TSM101AI datasheet(7/15 Pages) STMICROELECTRONICS

7 / 15 page

The current regulation is effective when the voltage

drop across R5 is equal to the voltage on pin 5 of

the TSM101 (assuming that the internal current

source is disabled).

For medium currents (<1A), a voltage drop across

R5 of 200mV = Vr5 is a good value, R5 can be

realized with standard low cost 0.5W resistors in

parallel.

• R5 =

Vr5

Ich

, R5 = 0.285

Ω (four 1.2Ω resistor in

parallel)

R2 and R3 can be chosen using the following

formula :

• R2 = R3 x (

Vref

− Vr5)

Vr5

CHARGE CONTROL

If the pin 2 is left open, the charge current is nominal

at # 700mA.

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 Vr4 >Vr5

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

circuit of a ”classical” SMPS using a TL431 for

voltage regulation. This circuit is modified to use

the TSM101 and the final circuit is represented in

figure 3.

Figure 3 : SMPS Using the TSM101

TSM101/A

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