TD230 datasheet(8/15 Pages) STMICROELECTRONICS

8 / 15 page

To avoid cumulative charging of the protection

capacitors CTRIP 1/2 in case of successive overcur-

rent conditions, the capacitors CTRIP 1/2 are con-

Figure 3 :

Fault Time Limitation

stantly discharged by another fixed current source

IP/N3 which value is a fourth of IP/N2 (1

µA).

Trace 1 represents the CBOOST Voltage (0 to

5+13,4 = 18,4V)

Trace 2 represents the CTRIP1 Voltage.

The value of the capacitors CTRIP 1/2 should be

chosen in relation with the required protection time

as indicated in equation (iv) :

• CTRIP1/2 =(IP/N2 - IP/N3)x tPROTECT1/2 /VSPN/3(iv)

where tPROTECT 1/2 is the time defined by the user

before a definitive resettable shutdown of MOS-

FET 1/2.

Equation (iv) can be translated to :

• CTRIP 1/2 =tPROTECT 1/2 x3µA / 1.20V (iv)

Note that the positive power supply disjonction

leads to the negative power supply disjonction,

whereas the opposite is not true.

2.3. Step-Up Converter

To ensure proper voltage on the gate of the positive

supply NMOS1 (VGS = 13.4V typ), the TD230 inte-

grates a step-up converter which is to be boosted

with two small low cost external components : an

inductor LBOOST and a capacitor CBOOST, as shown

in figure 4.

Rs e ns e

MOS

Lboos t

C boos t

Se ns e

Step Up

Driver

TD230

Figure 4 :

Step Up Converter External

Components

The principle of this inductive step-up converter is

to pump charges in the tank capacitor CBOOST

following the equation (v) :

Lboos t

Cboos t

TD230

Os c

Re gulation

Figure 5 :

Internal Step Up Schematic

• V(CBOOST)= VCC+ + 13.4V typ (v)

Charges are pumped by means of an oscillator

commanded switch, and stored in the CBOOST tank

capacitor through a diode as shown on figure 5.

Wh en th e vo lt a ge across CBOOST reaches

VCC

++13.4V typ, the oscillator is stopped. This

creates a ripple voltage with an amplitude of 0.2V.

Note that the min and max values of V(CBOOST)

comprised between VCC

+ +10V and VCC+ +15V

already take the ripple voltage into account.

TD230

8/15

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