Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - battery management Charge management Li-Ion SSOP 20 Surface-mount

MAX745

Switch-Mode Lithium-Ion

Battery-Charger

________________________________________________________________ Maxim Integrated Products 1

General Description

The MAX745 provides all functions necessary for

charging lithium-ion (Li+) battery packs. It provides a

regulated charging current of up to 4A without getting

hot, and a regulated voltage with only ±0.75% total

error at the battery terminals. It uses low-cost, 1% resis-

tors to set the output voltage, and a low-cost N-channel

MOSFET as the power switch.

The MAX745 regulates the voltage set point and charg-

ing current using two loops that work together to transi-

tion smoothly between voltage and current regulation.

The per-cell battery voltage regulation limit is set

between 4V and 4.4V using standard 1% resistors, and

then the number of cells is set from 1 to 4 by pin-strap-

ping. Total output voltage error is less than ±0.75%.

For a similar device with an SMBus™ microcontroller

interface and the ability to charge NiCd and NiMH cells,

refer to the MAX1647 and MAX1648. For a low-cost Li+

charger using a linear-regulator control scheme, refer

to the MAX846A.

________________________Applications

Li+ Battery Packs

Desktop Cradle Chargers

Cellular Phones

Notebook Computers

Hand-Held Instruments

____________________________Features

♦ Charges 1 to 4 Li+ Battery Cells

♦ ±0.75% Voltage-Regulation Accuracy

Using 1% Resistors

♦ Provides up to 4A without Excessive Heating

♦ 90% Efficient

♦ Uses Low-Cost Set Resistors and

N-Channel Switch

♦ Up to 24V Input

♦ Up to 18V Maximum Battery Voltage

♦ 300kHz Pulse-Width Modulated (PWM) Operation

Low-Noise, Small Components

♦ Stand-Alone Operation—No Microcontroller

Needed

Typical Operating Circuit

19-1182; Rev 3; 10/01

PART

MAX745EAP -40°C to +85°C

TEMP RANGE PIN-PACKAGE

20 SSOP

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

Ordering Information

Pin Configuration appears at end of data sheet.

MAX745C/D 0°C to +70°C Dice*

*Dice are tested at T

= +25°C.

SMBus is a trademark of Intel Corp.

(UP TO 24V)

REF

DCIN

BST

DHI

DLO

BATT

CELL

COUNT

SELECT

SET PER

CELL VOLTAGE

WITH 1% RESISTORS

OFF

VADJ

STATUS

SETI

CELL0

CELL1

CCI PGNDGND

IBAT

CCV

CHARGE

SENSE

VOUT

1–4 Li+ CELLS

(UP TO 18V)

MAX745

THM/SHDN

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.

Summary of content (8 pages)

PAGE 1
9-1182; Rev 3; 10/01 L MANUA ION KIT HEET T A U L EVA TA S WS DA FOLLO Switch-Mode Lithium-Ion Battery-Charger ____________________________Features ♦ Charges 1 to 4 Li+ Battery Cells ♦ ±0.
PAGE 2
MAX745 Switch-Mode Lithium-Ion Battery Charger ABSOLUTE MAXIMUM RATINGS DCIN to GND ............................................................-0.3V to 26V BST, DHI to GND ......................................................-0.3V to 30V BST to LX ....................................................................-0.3V to 6V DHI to LX............................................(LX - 0.3V) to (BST + 0.3V) LX to GND ................................................-0.3V to (DCIN + 0.3V) VL to GND..........
PAGE 3
Switch-Mode Lithium-Ion Battery Charger (VDCIN = 18V, VBATT = 8.4V, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS ERROR AMPLIFIERS GMV Amplifier Transconductance 800 µA/V GMI Amplifier Transconductance 200 µA/V GMV Amplifier Output Current ±130 µA GMI Amplifier Output Current ±320 µA CCI Clamp Voltage with Respect to CCV 1.1V < VCCV < 3.5V 25 80 200 mV CCV Clamp Voltage with Respect to CCI 1.1V < VCCI < 3.
PAGE 4
__________________________________________Typical Operating Characteristics (TA = +25°C, VDCIN = 18V, VBATT = 4.2V, CELL0 = CELL1 = GND, CVL = 4.7µF CREF = 0.1µF. Circuit of Figure 1, unless otherwise noted.) CURRENT-SENSE VOLTAGE vs. SETI VOLTAGE BATTERY VOLTAGE vs. CHARGING CURRENT 3.0 2.5 2.0 1.5 1.0 R1 = 0.2Ω R16 = SHORT R12 = OPEN CIRCUIT 0.5 0 0 160 140 120 100 80 60 40 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.5 1.5 2.0 2.5 3.0 SETI VOLTAGE (V) REFERENCE VOLTAGE vs.
PAGE 5
Switch-Mode Lithium-Ion Battery Charger PIN NAME FUNCTION 1 IBAT Current-Sense Amplifier’s Analog Current-Source Output. See the Monitoring Charge Current section for a detailed description. 2 DCIN Charger Input Voltage. Bypass DCIN with a 0.1µF capacitor. 3 VL 4 CCV Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL with a 4.7µF capacitor.
PAGE 6
MAX745 Switch-Mode Lithium-Ion Battery Charger VREF / 2, the voltage limit is 4.2V. Table 1 defines the battery cell count. The battery limit voltage is set by the following:    1 VREF     VADJ − 2   VBATT = cell count x  VREF +   9.523     ( ) Solving for VADJ, we get: 9.523 VBATT VADJ = − 9.023VREF (cell count) where VREF = 4.2V and cell count is 1, 2, 3, 4 (Table 1). The voltage-regulation loop is compensated at the CCV pin.
PAGE 7
Switch-Mode Lithium-Ion Battery Charger ICHG = IFS (VSETI / VREF) A capacitor at CCI sets the current-feedback loop’s dominant pole. While the current is in regulation, CCV voltage is clamped to within 80mV of the CCI voltage. This prevents the battery voltage from overshooting when the voltage setting is changed. The converse is true when the voltage is in regulation and the current setting is changed. Since the linear range of CCI or CCV is about 2V (1.5V to 3.
PAGE 8
MAX745 Switch-Mode Lithium-Ion Battery Charger MOSFET Drivers Minimum Input Voltage The MAX745 drives external N-channel MOSFETs to switch the input source generating the battery voltage or current. Since the high-side N-channel MOSFET’s gate must be driven to a voltage higher than the input source voltage, a charge pump is used to generate such a voltage. The capacitor (C7) charges through D2 to approximately 5V when the synchronous rectifier (M1B) turns on (Figure 1).