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