAL REGULATION
VDCI = VREF VDC = 5V VBATT = 3.9V
MAX1874 toc07
CHARGE CURRENT vs. VDCI
MAX1874 toc08
BATTERY TERMINATION VOLTAGE vs. TEMPERATURE
4.24 4.23 4.22 VBATT (V) 4.21 4.20 4.19
MAX1874 toc09
1.2 1.0 0.8 IBATT (A)
1.2 1.0 0.8 IBATT (A) 0.6 0.4 0.2 0
4.25
0.6 0.4 0.2 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
4.18 4.17 4.16 4.15 0 0.5 1.0 1.5 VDCI (V) 2.0 2.5 3.0 -40 -25 -10 5 20 35 50 65 80 TEMPERATURE (C)
6
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MAX1874 toc03
5.0
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation
Typical Operating Characteristics (continued)
(VUSB = VDC = VDCLV = VEN = 5V, VBATT = 4.2V, VTHRM = VREF / 2, VDCI = VREF, VUSEL = 5V, Circuit of Figure 4, TA = +25C, unless otherwise noted.)
OFF-BATTERY LEAKAGE vs. USB INPUT VOLTAGE
MAX1874 toc10
MAX1874
OFF-BATTERY LEAKAGE vs. DC INPUT VOLTAGE
MAX1874 toc11
USB LEAKAGE vs. DC INPUT VOLTAGE
LEAKAGE FROM USB TO GND VEN = 5V
MAX1874 toc12
10 9 8 7 IBATT OFF (A) VEN = 0 VDCLV = VDC = 0 VBATT = 4.2V
10 9 8 7 IBATT OFF (A) 6 5 4 3 2 1 0 VEN = 0 VUSB = 0 VBATT = 4.2V VDC = VDCLV
600 500 400 300 200 100 0
6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 VUSB (V)
0
1
2
3
4
5
6
7
IUSB OFF (nA)
0
2
4
6
8
10
12
14
16
18
VDCIN (V)
VDCIN (V)
BATTERY CURRENT AND VOLTAGE vs. TIME
1000 900 800 700 IBATT (A) 600 500 400 300 200 100 0 0 50 100 150 TIME (MIN) 200 250 VBATT CHG IBATT
MAX1874 toc13
RESPONSE TO OVERVOLTAGE INPUT USB = 0
8.0 7.2 6.4 VBATT AND VCHG (V) 5.6 4.8 4.0 3.2 2.4 1.6 0.8 0 300 40ms/div 20V/div DC 10V/div 5V/div 5V/div DCLV PON 1A/div 20V/div DCOK 10V/div 10V/div
MAX1874 toc14
DC CONNECT WAVEFORMS VUSB = 0, VBATT = 3.9V
10V/div
MAX1874 toc15
1.5AHr CELL
DC
DCLV PON
IBATT DCOK
40ms/div
DC CONNECT WAVEFORMS VUSB = 5V, VBATT = 3.9V
10V/div
MAX1874 toc16
USB CONNECT WAVEFORMS VDC = 0, VBATT = 3.9V
DC 5V/div
DC STARTUP WAVEFORMS FOR ENABLE VBATT = 3.9V
MAX1874 toc18
MAX1874 toc17
USB
5V/div
EN
10V/div 10V/div
DCLV PON 5V/div PON 5V/div CHG
1A/div 10V/div
IBATT 500mA/div DCOK 5V/div
IBATT 500mA/div UOK 10ms/div IBATT
40ms/div
40ms/div
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7
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation MAX1874
Pin Description
PIN 1 2 NAME DCLV DC CHG 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. 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). 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. Enable/Disable Input. Drive EN high to enable the device. When EN is low, UOK, DCOK, PON, and REF remain active. 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 (10k at +25C) is at less than 0C or greater than +50C. Connect to GND to disable. See the External Thermistor Monitor (THRM) section. 3V Reference Output. Sources up to 500A to bias IDCI and external thermistor. Bypass with 0.1F to GND. REF loading does not affect BATT regulation accuracy. 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 2.2F capacitor to GND. 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. PON is an active-high, open-drain output with an internal 120k resistor to ground that goes high when VDC or VUSB > VBATT. PON can directly drive an external PFET that disconnects the battery from the system load when power is applied. Charge Output. Connect to the positive terminal of the Li+ battery. DCOK is an active-low, open-drain output that goes low when 3.5V < VDC < 6.2V.
