UC3844B, UC3845B, UC2844B, UC2845B
http://onsemi.com
4
ELECTRICAL CHARACTERISTICS (V
CC
= 15 V [Note 11], R
T
= 10 k, C
T
= 3.3 nF. For typical values T
A
= 25°C, for min/max
values T
A
is the operating ambient temperature range that applies [Note 12], unless otherwise noted.)
UC284XB UC384XB, XBV
Characteristic Symbol Min Typ Max Min Typ Max Unit
PWM SECTION
Duty Cycle
Maximum (UC284XB, UC384XB)
Maximum (UC384XBV)
Minimum
DC
(max)
DC
(min)
47
−
−
48
−
−
50
−
0
47
46
−
48
48
−
50
50
0
%
TOTAL DEVICE
Power Supply Current
Startup (V
CC
= 6.5 V for UCX845B,
Startup (V
CC
= 14 V for UCX844B, BV)
Operating (Note 11)
I
CC
−
−
0.3
12
0.5
17
−
−
0.3
12
0.5
17
mA
Power Supply Zener Voltage (I
CC
= 25 mA) V
Z
30 36 − 30 36 − V
11. Adjust V
CC
above the Startup threshold before setting to 15 V.
12.Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
T
low
=0°C for UC3844B, UC3845B T
high
=+70°C for UC3844B, UC3845B
= − 25°C for UC2844B, UC2845B = + 85°C for UC2844B, UC2845B
= − 40°C for UC3844BV, UC3845BV = +105°C for UC3844BV, UC3845BV
0.8
2.0
5.0
8.0
20
50
80
R
T
, TIMING RESISTOR (k )
Ω
1.0 M500 k200 k100 k50 k20 k10 k
f
OSC
, OSCILLATOR FREQUENCY (kHz)
Figure 2. Timing Resistor
versus Oscillator Frequency
Figure 3. Output Deadtime
versus Oscillator Frequency
1.0 M100 k10 k
f
OSC
, OSCILLATOR FREQUENCY (kHz)
50
% DT, PERCENT OUTPUT DEADTIME
1.C
T
= 10 nF
2.C
T
= 5.0 nF
3.C
T
= 2.0 nF
4.C
T
= 1.0 nF
5.C
T
= 500 pF
6.C
T
= 200 pF
7.C
T
= 100 pF
55
60
65
70
75
20 k 50 k 200 k 500 k
2
3
7
5
6
NOTE: Output switches at
1/2 the oscillator frequency
V
CC
= 15 V
T
A
= 25°C
0.5 ms/DIV
20 mV/DIV
2.55 V
2.5 V
2.45 V
V
CC
= 15 V
A
V
= -1.0
T
A
= 25°C
V
CC
= 15 V
A
V
= -1.0
T
A
= 25°C
1.0 ms/DIV
200 mV/DIV
2.5 V
3.0 V
2.0 V
Figure 4. Error Amp Small Signal
Transient Response
Figure 5. Error Amp Large Signal
Transient Response
1
4
For R
T
u 5KfX
1.72
R
T
C
T