MAX846ACSLASHD datasheet(9/12 Pages) MAXIM

9 / 12 page

Cost-Saving Multichemistry

Battery-Charger System

_______________________________________________________________________________________

where VX is either GND or VL, and VF is the per-cell

float voltage. In the circuit of Figure 1, RVSET is

400k

Ω. RVSET and the internal 20kΩ resistor form a

divider, resulting in an adjustment range of approxi-

mately ±5%.

The current-regulation loop attempts to maintain the

voltage on ISET at 1.65V. Selecting resistor RISET deter-

mines the reflected voltage required at the current-

sense amplifier input.

• Calculate RCS and RISET as follows:

RCS = VCS / IBATT

RISET (in kΩ) = 1.65V / VCS

where the recommended value for VCS is 165mV.

• Connect ON to PWROK to prevent the charge current

from turning on until the voltages have settled.

Minimize power dissipation in the external pass transis-

tor. Power dissipation can be controlled by setting the

DCIN input supply as low as possible, or by making

VDCIN track the battery voltage.

Microprocessor-Controlled

Multichemistry Operation

The MAX846A is highly adjustable, allowing for simple

interfacing with a low-cost µC to charge Ni-based and

Li-Ion batteries using one application circuit (Figure 3).

= 20k

4.2

1.65

4.2

VSET

Ω

−













MAX846A

IBATT

CCI

GND

CCV

EXTERNAL PASS TRANSISTOR

CAN BE EITHER PNP OR PMOS FET.

OFFV

PGND

DRV

BATT

CS-

(

)

10nF

0.165V

CS+

DCIN

3.7V TO 20V

ISET

CELL2

PWROK

DCIN

VSET

100k

RVSET

ADJUST

(UP)

(DOWN)

10k

RISET

(2 CELLS)

(1 CELL)

0.01

µF

4.7

µF

0.01

µF

RDRV

660

Ω

RCS

4.7

µF

Figure 2. Stand-Alone Li-Ion Charger

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