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MAX846AC

Cost-Saving Multichemistry Battery-Charger System

Maxim Integrated 

Cost-Saving Multichemistry

Battery-Charger System

______________________________________________________________Pin Description

PIN

NAME

FUNCTION

1

DCIN

Supply Input from External DC Source. 3.7V ≤ VDCIN ≤ 20V.

2

VL

3.3V, 20mA, 1% Linear-Regulator Output. VL powers the system µC and other components. Bypass to

GND with a 4.7µF tantalum or ceramic capacitor.

3

CCI

Current-Regulation-Loop Compensation Pin. Connect a compensation capacitor (typically 10nF) from

CCI to VL.

4

GND

Ground

5

CCV

Voltage-Regulation-Loop Compensation Pin. Connect a compensation capacitor (typically 10nF) from

CCV to VL.

6

VSET

Float-Voltage Reference-Adjust Input. Leave VSET open for a 4.2V default. See the Applications

Information section for adjustment information.

Current-Set Input/Current-Monitor Output. ISET sets the current-regulation point. Connect a resistor

from ISET to GND to monitor the charging current. ISET voltage is regulated at 1.65V by the current-

7

ISET

regulation loop. To adjust the current-regulation point, either modify the resistance from ISET to ground

or connect a fixed resistor and adjust the voltage on the other side of the resistor (Figure 5). The

transconductance of the current-sense amplifier is 1mA/V.

8

OFFV

Logic Input that disables the voltage-regulation loop. Set OFFV high for NiCd or NiMH batteries.

9

PWROK

Open-Drain, Power-Good Output to µC. PWROK is low when VL is less than 3V. The reset timeout peri-

od can be set externally using an RC circuit (Figure 3).

10

CELL2

Digital Input. CELL2 programs the number of Li-Ion cells to be charged. A high level equals two cells; a

low level equals one cell.

11

ON

Charger ON/OFF Input. When low, the driver section is turned off and IBATT <1µA. The VL regulator is

always active.

12

BATT

Battery Input. Connect BATT to positive battery terminal.

13

CS+

Current-Sense Amplifier High-Side Input. Connect CS+ to the sense resistor’s power-source side. The

sense resistor may be placed on either side of the pass transistor.

14

CS-

Current-Sense Amplifier Low-Side Input. Connect CS- to the sense resistor’s battery side.

15

PGND

Power Ground

16

DRV

External Pass Transistor (P-channel MOSFET or PNP) Base/Gate Drive Output. DRV sinks current only.

_______________Detailed Description

The MAX846A battery-charging controller combines

three functional blocks: a 3.3V precision, low-dropout

linear regulator (LDO), a precision voltage reference,

and a voltage/current regulator (Figure 1).

Linear Regulator

The LDO regulator output voltage (VL) is two times the

internal reference voltage; therefore, the reference and

LDO track. VL delivers up to 20mA to an external load

and is short-circuit protected. The power-good output

(PWROK) provides microcontroller (µC) reset and

charge-current inhibition.

Voltage Reference

The precision internal reference provides a voltage to

accurately set the float voltage for lithium-ion (Li-Ion)

battery charging. The reference output connects in

series with an internal, 2%-accurate, 20kΩ resistor. This

allows the float voltage to be adjusted using one exter-

nal 1% resistor (RVSET) to form a voltage divider

(Figure 4). The float-voltage accuracy is important for

battery life and to ensure full capacity in Li-Ion batter-

ies. Table 1 shows the accuracies attainable using the

MAX846A.

6 _______________________________________________________________________________________

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