
C
U R R E N T
M
O D E
PWM C
O N T R O L L E R
UC184xA/284xA/384xA
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
Copyright 1995
Rev. 1.2 12/95
4
P
R O D U C T I O N
D
A T A
S
H E E T
E L E C T R I C A L C H A R A C T E R I S T I C S
(Con't.)
Under-Voltage Lockout Section
Start Threshold
Parameter
Symbol
Test Conditions
x842A/4A
x843A/5A
x842A/4A
x843A/5A
Min. Operation Voltage After Turn-On
UC384xA
Units
Min. Typ. Max. Min. Typ. Max.
UC184xA/284xA
15
7.8
9
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
11.5
8.2
V
V
V
V
PWM Section
Maximum Duty Cycle
x842A/3A
x844A/5A
Minimum Duty Cycle
Total Standby Section
Start-Up Current
Operating Supply Current
Zener Voltage
94
47
96
48
100
50
0
94
47
96
48
100
50
0
%
%
%
I
CC
V
Z
I
CC
= 25mA
0.3
11
35
0.5
17
0.3
11
35
0.5
17
mA
mA
V
30
30
B L O C K D I A G R A M
*- V
and V
are internally connected for 8 pin packages.
**- POWER GROUND and GROUND are internally connected for 8 pin packages.
***- Toggle flip flop used only in x844A and x845A series.
Notes: 2. These parameters, although guaranteed, are not 100% tested in
production.
3. Parameter measured at trip point of latch with V
VFB
= 0.
V
COMP
V
ISENSE
4. Gain defined as: A
VOL
=
; 0
≤
V
ISENSE
≤
0.8V.
5. Adjust V
above the start threshold before setting at 15V.
6. Output frequency equals oscillator frequency for the UC1842A
and UC1843A. Output frequency is one half oscillator frequency
for the UC1844A and UC1845A.
7. "Temperature stability, sometimes referred to as average temperature
coefficient, is described by the equation:
V
REF
(max.) - V
REF
(min.)
T
J
(max.) - T
J
(min.)
Temp Stability =
V
(max.) & V
(min.) are the maximum & minimum reference
voltage measured over the appropriate temperature range. Note that
the extremes in voltage do not necessarily occur at the extremes in
temperature."
UVLO
S / R
5V
Ref
Internal
Bias
34V
Error Amp
1V
Current Sense
Comparator
PWM
Latch
S
R
R
Oscillator
2R
**
T
***
V
Good Logic
2.5V
UVLO
16V (1842A/4A)
8.4V (1843A/5A)
Hysteresis
6V (1842A/4A)
0.8V (1843A/5A)
COMP
CURRENT SENSE
V
FB
R
T
/C
T
GROUND
*
V
CC
V
5.0V
50mA
V
C
*
OUTPUT
POWER GROUND**