APPLICATION NOTE

by R. LIOU

A Li-Ion BATTERY CHARGER USING TSM102A

This application note explains how to use the

TSM102 in an SMPS-type battery charger which

features :

.

Voltage Control

.

Current Control

.

Low Battery Detection and End Of Charge

Detection

1 - TSM102 PRESENTATION

The TSM102 integrated circuit includes two Opera-

tional Amplifiers, two Comparators and one adjust-

able precision Voltage Reference (2.5V to 36V,

0.4% or 1%).

TSM102 can sustain up to 36V power supply volt-

age.

1

2

3

14

15

16

5

6

7

12

11

10

V

CC

+

Vref

Ca tho de

V

CC

-

COMP

COMP

TS M102

Figure 1 : TSM102 Pinout

2 - APPLICATION CONTEXT AND PRINCIPLE

OF OPERATION

In the battery charging field which requires ever

increasing performances in more and more re-

duced space, the TSM102A provides an attractive

solution in terms of PCB area saving, precision and

versatility.

Figure 2 shows the secondary side of a battery

charger (SMPS type) where TSM102A is used in

optimised conditions : the two Operational Amplifi-

ers perform current and voltage control, the two

Comparators provide ”End of Charge” and ”Low

Battery” signals and the Voltage Reference en-

sures precise reference for all measurements.

The TSM102A is supplied by an auxiliary power

supply (forward configuration - D7) regulated by a

bipolar transistor and a zener diode on its base (Q2

and DZ), and smoothed by the capacitors C3 and

C4. R15 polarizes the base of the transistor and at

the same time limits the current through the zener

diode during regulation mode of the auxiliary power

supply.

The current and voltage regulations are made

thanks to the two Operational Amplifiers.

The first amplifier senses the current flow through

the sense resistor Rs and compares it with a part

of the reference voltage (resistor bridge R7, R8,

R9). The second amplifier compares the reference

voltage with a part of the charger’s output (resistor

bridge R1, R2, R3).

When either of these two operational amplifiers

tends to lower its ouput, this linear information is

propagated towards the primary side via two ORing

diodes (D1, D2) and an optocoupler (D3). The

compensation loops of these regulation functions

are ensured by the capacitors C1 and C2.

TSM102

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