TSM101/A
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If pin 2 is connected to ground, the internal current
source is enabled, the current measurement is
off-setted by a voltage equal to :
• Vr4 = Io x R4 with Io = 1.4mA
This can be used to lower the charging current or
eventually to stop the charge, if V
r4
> V
r5
In our example, the current offset is equal to 700 -
200mA = 500mA, representing a voltage offset
Vr4 = 140mV across R4.
The following values are used on the application
board :
• R5 = 4 *1.2Ω 0.5W in parallel
• R4 = 100Ω
• R2 = 1.2kΩ
• R3 = 220Ω
• R9 = short circuit
• R1 = 10kΩ
• C2 = 100nF
• C5 = 100nF
• C1 = output capacitor of the SMPS
• C4 = 10µF
4 - SCHEMATIC DIAGRAM
Figure 2 represents a schematic of the output cir-
cuit of a “classical” SMPS using a TL431 for volt-
age regulation. This circuit is modified to use
theTSM101 and the final circuit is represented in
figure 3.
Figure 3 : SMPS Using the TSM101
5 - IMPROVEMENT
5.1. High frequency compensation
Two R-C devices (R9 + C2 & R10 + C3) are used
to stabilize the regulation at high frequencies.
The calculation of these values is not easy and is
a function of the transfer function of the SMPS.
A guess value for the capacitors C2 and C3 is
100nF.
5.2. Power supply for TSM101
In applications requiring low voltage battery
charge or when the charger is in current regulation
mode, the output voltage can be too low to supply
correctly the TSM101.
The same problem occurs when the output is
short-circuited.
A solution to provide a quasi constant supply volt-
age to the TSM101 is shown at figure 4 : an auxil-
iary winding is added at the secondary side of the
transformer.
This winding is forward coupled to the primary
winding, the voltage across it is directly propor-
tional to the mains rectified voltage, even if the fly-
back voltage is close to zero.
As this auxiliary winding is a voltage source, it is
necessary to add a resistor (R11) on the cathode
of the rectifier (D3) to limit the current.
A low cost regulator (Q2 and Zener diode D4) is
used to power the TSM101. This is necessary with
autoranging SMPS with wide input voltages, for
example 90 to 240V without switching. In standard
SMPS with voltage range from 200 to 240VAC or
100 to 130VAC, this regulator can be removed
and replaced by the small power supply shown on
figure 5 (Raux, Caux, D2).
