AN1284 Datasheet, PDF (1/3 Pages) STMicroelectronics – A Li-Ion BATTERY CHARGER USING TSM102A

AN1284
APPLICATION NOTE
A Li-Ion BATTERY CHARGER USING TSM102A
This application note explains how to use the
TSM102 in an SMPS-type battery charger which
features :
u Voltage Control
u Current Control
u Low Battery Detection and End Of Charg
Detection
by R. LIOU
1 - TSM102 PRESENTATION
The TSM102 integrated circuit includes two Oper-
ational Amplifiers, two Comparators and one ad-
justable precision Voltage Reference (2.5V to
36V, 0.4% or 1%).
TSM102 can sustain up to 36V power supply volt-
age.
Figure 1 : TSM102 Pinout
1
2
3
V _CC+
5
6
7
Vref
TSM102
COMP
COMP
16
15
14
V _CC-
12
11
10
Cathode
2 - APPLICATION CONTEXT AND PRINCIPLE
OF OPERATION
In the battery charging field which requires ever in-
creasing performances in more and more reduced
space, the TSM102A provides an attractive solu-
tion 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
July 2000
zener diode during regulation mode of the auxilia-
ry 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 OR-
ing diodes (D1, D2) and an optocoupler (D3). The
compensation loops of these regulation functions
are ensured by the capacitors C1 and C2.
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