KA35S280/281

Lead-Acid Battery Charger

2011 Nov 18

© 2011

8

- Pulsed-current charge

This algorithm consists of three phases (figure 6):

1.

Pending is annunciated by LED0 and LED3 flashing.

2.

3.

Phase3 - Maintenance: Charging current is removed until the battery voltage falls to

V

BLK

V

FLT

V

TH

Time

I

MAX

I

COND

I

MIN

I

FLT

Phase 1

Phase 2

Phase 3

Fast Charge

Maintenance

Voltage

Current

Figure 6

– Fast Charge

- Temperature monitoring

- Temperature compensation

The KA35S28X senses temperature by monitoring the voltage of TEMP pin. The KA35S28X

assumes a Negative Temperature Coefficient (NTC) thermistor, so the voltage on the TEMP

pin is inversely proportional to the temperature (see Figure 7). The temperature thresholds

used by the KA35S28X and their corresponding TEMP pin voltage are:

TCO Temperature Cut-Off: Higher limit of the temperature range in which charging is

HTF

High-Temperature Fault: Threshold to which temperature must drop after

LTF

Low-Temperature Fault: Lower limit of the temperature range in which charging is

A resistor-divider network must be implemented that presents the defined voltage levels to

the TEMP pin at the desired temperatures (see Figure 8). The equations for determining

Equation 1:

Equation 2:

Where:

1% resistors are recommended. As an example, the resistor values for several temperature

windows computed for a

3KΩ thermistor are shown in Table 7.