AS2842/3/4/5
Current Mode Controller
Description
The AS2842 family of control ICs provide pin-for-pin replace-
ment of the industry standard UC3842 series of devices. The
devices are redesigned to provide significantly improved
tolerances in power supply manufacturing. The 2.5 V refer-
ence has been trimmed to 1.0% tolerance. The oscillator
discharge current is trimmed to provide guaranteed duty
cycle clamping rather than specified discharge current. The
circuit is more completely specified to guarantee all param-
eters impacting power supply manufacturing tolerances.
In addition, the oscillator and flip-flop sections have been
enhanced to provide additional performance. The R
T
/C
T
pin
now doubles as a synchronization 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 topology
allows the duty cycle on the AS2844/5 to be guaranteed
between 49 and 50%. The AS2843/5 requires less than
0.5 mA of start-up current over the full temperature range.
Pin Configuration — Top view
Features
•
2.5 V bandgap reference
trimmed to 1.0% and
temperature-compensated
•
Extended temperature range
from - 40 to 105° C
•
AS2842/3 oscillations trimmed
for precision duty cycle clamp
•
AS2844/5 have exact 50% max
duty cycle clamp
•
Advanced oscillator design
simplifies synchronization
•
Improved specs on UVLO
and hysteresis provide
more predictable start-up
and shutdown
•
Improved 5 V regulator provides
better AC noise immunity
•
Guaranteed performance
with current sense pulled
below ground
•
Over-temperature shutdown
8L SOIC (D)
81COMP V
REG
72V
FB
V
CC
63I
SENSE
OUT
54R
T
/C
T
GND
PDIP (N)
81COMP V
REG
72V
FB
V
CC
63I
SENSE
OUT
54R
T
/C
T
GND
Ordering Information
Description Temperature Range Order Codes
8-Pin Plastic DIP -40 to 105° C AS2842/3/4/5N
8-Pin Plastic SOIC -40 to 105° C AS2842/3/4/5D-8
ASTEC Semiconductor
37