MAX745CSLASHD datasheet(6/8 Pages) MAXIM

6 / 8 page

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:

Solving for VADJ, we get:

Set VADJ by choosing a value for R11 (typically 100k),

and determine R3 by:

R3 = [1 - (VADJ / VREF)] x R11 (Figure 1)

where VREF = 4.2V and cell count is 1, 2, 3, or 4

(Table 1).

The voltage-regulation loop is compensated at the CCV

pin. Typically, a series-resistor-capacitor combination

can be used to form a pole-zero doublet. The pole

introduced rolls off the gain starting at low frequencies.

The zero of the doublet provides sufficient AC gain at

mid-frequencies. The output capacitor (C1) rolls off the

mid-frequency gain to below unity. This guarantees sta-

bility before encountering the zero introduced by the

C1’s equivalent series resistance (ESR). The GMV

amplifier’s output is internally clamped to between one-

fourth and three-fourths of the voltage at REF.

Current Control

The charging current is set by a combination of the cur-

rent-sense resistor value and the SETI pin voltage. The

current-sense amplifier measures the voltage across

the current-sense resistor, between CS and BATT. The

current-sense amplifier’s gain is 6. The voltage on SETI

is buffered and then divided by 4. This voltage is com-

pared to the current-sense amplifier’s output.

Therefore, full-scale current is accomplished by con-

necting SETI to REF. The full-scale charging current

(IFS) is set by the following:

IFS = 185mV / R1 (Figure 1)

9.523 V

cell count

9.023V

ADJ

BATT

REF

()

−

= cell count x V

9.523

BATT

REF

ADJ

REF

()

−





















CELL0

CELL1

GND

CELL COUNT

REF

(UP TO 24V)

DCIN

VIN

BST

DHI

DLO

PGND

BATT

THM 1

VADJ

SETI

CCI

47nF

R11

100k

R16

0.1

µF

0.1

µF

M1A

1/2 IRF7303

M1B

MBRS

340T3

MBRS

340T3

0.2

Ω

µF

µH

1/2 IRF7303

IN4148

R12

R15

10k

0.1

µF

4.7

µF

C2, 0.1µF

10k

GND

IBAT

CCV

MAX745

BATTERY

THM/SHDN

STATUS

Figure 1. Standard Application Circuit

Table 1. Cell-Count Programming Table

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