frequency =

1

¾

1.2 ·

·

C

R

T

SET

1.75

¾

R

SET

0.115

¾

R

SET

UC2909-EP

www.ti.com

SLUSA72 – JULY 2010

DEVICE INFORMATION

TERMINAL FUNCTIONS

TERMINAL

DESCRIPTION

NAME

NO.

CA-

13

The inverting input to the current error amplifier.

The output of the current error amplifier which is internally clamped to approximately 4 V. It is internally

CAO

14

connected to the inverting input of the PWM comparator.

The inverting and non-inverting inputs to the current sense amplifier. This amplifier has a fixed gain of five

CS-, CS+

17, 16

and a common-mode voltage range of from –250 mV to VCC.

CSO

15

The output of the current sense amplifier which is internally clamped to approximately 5.7 V.

The input to a comparator that detects when battery voltage is low and places the charger in a trickle charge

CHGENB

10

state. The charge enable comparator makes the output of the voltage error amplifier a high impedance while

forcing a fixed 10 mA into CA- to set the trickle charge current.

The reference point for the internal reference, all thresholds, and the return for the remainder of the device.

GND

3

The output sink transistor is wired directly to this pin.

The overcharge current taper pin detects when the output current has tapered to the float threshold in the

OVCTAP

9

overcharge state.

The oscillator ramp pin which has a capacitor (CT) to ground. The ramp oscillates between approximately

1 V to 3 V and the frequency is approximated by:

OSC

19

(1)

The output of the PWM driver which consists of an open collector output transistor with 100-mA sink

OUT

5

capability.

Input used to establish a differential voltage corresponding to the temperature of the thermistor. Connect a

R10

20

10-K

Ω resistor to ground from this point.

A resistor to ground programs the oscillator charge current and the trickle control current for the oscillator

ramp.

The oscillator charge current is approximately:

RSET

18

(2)

The trickle control current (ITRCK_CONTROL) is approximately:

(3)

A 10-K

Ω 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 2.3-V reference by -3.9

RTHM

1

mV/°C. The recommended thermistor for this function is part number L1005-5744-103-D1, Keystone Carbon

Company, St. Marys, PA.

STAT0

7

This open collector pin is the first decode bit used to decode the charge states.

STAT1

6

This open collector pin is the second decode bit used to decode the charge states.

STATLV

8

This bit is high when the charger is in the float state.

VA-

12

The inverting input to the voltage error amplifier.

VAO

11

The output of the voltage error amplifier. The upper output clamp voltage of this amplifier is 5 V.

The input voltage to the chip. The chip is operational between 7.5 V and 40 V and should be bypassed with

VCC

4

a 1-µF capacitor. A typical ICC vs. temperature is shown in Figure 1.

VLOGIC

2

The precision reference voltage. It should be bypassed with a 0.1-µF capacitor.

Copyright © 2010, Texas Instruments Incorporated

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