KA35S280 View Datasheet(PDF) - Kasin Electronics Corporation

Part Name

Description

Manufacturer

KA35S280

Lead-Acid Battery Charger

Kasin Electronics Corporation 

KA35S280/281

Lead-Acid Battery Charger

IMAX Fast charge current specified as a function of “C,” the capacity of the battery in

Ampere-hours (e.g., a charge rate of 1C for a 5Ah battery is 5A). Typical values

range from C/10 to C, although some battery vendors may approve higher

charge rates.

The KA35S28X monitors battery pack voltage at the VBAT pin. A voltage divider between the

positive and negative terminals of the battery pack is used to present a scaled battery pack

voltage to the VBAT pin. The KA35S28X also uses the voltage across a sense resistor (RSNS)

between the negative terminal of the battery pack and ground to monitor current. See

Figure 3 and below equations for the configuration of this network.

Equation 1:

And IMAX is determined by:

Equation 2:

Where:

N = Number of series cells in the battery pack

IMAX = Desired maximum charge current

V BAT

I BAT

KA35S28X

BAT+

RB 1

RB 2

BAT-

R SNS

Figure 3 - Configuring the Battery Divider

The KA35S28X internal band-gap reference voltage at 25°C is 2.2V. This reference shifts

with temperature at -3.9mV/°C to compensate for the negative temperature coefficient of

lead-acid chemistry.

The total resistance presented by the divider between BAT+ and BAT- (RB1 + RB2) should

be between 100KΩ and 1MΩ. The minimum value ensures that the divider network does

not drain the battery excessively when the power source is disconnected. Exceeding the

maximum value increases the noise susceptibility of the VBAT pin. 1% resistors are

recommended.

Table 6 shows the several examples of resistor selections.

Table 6 – RB1, RB2 Values by Number of Cells and RSNS by Desired IMAX

N

3 (6V)

6 (12V)

12 (24V)

RB1 (KΩ)

57KΩ

147KΩ

327KΩ

RB2 (KΩ)

33KΩ

33KΩ

33KΩ

IMAX

0.5

1A

1.5A

RSNS (Ω)

0.4Ω

0.2Ω

0.13Ω

2011 Nov 18

© 2011 Kasin Technology Inc.

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