5

UC2909

UC3909

GND: The reference point for the internal reference, all

thresholds, and the return for the remainder of the de-

vice. The output sink transistor is wired directly to this

pin.

OVCTAP: The overcharge current taper pin detects

when the output current has tapered to the float thresh-

old in the overcharge state.

to ground. The ramp oscillates between approximately

1.0V to 3.0V and the frequency is approximated by:

frequency

CR

TSET

=

••

1

12

.

OUT: The output of the PWM driver which consists of an

open collector output transistor with 100mA sink capabil-

ity.

R10: Input used to establish a differential voltage corre-

sponding to the temperature of the thermistor. Connect

a 10k resistor to ground from this point.

RSET:

A resistor to ground programs the oscillator

charge current and the trickle control current for the oscil-

lator ramp.

The oscillator charge current is approximately

175

.

.

mately

0115

.

.

RTHM: A 10k thermistor is connected to ground and is

thermally connected to the battery. The resistance will

vary exponentially over temperature and its change is

used to vary the internal 2.3V reference by –3.9mV/°C.

The recommended thermistor for this function is part

number L1005-5744-103-D1, Keystone Carbon Com-

pany, St. Marys, PA.

STAT0:

This open collector pin is the first decode bit

used to decode the charge states.

STAT1: This open collector pin is the second decode bit

used to decode the charge states.

STATLV: This bit is high when the charger is in the float

state.

VA–: The inverting input to the voltage error amplifier.

VAO: The output of the voltage error amplifier. The up-

per output clamp voltage of this amplifier is 5V.

VCC: The input voltage to the chip. The chip is opera-

tional between 7.5V and 40V and should be bypassed

with a 1

shown in Figure 1.

VLOGIC: The precision reference voltage. It should be

bypassed with a 0.1

µF capacitor.

Charge State Decode Chart

STAT0 and STAT1 are open collector outputs. The out-

put is approximately 0.2V for a logic 0.

STAT1

STAT0

Trickle Charge

0

0

Bulk Charge

0

1

Over Charge

1

0

Float Charge

1

1

PIN DESCRIPTIONS (cont.)