TSM121

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1.5. Output Driver - Open Collectors

The typical driving current from the TSM121 is

25mA. The recommended values of R12 to R16

are:

R12=R13=3.9k

Ω, R14=R15=7.5kΩ, R16=2kΩ

2. Housekeeping Circuit

The TSM121 Housekeeping Circuit is dedicated to

3.3V, 5V, and 12V power lines protection. It inte-

grates a Precision Voltage reference (indepen-

dent from the PWM generator circuit Voltage Ref-

erence), a triple Over current Protection circuit, 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.

2.1. Over current protection circuit

The Over current protection circuit is made of 3

comparators with internal voltage thresholds re-

quiring 3 different Sense resistors in series with

the 3 different power lines. The thresholds are in-

ternally fixed to the Vcs33, Vcs5, Vcs12 values,

and the sense resistors need to be chosen de-

pending on the required over current limit. The

outputs of these three comparators are ORed, and

blanked by an internal delay circuitry (Surge Cur-

rent Blanking - Tsur) which can be adjusted with

external components (Rsur, Csur). Note that the

three Over current protection circuits are blanked

from current surges by the same delay circuit. This

allows that during power up, large inrush currents

are allowed during a short period of time corre-

sponding to the charging of capacitive loads (see

figure 3).

The maximum output currents of the 12V, 5V, and

3.3V lines are determined by Rs12, Rs5 and Rs33

respectively:

I12max = Vcs12 / Rs12

I5max = Vcs5 / Rs5

I33max = Vcs33 / Rs33

2.2. Over voltage protection circuit

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.

2.3. Under voltage protection circuit

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

UV Blanking - Tuv) which can be adjusted with ex-

ternal components (Cuv). This allows that during

power up, the under voltage protection circuit is in-

hibited.

2.4. Logic Interface

The Over current, 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 internal link between the

Housekeeping and the PWM circuits. Note that

the Under voltage circuit, after power up UV blank-

ing, bears no other delay to the Latch setting input

whereas the Over current and Over voltage cir-

cuits both bear an additional Tfault delay time.

This allows an efficient protection against Output

Short Circuit Conditions.

The Over current, Over voltage and Under voltage

circuits are all ORed to switch the Power Good

output active (PG) to warn the motherboard that

the voltage of at least one of the three power line

is out of range. The PG activation bears an inter-

nal Tpg delay circuitry which can be adjusted with

external components (Cpg)

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 internal Fault link between Housekeep-

ing circuit and the PWM generator is active (high:

PWM off), the PG pin is active (high). Note that to

reset effectively the Latch, a minimum width Re-

mote pulse should be applied thanks to an internal

delay circuitry (Trem) which can be adjusted with

external components (Crem).

2.5. Additional circuits:

A Power Input (PI) is available for a supplementa-

ry power condition supervision. For example, the

supervision of the Vcc power supply line.

An Extra Protection (EP) circuit is available for an

additional input power protection. For example,

this operator can be used for the supervision of

the primary input power via an additional wiring at

the foot of the power half bridge. This operator can

also be used for the supervision of eventual nega-

tive power lines (ex: -5V or -12V).