Detailed Description

The MAX745 is a switch-mode, Li+ 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 connections 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 accuracy 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 through the SETI and VADJ pins.

Whether the MAX745 is controlling voltage or current

at any time depends on the battery state. If the battery

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 voltage.

The STATUS pin indicates whether the charger is regulat-

ing current or voltage.

Voltage Control

To set the voltage limit on the battery, connect a resis-

at 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

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

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

4

CCV

Voltage-Regulation-Loop Compensation Point

5

CCI

Current-Regulation-Loop Compensation Point

6

THM/

SHDN

Thermistor Sense-Voltage Input. THM/SHDN also performs the shutdown function.

If pulled low, the charger turns off.

7

REF

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

8

VADJ

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

9

SETI

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

10

GND

Analog Ground

11, 12

CELL1,

CELL0

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

13

STATUS

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

voltage-regulation mode. Connect STATUS to VL through a 1kΩ to 100kΩ pullup resistor. STATUS can also

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

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

MAX745

Switch-Mode Lithium-Ion

Battery-Charger

www.maximintegrated.com

Maxim Integrated │ 5

Pin Description