UC1842/3/4/5
UC2842/3/4/5
OUTPUT SATURATION CHARACTERISTICS
ERROR AMPLIFIER OPEN-LOOP
FREQUENCY RESPONSE
OPEN-LOOP LABORATORY FIXTURE
High peak currents associated with capacitive loads ne-
cessitate careful grounding techniques. Timing and by-
pass capacitors should be connected close to pin 5 in a
single point ground. The transistor and 5k potentiometer
are used to sample the oscillator waveform and apply
an adjustable ramp to pin 3.
SHUT DOWN TECHNIQUES
Shutdown of the UC1842 can be accomplished by two
methods; either raise pin 3 above 1V or pull pin 1 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 domi-
nant so that the output will remain low until the next
6
clock cycle after the shutdown condition at pin 1 and/or
3 is removed. In one example, an externally latched
shutdown may be accomplished by adding an SCR
which will be reset by cycling V
CC
below the lower
UVLO threshold. At this point the reference turns off, al-
lowing the SCR to reset.
TI [ TEXAS INSTRUMENTS ]
