UC3844, UC3845, UC2844, UC2845
ELECTRICAL CHARACTERISTICS (V = 15 V, (Note 4), R = 10 k, C = 3.3 nF, T = T to T
(Note 5), unless otherwise noted.)
CC
T
T
A
low
high
UC284X
Typ
UC384X
Characteristics
ERROR AMPLIFIER SECTION (continued)
Unity Gain Bandwidth (T = 25°C)
Symbol
Min
Max
Min
Typ
Max
Unit
BW
0.7
60
1.0
70
−
−
0.7
60
1.0
70
−
−
MHz
dB
J
Power Supply Rejection Ratio (V = 12 V to 25 V)
PSRR
CC
Output Current
mA
Sink (V = 1.1 V, V = 2.7 V)
2.0
−0.5
12
−1.0
−
−
2.0
−0.5
12
−1.0
−
−
I
O
FB
Sink
Source (V = 5.0 V, V = 2.3 V)
O
FB
I
Source
Output Voltage Swing
V
High State (R = 15 k to ground, V = 2.3 V)
5.0
−
6.2
0.8
−
1.1
5.0
−
6.2
0.8
−
1.1
V
V
L
FB
OH
Low State (R = 15 k to V , V = 2.7 V)
L
ref
FB
OL
CURRENT SENSE SECTION
Current Sense Input Voltage Gain (Notes 6 & 7)
Maximum Current Sense Input Threshold (Note 6)
Power Supply Rejection Ratio
A
2.85
0.9
3.0
1.0
3.15
1.1
2.85
0.9
3.0
1.0
3.15
1.1
V/V
V
V
V
th
PSRR
dB
V
= 12 V to 25 V (Note 6)
−
−
−
70
−
−
−
−
70
−
CC
Input Bias Current
I
−2.0
150
−10
300
−2.0
150
−10
300
mA
IB
Propagation Delay (Current Sense Input to Output)
t
ns
PLH(IN/OUT)
OUTPUT SECTION
Output Voltage
V
Low State (I
= 20 mA)
= 200 mA)
= 20 mA)
= 200 mA)
−
−
12
12
0.1
1.6
13.5
13.4
0.4
2.2
−
−
−
13
12
0.1
1.6
13.5
13.4
0.4
2.2
−
V
Sink
Sink
Sink
Sink
OL
(I
High State (I
(I
V
OH
−
−
Output Voltage with UVLO Activated
= 6.0 V, I = 1.0 mA
V
OL(UVLO)
V
V
CC
−
−
−
0.1
50
50
1.1
150
150
−
−
−
0.1
50
50
1.1
150
150
Sink
Output Voltage Rise Time (C = 1.0 nF, T = 25°C)
t
r
ns
ns
L
J
Output Voltage Fall Time (C = 1.0 nF, T = 25°C)
t
f
L
J
UNDERVOLTAGE LOCKOUT SECTION
Startup Threshold
UCX844
UCX845
V
V
V
th
15
7.8
16
8.4
17
9.0
14.5
7.8
16
8.4
17.5
9.0
Minimum Operating Voltage After Turn−On
V
CC(min)
UCX844
UCX845
9.0
7.0
10
7.6
11
8.2
8.5
7.0
10
7.6
11.5
8.2
PWM SECTION
Duty Cycle
Maximum
Minimum
%
46
−
48
−
50
0
47
−
48
−
50
0
DC
DC
max
min
TOTAL DEVICE
Power Supply Current (Note 4)
Startup:
I
mA
V
CC
(V = 6.5 V for UCX845A,
−
−
0.5
12
1.0
17
−
−
0.5
12
1.0
17
CC
(V 14 V for UCX844) Operating
CC
Power Supply Zener Voltage (I = 25 mA)
V
30
36
−
30
36
−
CC
Z
4. Adjust V above the Startup threshold before setting to 15 V.
CC
5. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
T
= 0°C for UC3844, UC3845
−25°C for UC2844, UC2845
T
= +70°C for UC3844, UC3845
+85°C for UC2844, UC2845
low
high
6. This parameter is measured at the latch trip point with V = 0 V.
FB
DV Output Compensation
7. Comparator gain is defined as: A
V
DV Current Sense Input
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