TD230D datasheet(12/15 Pages) STMICROELECTRONICS

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TD230

S hutdown

Vcc +

Figure 10 :

Visual Alarm-Shutdown

Rs e ns e

TD230

Figure 11 : Step Up Noise Reduction

where CISS1/2 ,CSS1/2,VTH1/2 ,IP/N1 are respectively

the input capacitance, the soft start capacitor, the

threshold voltage and the internal gate current

sources of NMOS1/2 ; and where VSP1/2 ,CTRIP1/2 ,

IP/N2 are respectively the voltage source, current

source and external capacitor of the protection

mode pins PM1/2. Considering the typical values of

VSP1/2,IP/N2,IP/N1, and the fact that classical power

MOSFETs have a threshold voltage around 5V, this

condition can be translated to inequation (vi) :

• CTRIP1/2 > 0.8 x (CSS1/2 +CISS )(vi)

If CISS = 1nF and CSS1/2 = 4.7nF, CTRIP1/2 should

be superior to 4.56nF.

Table (b) summerizes Protection Mode Time Con-

stants corresponding to different CTRIP1/2 values.

Table (b) : Protection Mode Time Constants

CTRIP1/2

Time Constant Range

for Protection Mode

- Shutdown -

22nF

#10ms

220nF

#100ms

2.2

µF

#1s

µF

#10s

5. ENHANCEMENTS

The performances of TD230 are well adapted to

most of the circuit breaking applications in many

differents industry segments (Telecom, Automo-

tive, Industrial, Computer etc...), but in the case of

very demanding environment, or outstanding fea-

tures, the few following advices may be helpful.

5.1. Step-Up Noise Reduction

The inductive step-up converter inevitably gener-

ates current peaks in the output of the power switch

which, in most cases are, are not worrying. But in

some very demanding applications, it is necessary

to remove this noise.

A good way to eliminate such peaks is to add a

resistor connected in series with the inductance

and an electrolytic capacitor between the common

point of resistor and inductance, and ground of the

Step-Up Converter as shown on figure 11.

The resistor’s voltage drop will be due to the prod-

uct of the average consumption current with the

resistor’s value and the inductive current peaks will

be totally absorbed by the capacitor. With a 100

Ω

resistor, the voltage drop is negligible and the

attenuationgood with a 4.7

µF as shown on

figure 12.

Figure 12 : Step Up Noise Reduction

TD230

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