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TSM1121: Housekeeping IC.

TSM1121 is a one chip solution for all PC SMPS:

it integrates on one chip the Housekeeping

Circuitry

(Over

Voltage

and

Under

Voltage

protections, with adequate sequencing).

Triple Power Line Protection

The TSM1121 Housekeeping Circuit is dedicated

to 3.3V, 5V and 12V power lines protection. It

integrates a Precision Voltage Reference, a Triple

Over Voltage Protection Circuit and a Triple

Under Voltage Protection Circuit as well as all the

necessary logic and transient timing management

circuits for optimal and secure communication

with the motherboard, during start up, switch off

and stabilized conditions.

Over Voltage Protection

The Over Voltage Protection Circuit is made of

three comparators with internal voltage thresholds

(Vov33, Vov5, Vov12) which do not require any

external components for proper operation. The

outputs of these three comparators are ORed.

Under Voltage Protection

The Under Voltage Protection Circuit is made of

three comparators with internal voltage thresholds

(Vuv33, Vuv5, Vuv12) which do not require any

external components for proper operation. The

outputs of these three comparators are ORed,

and blanked by an internal delay circuitry (Power

Up Blanking - Tuv) which can be adjusted with an

external capacitor (Cuv). This allows that during

power up, the under voltage protection circuit is

inhibited.

Latch OFF

The Over Voltage and Under Voltage Circuits

outputs are again ORed before activating a latch.

When activated, this latch commands the full

switch OFF of the three main power lines (3.3V,

5V, 12V) by an external link between the

housekeeping and the primary PWM circuits via

the main optocoupler or any other device . Note

that the Under Voltage Circuit, after Power Up UV

blanking, bears no other delay to the latch setting

input whereas the Over Voltage circuit bears an

additional Tfault delay time. This allows an

efficient protection against Output Short Circuit

conditions.

Power Good

The Over Voltage and Under Voltage Circuits are

Ored to switch the Power Good output active (PG)

to warn the motherboard that the voltage of at

least one of the three power lines is out of range.

The PG activation bears an internal Tpg delay

circuitry which can be adjusted with an external

capacitor (Cpg).

Remote Control

Thanks to this information link to the motherboard,

a resetting signal to the latch is achievable with

the Remote pin (REM). When the Remote pin is

active,

the

external

Fault

link

between

Housekeeping circuit and the PWM generator is

active (high = PWM OFF) and the PG pin is active

(high). Note that to reset effectively the latch, a

minimum width Remote pulse should be applied

thanks to an internal delay circuitry (Trem) which

can be adjusted with an external capacitor

(Crem).

TSM1121

Principle of Operation and Application Hints