UCC1800/1/2/3/4/5
UCC2800/1/2/3/4/5
UCC3800/1/2/3/4/5
The UCC3800/1/2/3/4/5 oscillator generates a sawtooth
waveform on RC. The rise time is set by the time constant
of RT and CT. The fall time is set by CT and an internal tran-
sistor on-resistance of approximately 125 . During the fall
time, the output is off and the maximum duty cycle is re-
duced below 50% or 100% depending on the part number.
Larger timing capacitors increase the discharge time and re-
duce the maximum duty cycle and frequency.
Figure 1. Oscillator.
Figure 2. Error amplifier gain/phase response.
4.00
3.98
3.96
3.94
3.92
3.90
3.88
3.86
3.84
3.82
1000
100
10
10
100
(k )
1000
4
4.2 4.4 4.6 4.8
5
5.2 5.4 5.6 5.8
6
R
T
V
CC (V)
Figure 3. UCC1803/5 VREF vs. VCC; ILOAD = 0.5mA.
Figure 4. UCC1800/1/2/4 oscillator frequency vs. RT and
CT.
6
ROCHESTER [ Rochester Electronics ]
