_______________Detailed Description

The MAX745 is a switch-mode, lithium-ion battery

charger that can achieve 90% efficiency. The charge

voltage and current are set independently by external

resistor-dividers at SETI and VADJ, and at pin connec-

tions at CELL0 and CELL1. VADJ is connected to a

resistor-divider to set the charging voltage. The output

voltage-adjustment range is ±5%, eliminating the need

for 0.1% resistors while still achieving 0.75% set accu-

racy using 1% resistors.

The MAX745 consists of a current-mode, pulse-width-

modulated (PWM) controller and two transconductance

error amplifiers: one for regulating current (GMI) and

the other for regulating voltage (GMV) (Figure 2). The

error amplifiers are controlled via the SETI and VADJ

pins. Whether the MAX745 is controlling voltage or cur-

rent at any time depends on the battery state. If the bat-

tery is discharged, the MAX745 output reaches the

current-regulation limit before the voltage limit, causing

the system to regulate current. As the battery charges,

the voltage rises to the point where the voltage limit is

reached and the charger switches to regulating volt-

age. The STATUS pin indicates whether the charger is

regulating current or voltage.

Voltage Control

To set the voltage limit on the battery, tie a resistor-

VADJ sets a ±5% change in the battery limit voltage

around 4.2V. Since the 0 to 4.2V range on VADJ results

in only a 10% change on the voltage limit, the resistor-

divider’s accuracy does not need to be as high as the

output voltage accuracy. Using 1% resistors for the

voltage dividers typically results in no more than 0.1%

degradation in output voltage accuracy. VADJ is inter-

nally buffered so that high-value resistors can be used

to set the output voltage. When the voltage at VADJ is

Switch-Mode Lithium-Ion

Battery Charger

_______________________________________________________________________________________

5

______________________________________________________________Pin Description

IBAT

Current-Sense Amplifier’s Analog Current-Source Output. See

Monitoring Charge Current section for

detailed description.

2

DCIN

Charger Input Voltage. Bypass DCIN with a 0.1µF capacitor.

3

VL

Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL with a 4.7µF capacitor.

1

4

CCV

Voltage-Regulation-Loop Compensation Point

5

CCI

Current-Regulation-Loop Compensation Point

8

VADJ

Voltage-Adjustment Pin. VADJ is tied to a 1% tolerance external resistor-divider to adjust the voltage set

7

REF

4.2V Reference Voltage Output. Bypass REF with a 0.1µF or greater capacitor.

6

THM/

SHDN

Thermistor Sense-Voltage Input. THM/SHDN also performs the shutdown function. If pulled low,

the charger turns off.

13

STATUS

An open-drain MOSFET sinks current when in current-regulation mode, and is high impedance when in volt-

age-regulation mode. Connect STATUS to VL through a 1k

Ω to 100kΩ pull-up resistor. STATUS may also drive

an LED for visual indication of regulation mode (see MAX745 evaluation kit). Leave STATUS floating if not used.

11, 12

CELL1,

CELL0

Logic Inputs to Select Cell Count. See Table 1 for cell-count programming.

10

GND

Analog Ground

9

SETI

SETI is externally tied to the resistor-divider between REF and GND to set the charging current.

14

BATT

Battery-Voltage-Sense Input and Current-Sense Negative Input

15

CS

Current-Sense Positive Input

16

PGND

Power Ground

17

DLO

Low-Side Power MOSFET Driver Output

18

DHI

High-Side Power MOSFET Driver Output

19

LX

Power Connection for the High-Side Power MOSFET Source

20

BST

Power Input for the High-Side Power MOSFET Driver

NAME

FUNCTION

PIN