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, NCV384xBV
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 UC384xBV, NCV384xBV = +105°C for UC3844BV, UC3845BV
=+125°C for NCV384xBV
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
