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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
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