TPIC44H01DA datasheet(21/28 Pages) TI

21 / 28 page

TPIC44H01

4-CHANNEL SERIAL AND PARALLEL HIGH-SIDE PRE-FET DRIVER

SLIS088 – SEPTEMBER 1998

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

dynamic over-current threshold generation

Figure 13 shows the internal circuitry associated with V(PK_x) and the external resistor divider and capacitor

connected to V(COMPx). The intent of this implementation is to allow a dynamicV(COMPx) voltage to be generated

which begins at the voltage referenced to the V(PK_x) pin and decays as an RC discharge to the resistor divider

voltage setup by the network on the V(COMPx) pin. Figure 14 shows an example of the dynamic V(COMPx) voltage

waveform. This waveform will be generated each time a channel is switched from off to on by either a serial bit

or parallel input. The V(OVDS) threshold begins at a high value to allow the high in-rush current associated with

cold lamp filament resistance and decays at an RC time constant to emulate the current decrease in the lamp

as the filament warms up. The steady-state threshold after the RC decay provides protection against soft-short

conditions that could cause the FET to over heat after a long period of time. Selection of V(PK_x) voltage and

V(COMPx) resistor divider and capacitor provides the user with the flexibility to accommodate a wide variety of

lamp types. The TPIC44H01 thus provides a wide dynamic range of the over-current detection function, and

a time-dependent variation in the threshold that are user adjustable by the selection of external components.

1.5

0.5

–20

100

2.5

t – Time – ms

140

180

220

120

160

200

240

Dynamic V(COMPx),

V(peak) = 2.5 V,

V(sustained) = 0.2 V

Figure 14. Dynamic Fault Threshold Voltage

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