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General Description

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.

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.

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 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.

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.

Applications

PDAs Cell Phones

Wireless Appliances Digital Cameras

Features

♦ 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

♦ Soft-Start

♦ Automatic Battery-to-Input Load Switch

*Protected by U.S. Patent #6,507,172.

MAX1874

Dual-Input, USB/AC Adapter, 1-Cell

Li+ Charger with OVP and Thermal Regulation

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

19-2912; Rev 0; 7/03

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.

PART TEMP RANGE PIN-PACKAGE

MAX1874ETE -40°C to +85°C 16 Thin QFN 5mm x 5mm

16 15 14 13

DCOK

BATT

PON

UOK

REF

PGND

BYP

USB

USEL

CHG

DCLV

5678

GND

DCI

THRM

MAX1874

THIN QFN

5mm x 5mm

TOP VIEW

Pin Configuration

Functional Diagram appears at the end of the data sheet.

MAX1874

USB INPUT

DC INPUT

TO REF

DCLV

GND

BATT

NTC

THERMISTOR

PON

REF

THRM

USB

Li+

CELL

USEL

500mA

100mA

ENDCI

PGND

BYP

REGULATOR

UOK

CHG

DCOK

Typical Operating Circuit

Summary of content (16 pages)

PAGE 1
9-2912; Rev 0; 7/03 Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation 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.
PAGE 2
MAX1874 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 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) .....................
PAGE 3
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation (VUSB = VDC = VDCLV = VEN = VUSEL = 5V, VBATT = 4.2V, VTHRM = VREF / 2, Circuit of Figure 2, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS VREF V BATTERY CHARGING AND PRECHARGE CURRENT DCI Voltage Range 0.
PAGE 4
MAX1874 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 = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 5
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation (VUSB = VDC = VDCLV = VEN = VUSEL = 5V, VBATT = 4.2V, VTHRM = VREF / 2, Circuit of Figure 2, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 4) PARAMETER CONDITIONS MIN TYP MAX UNITS 4.1685 BATTERY VOLTAGE BATT Regulation Voltage 4.2315 V BATT Prequal Voltage Threshold BATT rising 2.8 3.2 V REF Voltage (Buffered Output) IREF = 0 to 500µA, 4V < VDC or VUSB < 6.
PAGE 6
Typical Operating Characteristics (VUSB = VDC = VDCLV = VEN = 5V, VBATT = 4.2V, VTHRM = VREF / 2, VDCI = VREF, VUSEL = 5V, Circuit of Figure 4, TA = +25°C, unless otherwise noted.) USB INPUT CURRENT vs. USB INPUT VOLTAGE IUSB (mA) 6 1.2 1.0 3.0 2.5 2.0 0.8 0.6 1.5 4 VEN = 0 INCLUDES R3 AND R4 CURRENTS 1.4 3.5 8 MAx1874 toc03 4.0 10 IDC (mA) VEN = 5V, VDC FLOATING INCLUDES R3 AND R4 CURRENTS 4.5 USB (mA) 12 5.0 MAX1874 toc01 VUSB = 0 VBATT = 4.
PAGE 7
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation OFF-BATTERY LEAKAGE vs. DC INPUT VOLTAGE 8 8 IBATT OFF (µA) IBATT OFF (µA) 6 5 4 6 5 4 3 3 2 2 1 1 0 1 2 3 4 5 0 1 2 3 4 5 6 7 0 2 4 6 8 10 12 14 VUSB (V) VDCIN (V) VDCIN (V) BATTERY CURRENT AND VOLTAGE vs. TIME RESPONSE TO OVERVOLTAGE INPUT USB = 0 DC CONNECT WAVEFORMS VUSB = 0, VBATT = 3.9V MAX1874 toc13 1000 1.5AHr CELL 900 IBATT 7.2 5.6 600 4.8 500 4.0 400 3.2 VBATT 300 2.
PAGE 8
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation MAX1874 Pin Description PIN 8 NAME 1 DCLV 2 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. Voltage-Sense Pin for DC Input from AC Adapter. Maximum operating voltage at this pin is 18V.
PAGE 9
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation BYP 5Ω DC OVERVOLTAGE AND UNDERVOLTAGE DETECT 5Ω INPUT POWEROK SELECT DCOK PON N 120kΩ DCLV BATT 0.25Ω USB 0.4Ω MAX1874 USB/DCLV DETECT VBATT IUSB_SENSE IDCLV_SENSE UOK N CHG LINEAR REGULATOR N TEMPERATURE DCI USEL 3.
PAGE 10
MAX1874 Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation 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.
PAGE 11
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation 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 10kΩ pullup resistor keeps UOK high until it is certain that power is within the acceptable range.
PAGE 12
MAX1874 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 5°C/W.
PAGE 13
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation MAX1874 DC INPUT UP TO 6.0V DC C5 4.7µF 10V CERAMIC MAX1874 DCOK PON BATT DCLV C3 2.2µF 6.3V CERAMIC UOK 250mΩ USB USB INPUT C1 4.7µF 6.3V CERAMIC Li+ CELL CHG 500mA USEL 400mΩ 100mA EN R5 100kΩ TO REF REGULATOR DCI REF C6 0.1µF 10V CERAMIC R6 301kΩ R4 10kΩ THRM BYP NTC THERMISTOR 10kΩ AT +25°C GND PGND C4 2.2µF 10V CERAMIC Figure 2.
PAGE 14
MAX1874 Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation OVP UP TO 18V CHARGING UP TO 6.0V C5 4.7µF 25V CERAMIC R2 1kΩ D1 500mA, SCHOTTKY (MBR0520L) Q2 FDN302 0.055Ω, -20V D2 500mA, SCHOTTKY (MBR0520L) TO SYSTE LOAD DC MAX1874 DCOK BATT DCLV Q1 FDN302 0.055Ω, -20V C3 2.2µF 6.3V CERAMIC UOK R3 10kΩ C2 1µF 10V CERAMIC 250mΩ USB USB INPUT C1 4.7µF 6.3V CERAMIC Q3 FDN302 0.
PAGE 15
Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation C5 4.7µF 25V CERAMIC R2 1kΩ Q2 FDN302 0.055Ω, -20V DC MAX1874 DCOK BATT DCLV C2 1µF 10V CERAMIC USB C1 4.7µF 6.3V CERAMIC D5 500mA, SCHOTTKY (MBR0520L) TO BYP C3 2.2µF 6.3V CERAMIC UOK 250mΩ USB INPUT Q3 FDN302 0.055Ω, -20V PON MAX1874 OVP UP TO 18V CHARGING UP TO 6.0V TO SYSTEM LOAD D2 500mA, SCHOTTKY (MBR0520L) Li+ CELL D4 LED R7 3kΩ CHG USEL 400mΩ 500mA 100mA EN TO REF REGULATOR DCI REF C6 0.
PAGE 16
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.) D2 0.15 C A D b CL 0.10 M C A B D2/2 D/2 PIN # 1 I.D. QFN THIN.EPS MAX1874 Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation k 0.15 C B PIN # 1 I.D. 0.35x45 E/2 E2/2 CL (NE-1) X e E E2 k L DETAIL A e (ND-1) X e CL CL L L e e 0.10 C A C 0.