TSM111 datasheet(14/18 Pages) STMICROELECTRONICS

14 / 18 page

TSM111 is a Housekeeping IC which is best used

in PC Switch Mode Power Supplies for secondary

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

TSM111 integrates all the necessary functions for a

secure and reliable overcurrent and overvoltage

protection, as well as a logic interface for proper

communication with the motherboard and adjust-

able timing circuitry for optimized sequencing man-

agement. Moreover, TSM111 integrates two pre-

cise shunt voltage references for direct optocoupler

drive. TSM111, integrating the equivalent of more

than 25 discrete components, saves a lot of design

time and fine tuning, as well as PCB area, and in-

creases the reliability of the whole application.

How to use the TSM111 Evaluation Board ?

This evaluation board allows to adapt the TSM111

housekeepingchip to an already existing PC Power

Supply by simply choosing proper values for it’s ex-

ternal components, and making the adequate con-

nections to the I/O of the evaluation board.

The Electrical Schematic of the TSM111 evaluation

board is shown on figure 1. It includes the TSM111

as well as the minimum component number re-

quired to make the TSM111 fit in a PC SMPS appli-

cation.

Components calculations

The overvoltage protection is not to be adjusted. In-

ternal voltage thresholds are given by Vvs1, Vvs2,

Vvs3 for respective protection of the 3.3V, 5V, 12V

power lines.

The overcurrent protection is given by the choice of

the Sense resistors R1, R2, R3 (respectively for

eachpower line 3.3V, 5V, 12V). Internalprecise volt-

age thresholds define the tripping voltage drops for

each line following equations 1, 2 & 3 :

Vcs1 = R1 x I33

eq1

Vcs2 = R2 x I5

eq2

Vcs3 = R3 x I12

eq3

where I33, I5, and I12 are the tripping currents.

The system will latch (Fault output will be active -

high) if the overcurrent lasts more than the author-

ized surge delay Tsur given by equations 4 & 5 :

Icharge = Vcc / R4

eq4

Tsur = (C1 x Vsur) / Icharge

eq5

Note that eq4 is an approximation of a capacitive

charge where Vcc (16V min) is large versus the

threshold voltage Vsur (2.5V).

R4=33k

Ω, C1=4.7µF => Tsur=21ms

Thanks to the Tsur adjustment, the normal surge

currents which occur during power up (capacitive

EVALUATION BOARD - TECHNICAL NOTICE

Vs 3 3

Is 3 3

Is 5

Vs 5

Is 1 2

Vs 1 2

Vr e f M a i n

Fb m a i n

Vr e f Au x

Fb A u x

Tpor

Rem

TR e m

Ad j

Gn d

Vc c

Tsur

PWM

TSM111

rs3.3V

rs5V

rs12V

Rsur

Csur

Crem

R5 R rem

Cpor

Vdet

Fault

Optaux

In3.3V

Vdet

Optaux

Fault

In5V

In12V

Out12V

Out5V

Out3.3V

Out12V

Out5V

J10

Out3.3V

J11

SW1

BP Rem

J12

Rem

Fro m c

5Vstby

J13

Vcc

J14

Gnd

VCC

J15

VrefMain

RoptMain

VrefAux

Roptaux

J16

VrefAux

R10

J20

1INV

J18

OptMain

Vin

GN D

Vout

U2 78L05

5Vstby

R11

5Vstby

In5V

IN12V

EVALUATION BOARD - ELECTRICAL SCHEMATIC

TSM111

14/18

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