3
4 5 6 7 8 9 10 11 12 13
USEL EN GND DCI THRM REF PGND BYP USB UOK
14 15 16
PON BATT DCOK
8
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Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation
Functional Diagram
MAX1874
BYP DC OVERVOLTAGE AND UNDERVOLTAGE DETECT DCOK INPUT POWEROK SELECT N 120k 5
5 PON
DCLV USB 0.25 0.4
BATT
USB/DCLV DETECT IUSB_SENSE UOK IDCLV_SENSE LINEAR REGULATOR
MAX1874
VBATT
CHG
N TEMPERATURE
N
DCI USEL
THERMISTOR COMPARATORS
3.00V REFERENCE
REF
GND
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9
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation MAX1874
Detailed Description
The MAX1874 charges a single-cell Li+ battery from either USB power sources or AC adapter sources. It contains a complete two-input linear charger that controls both battery charge current and voltage. In addition to all charging functions, the MAX1874 includes voltagesensing 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 regulated 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. The MAX1874 also features a thermal regulation loop that adjusts charging current so the die temperature remains below +105C. See the Package Thermal Limiting section. This on-chip thermal control simplifies PC board layout and allows the optimum charging rate to be set without the thermal limits imposed by worstcase battery and input voltage. When the MAX1874 thermal limit is reached, the charger does not shut down but reduces charging current. In addition to, and separate from, its internal die temperature control, the MAX1874 can also monitor ambient or cell temperature with an external thermistor connected to THRM. When the thermistor temperature is out of range (greater than +50C or less than 0C), charging stops until the temperature returns to normal. See the External Thermistor Monitor (THRM) section. 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). When charging is stopped or input power is removed, battery leakage is typically 5A. 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 100mA through the USEL input. When power is taken from the DC input, charge current is linearly set by the voltage at DCI. The MAX1874 charge current can also be DAC controlled with the output of a DAC connected to DCI. See the Charging Current section.
Enable (EN)
The enable input, EN, switches the MAX1874 on or off. With EN high, the MAX1874 is on and can begin charging. 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. DC serves as the sense input for the adapter power source. This input senses when DC is above 6.2V (maximum 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. 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.
DC Power-OK (DCOK)
DCOK is an active-low, open-drain output that goes low when VDC is below 6.2V or above 3.5V. DCOK can be 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 external 1k pullup resistor keeps DCOK high (external MOSFET off) until it is certain the voltage is within the
Table 1. USB and DC Input Selection
VDC > 18V OR VUSB > 6.5V Exceeds operating input range. Not allowed. See the Absolute Maximum Ratings section. 4V < VDC < 6.2V AND 0 < VUSB < 6.5V DCLV powers device and supplies charging current. 1) 2) 4V < VUSB < 6.5V AND VDC < 4V OR VDC > 6.2V USB powers device and supplies charging current. DCLV disconnected from DC source through external MOSFET (Q2 Figures 3, 4, and 5). VDC < 4V OR VDC > 6.2V, AND VUSB < 4V
No charging
Note: VDC takes precedence when both inputs are valid. 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 connecting 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 ratio from DCI to BATT is 1A/VREF. The DCI pin should be connected to a resistive divider from REF to DCI to GND (R5 and R6 in Figures 2 and 4). In this configuration, IBATT is as follows: IBATT = [R6 / (R5 + R6)] Amps R5 and R6 should total 25k or more to minimize loading on REF. Connecting DCI directly to REF results in a 1A charge current.
MAX1874
USB Power-OK (UOK)
UOK is an active-low, open-drain output that goes low to indicate that VUSB is valid (greater than 4V). UOK remains operational when EN is low (charger off). An external 10k 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).
Bypass (BYP)
BYP is the bypass connection for the MAX1874's internal power rail. Bypass to GND with a 2.2F or greater capacitor. The voltage at BYP is supplied from either DCLV or USB through an internal 5 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 (VBATT near 4.2V). The CHG current threshold is a function of the charger mode. When charging from a DC source, CHG goes high when IBATT falls to 12.5% of the current set by VDCI and the charger is in voltage mode (VBATT near 4.2V). When charging from a USB source with USEL high, CHG goes high when IBATT falls to 125mA and the charger is in voltage mode. If the MAX1874 is charging from a USB source with USEL low, CHG goes high when the charger enters voltage mode.
Power On (PON)
PON goes high when VDC or VUSB is within its normal 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.
Charging Current
Precharge Current When the MAX1874 is powered with a battery connected, the IC first detects if the cell voltage is ready for full charge current. If the cell voltage is less than the prequal 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. 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 typically supply 500mA, while unpowered hubs supply
Package Thermal Limiting
On-chip thermal limiting in the MAX1874 simplifies PC board layout and allows charging rates to be automatically optimized without constraints imposed by worstcase 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 +105C.
Table 2. CHG Battery Full Indication
CHARGING SOURCE DCLV Charging USB Charging 500mA (USEL high) USB Charging 100mA (USEL low) 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 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 PC board. 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 MAX1874 thermal resistance from the die to the package thermal pad is typically 5C/W. The thermal resistance of 1in2 of 1oz copper on typical FR4 PC board material in free air is +42C/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 +105C die temperature. With the example thermal resistance of +47C/W, the MAX1874 charge-current thermal limiting can be expected to occur when dissipating approximately 1.7W at +25C ambient, and when dissipating approximately 0.75W at +70C ambient. The power dissipated in the charger is PDISS = [VIN (either VUSB or VDCLV) - VBATT] ICHARGE. Power dissipation drops as the battery voltage rises, so thermalcharge current limiting, if it occurs, typically releases soon after charging begins and has little impact on charge time.
