TL284x, TL384x

CURRENT-MODE PWM CONTROLLERS

SLVS038E – JANUARY 1989 – REVISED DECEMBER 1999

11

POST OFFICE BOX 655303

APPLICATION INFORMATION

shutdown technique

The PWM controller (see Figure 7) can be shut down by two methods: either raise the voltage at ISENSE above

1 V or pull the COMP terminal below a voltage two diode drops above ground. Either method causes the output

of the PWM comparator to be high (refer to block diagram). The PWM latch is reset dominant so that the output

remains low until the next clock cycle after the shutdown condition at the COMP or ISENSE terminal is removed.

In one example, an externally latched shutdown can be accomplished by adding an SCR that resets by cycling

330

Ω

1 k

Ω

500

Ω

To Current-Sense

Resistor

REF

ISENSE

Shutdown

Shutdown

COMP

Figure 7. Shutdown Techniques

A fraction of the oscillator ramp can be resistively summed with the current-sense signal to provide slope

compensation for converters requiring duty cycles over 50% (see Figure 8). Note that capacitor C forms a filter

with R2 to suppress the leading-edge switch spikes.

RT

0.1

µF

CT

R1

R2

ISENSE

RSENSE

C

REF

RT/CT

ISENSE

Figure 8. Slope Compensation