UC3844B, UC3845B, UC2844B, UC2845B
ELECTRICAL CHARACTERISTICS
(V
CC
= 15 V [Note 8], 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 9], unless otherwise noted.)
UC284XB
Characteristic
PWM SECTION
Duty Cycle
Maximum (UC284XB, UC384XB)
Maximum
(UC384XBV)
Minimum
TOTAL DEVICE
Power Supply Current
Startup (V
CC
= 6.5 V for UCX845B,
Startup (V
CC
=
14 V for UCX844B, BV)
Operating (Note 8)
Power Supply Zener Voltage (I
CC
= 25 mA)
I
CC
−
−
V
Z
30
0.3
12
36
0.5
17
−
−
−
30
0.3
12
36
0.5
17
−
V
mA
%
DC
(max)
DC
(min)
47
−
−
48
−
−
50
−
0
47
46
−
48
48
−
50
50
0
Symbol
Min
Typ
Max
UC384XB, XBV
Min
Typ
Max
Unit
8. Adjust V
CC
above the Startup threshold before setting to 15 V.
9. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
T
high
= + 70°C for UC3844B, UC3845B
T
low
= 0°C for UC3844B, UC3845B
= − 25°C for UC2844B, UC2845B
= + 85°C for UC2844B, UC2845B
= − 40°C for UC3844BV, UC3845BV
= +105°C for UC3844BV, UC3845BV
80
50
R T, TIMING RESISTOR (k
Ω
)
20
8.0
5.0
2.0
0.8
10 k
NOTE: Output switches at
1/2 the oscillator frequency
20 k
% DT, PERCENT OUTPUT DEADTIME
V
CC
= 15 V
T
A
= 25°C
75
70
65
60
55
50 k
100 k
200 k
500 k
f
OSC
, OSCILLATOR FREQUENCY (kHz)
1.0 M
50
10 k
Figure 2. Timing Resistor
versus Oscillator Frequency
2.55 V
V
CC
= 15 V
A
V
= −1.0
T
A
= 25°C
3.0 V
20 mV/DIV
2.5 V
2.5 V
2.45 V
0.5
ms/DIV
2.0 V
1.0
ms/DIV
Figure 4. Error Amp Small Signal
Transient Response
Figure 5. Error Amp Large Signal
Transient Response
http://onsemi.com
5
200 mV/DIV
ÄÄÄÄÄ
ÄÄÄÄÄ
ÄÄÄÄÄ
ÄÄÄÄÄ
ÄÄÄÄÄ
1.
2.
3.
4.
5.
6.
7.
C
T
= 10 nF
C
T
= 5.0 nF
C
T
= 2.0 nF
C
T
= 1.0 nF
C
T
= 500 pF
C
T
= 200 pF
C
T
= 100 pF
20 k
3
2
1
4
7
5
6
50 k 100 k
200 k
500 k
f
OSC
, OSCILLATOR FREQUENCY (kHz)
1.0 M
Figure 3. Output Deadtime
versus Oscillator Frequency
V
CC
= 15 V
A
V
= −1.0
T
A
= 25°C
ONSEMI [ ON SEMICONDUCTOR ]