MAX1874
REF 0.1F 10k THRM TCOLD THERMISTOR 10K AT +25C 100mV TO REGULATOR
THOT
Figure 1. Thermistor Sensing Block Diagram
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 connected 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 immediately 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 battery. When system power is taken from the DC or USB input source, use D1, D2, Q1, and Q2 (Figure 4). A partial approach to battery-load switching can connect 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 threshold listed in Table 2, then CHG does not go high to indicate a full battery.
External Thermistor Monitor (THRM)
The MAX1874 features an internal window comparator to monitor battery pack temperature or ambient temperature with an external negative temperature coefficient thermistor. In typical systems, temperature is monitored to prevent charging at ambient temperature extremes (below 0C or above +50C). When the temperature moves outside these limits, charging is stopped. If the VTHERM returns to within its normal window, charging 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 discussed in the Package Thermal Limiting section. The input thresholds for the THRM input are 0.74 VREF for the COLD trip point and 0.29 VREF for the 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 VDC exceeds 6.2V, the DCOK output turns the P-channel MOSFET off. On power-up, DCOK remains high until it has been verified that VDC is in range. If protection 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 MAX1874
DC INPUT UP TO 6.0V C5 4.7F 10V CERAMIC DC DCOK
MAX1874
PON BATT C3 2.2F 6.3V CERAMIC Li+ CELL
DCLV UOK 250m USB
USB INPUT
C1 4.7F 6.3V CERAMIC R5 100k
CHG 400m USEL EN 500mA 100mA REGULATOR
TO REF R6 301k
DCI
REF
C6 0.1F 10V CERAMIC
R4 10k
THRM NTC THERMISTOR 10k AT +25C
BYP C4 2.2F 10V CERAMIC
PGND
GND
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 1k 5% Q2 FDN302 0.055, -20V
0VP UP TO 18V CHARGING UP TO 6.0V C5 4.7F 25V CERAMIC
DC DCOK
MAX1874
PON BATT C3 2.2F 6.3V CERAMIC Li+ CELL
DCLV C2 1F 10V CERAMIC UOK 250m USB
USB INPUT
C1 4.7F 6.3V CERAMIC
CHG 400m USEL EN 500mA 100mA REGULATOR
TO REF
DCI
REF
C6 0.1F 10V CERAMIC
R4 10k
THRM NTC THERMISTOR 10k AT +25C BYP C4 2.2F 10V CERAMIC PGND GND
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 MAX1874
D2 500mA, SCHOTTKY (MBR0520L) DC DCOK TO SYSTE LOAD
OVP UP TO 18V CHARGING UP TO 6.0V C5 4.7F 25V CERAMIC D1 500mA, SCHOTTKY (MBR0520L) Q1 FDN302 0.055, -20V R3 10k USB INPUT Q2 FDN302 0.055, -20V
R2 1k
MAX1874
PON BATT C3 2.2F 6.3V CERAMIC
Q3 FDN302 0.055, -20V
DCLV UOK C2 1F 10V CERAMIC USB C1 4.7F 6.3V CERAMIC R5 100k TO REF R6 301k DCI 250m
Li+ CELL
CHG 400m USEL EN REGULATOR REF 500mA 100mA
C6 0.1F 10V CERAMIC
R4 10k
THRM NTC THERMISTOR 10k AT +25C BYP C4 2.2F 10V CERAMIC PGND GND
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 MAX1874
TO SYSTEM LOAD
OVP UP TO 18V CHARGING UP TO 6.0V C5 4.7F 25V CERAMIC Q2 FDN302 0.055, -20V
R2 1k
D2 500mA, SCHOTTKY (MBR0520L) DC DCOK Q3 FDN302 0.055, -20V
MAX1874
PON BATT C3 2.2F 6.3V CERAMIC
D5 500mA, SCHOTTKY (MBR0520L)
DCLV C2 1F 10V CERAMIC UOK 250m USB
TO BYP Li+ CELL
D4 LED
R7 3k
USB INPUT
C1 4.7F 6.3V CERAMIC
CHG 400m USEL EN 500mA 100mA REGULATOR
TO REF
DCI
REF
C6 0.1F 10V CERAMIC
R4 10k
THRM NTC THERMISTOR 10k AT +25C BYP C4 2.2F 10V CERAMIC PGND GND
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 MAX1874
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.)
QFN THIN.EPS
L
REV.
0.15 C A
D2
C L
D
b D2/2
0.10 M C A B
PIN # 1 I.D.
D/2
0.15 C B
k
PIN # 1 I.D. 0.35x45
E/2 E2/2 E (NE-1) X e
C L
E2
k L
DETAIL A
e (ND-1) X e
C L
C L
L
e 0.10 C A 0.08 C
e
C
A1 A3
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL DOCUMENT CONTROL NO.
21-0140
C
1 2
COMMON DIMENSIONS
EXPOSED PAD VARIATIONS
NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220. 10. WARPAGE SHALL NOT EXCEED 0.10 mm.
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL DOCUMENT CONTROL NO. REV.
21-0140
C
2 2
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 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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