TL5001, TL5001A

PULSE-WIDTH-MODULATION CONTROL CIRCUITS

SLVS084E – APRIL 1994 – REVISED OCTOBER 1999

4

POST OFFICE BOX 655303

dead-time control (DTC) (continued)

R

DT +

Rt ) 1250 D Voscmax – Voscmin ) Voscmin

Where

soft start, the voltage at DTC is derived by the following equation:

V

DT [

I

DT

R

DT

1–e

–t R

DT

C

DT

TL5001/A

DTC

CDT

RDT

6

Figure 2. Soft-Start Circuit

every time UVLO or SCP becomes active.

undervoltage-lockout (UVLO) protection

The undervoltage-lockout circuit turns the output transistor off and resets the SCP latch whenever the supply

voltage drops too low (approximately 3 V at 25

°C) for proper operation. A hysteresis voltage of 200 mV

eliminates false triggering on noise and chattering.

short-circuit protection (SCP)

The TL5001/A includes short-circuit protection (see Figure 3), which turns the power switch off to prevent

damage when the converter output is shorted. When activated, the SCP prevents the switch from being turned

on until the internal latching circuit is reset. The circuit is reset by reducing the input voltage until UVLO becomes

active or until the SCP terminal is pulled to ground externally.

When a short circuit occurs, the error-amplifier output at COMP rises to increase the power-switch duty cycle

in an attempt to maintain the output voltage. SCP comparator 1 starts an RC timing circuit when COMP exceeds

1.5 V. If the short is removed and the error-amplifier output drops below 1.5 V before time out, normal converter

operation continues. If the fault is still present at the end of the time-out period, the timer sets the latching circuit

and turns off the TL5001/A output transistor.