TSM111

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AN EXAMPLE OF 90W MICRO ATX POWER

SUPPLY USING L5991A, VIPER20 AND

TSM111

Protection against accidental short circuits and

fault conditions is mandatory in PC power sup-

plies. These protection circuits can be realized by

using many discrete components which occupy a

lot of PCB space, design time in fine tuning the cir-

cuit and also add to assembling costs.

ST’s single chip TSM111 IC provides complete

protection circuits design easier, with fewer num-

ber of components. TSM111 is an ideal supervisor

IC for PC power supplies.

The salient features and benefits of this device are

listed below :

a) Over voltage protection for 3.3V, 5V and 12V

without external component.

b) Over current protection for 3.3V, 5V and 12V.

c) Generates Power Good signal.

d) Programmable timing for Power Good signal.

e) Wide range supply operating voltage up to 36V

(44V AMR).

f) Stable internal voltage reference.

g) Two 1.6% voltage reference for Main and Aux-

iliary regulation.

h) Few external components.

i) Circuit occupies little space on PCB.

j) Easy implementation of the circuit.

FEATURE DESCRIPTIONS

a) Over voltage protection can be implemented

without any additional components. Overvoltage

sense levels for 3.3V, 5V, 12V are 4V, 6.1V, 14.2V

respectively. With very little tolerances, better pro-

tection is achieved.

b) Over current protection can be implemented

with very small value sense resistors. As the cur-

rent sense threshold levels are set very low, regu-

lation is not affected. The current sense threshold

levels for 3.3V, 5V, 12V are 50mV, 50mV and

65mV respectively.

c) The power good signal (pin9) is asserted to in-

dicate the 5V and 3.3V is above the under voltage

threshold level. PG pin goes high when the above

condition is reached. Pull up resistor R27 (3.1K) is

connected to 5V STDBY supply from this pin.

d) The timing of the power good signal can be con-

trolled by adjusting the value of the charging ca-

pacitor on pin 10. With 2.2

µF/16V capacitor on pin

10, 400msec turn on delay is achieved.

e) The power supply can be operated from 14.5V

to 36V. The VCC must always be higher than the

supply voltage on the 12V input pin by 2V .i.e. if

14V is appearing 12V input pin the Vcc must be >

16V.

f) Two internal high precision TL431 shunt regula-

tors are built-in. It provides stable reference volt-

ages with a voltage precision of 1.6%.