AS384x
Current Mode Controller
SEMICONDUCTOR
Features
Description
2.5 V bandgap reference trimmed to
The AS3842 family of control ICs provide pin-for-pin replacement of the
industry standard UC3842 series of devices. The devices are
redesigned to provide significantly improved tolerances in power sup-
ply manufacturing. The 2.5 V reference has been trimmed to 1.0%
tolerance. The oscillator discharge current is trimmed to provide guar-
anteed duty cycle clamping rather than specified discharge current.
The circuit is more completely specified to guarantee all parameters
impacting power supply manufacturing tolerances.
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1.0% and temperature-compensated
Standard temperature range extended
to 105¡C
AS3842/3 oscillations trimmed for
precision duty cycle clamp
AS3844/5 have exact 50% max duty
cycle clamp
In addition, the oscillator and flip-flop sections have been enhanced to
provide additional performance. The RT/CT pin now doubles as a syn-
chronization input that can be easily driven from open collector/open
drain logic outputs. This sync input is a high impedance input and can
easily be used for externally clocked systems. The new flip-flop topol-
ogy allows the duty cycle on the AS3844/5 to be guaranteed between
49 and 50%. The AS3843/5 requires less than 0.5 mA of start-up cur-
rent over the full temperature range.
Advanced oscillator design simplifies
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synchronization
Improved specs on UVLO and
hysteresis provide more predictable
start-up and shutdown
Improved 5 V regulator provides better
AC noise immunity
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Guaranteed performance with current
sense pulled below ground
Pin Configuration Ñ Top view
PDIP (N)
8L SOIC (D8)
14L SOIC (D14)
COMP
V
COMP
V
COMP
NC
V
REG
1
2
3
4
8
7
6
5
1
2
3
4
8
7
6
5
1
2
3
4
5
6
7
14
13
12
11
10
9
REG
REG
V
V
V
V
CC
NC
FB
CC
FB
ISENSE
RT/CT
OUT
GND
ISENSE
RT/CT
OUT
GND
V
V
FB
CC
NC
ISENSE
NC
V
C
OUT
PWR G
GND
8
RT/CT
Ordering Information
AS384X D8 13
Circuit Type:
Packaging Option:
Current Mode Controller (See Table A)
= Tube
T
= Tape and Reel (13" Reel Dia)
13
Package Style
Table A
D8 = 8 Pin Plastic SOIC
D14 =14 Pin Plastic SOIC
N = 8 Pin Plastic DIP
Duty Cycle
Typ.
Model
AS3842
AS3843
AS3844
AS3845
VCC(min)
VCC(on)
16
8.4
16
8.4
ICC
10
7.6
10
97%
97%
49.5%
49.5%
0.5 mA
0.3 mA
0.5 mA
0.3 mA
7.6
ASTEC Semiconductor
1