UC3844A High Performance
Current Mode Controller
The UC3844A series of high performance
fixed frequency current mode controllers are
specifically designed for off–line and dc–to–dc
converter applications offering the designer a cost
effective solution with minimal external components.
This integrated circuit features an oscillator, a
temperature compensated reference, high gain error
amplifier, current sensing comparator, and a high
current totem pole output ideally suited for driving a
power MOSFET.
Also included are protective features
consisting of input and reference undervoltage lockouts
each with hysteresis, cycle–by–cycle current limiting,
a latch for single pulse metering, and a flip-flop which
blanks the output off every other oscillator cycle,
allowing output deadtimes to be programmed for 50%
to 70%.
This device is available in an 8–pin dual–in–
line plastic package as well as the 14–pin plastic sur-
face mount (SOP–14). The SOP–14 package has sepa-
rate power and ground pins for the totem pole output
stage.
The UC3844A has UVLO thresholds of
16V (on) and 10V (off), Ideally suited for off-line
converters.
l
l
l
l
l
l
l
l
Output Deadtime Adjustable from 50% to 70%
Current Mode Operation to 500 kHz
Automatic Feed Forward Compensation
Latching PWM for Cycle–By–Cycle Current Limiting
Internally Trimmed Reference with Undervoltage Lockout
High Current Totem Pole Output
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
CD SUFFIX
PLASTIC PACKAGE
8 DIP
D8 SUFFIX
PLASTIC PACKAGE
8 SOP
CS SUFFIX
PLASTIC PACKAGE
SOP-14
SIMPLIFIED BLOCK DIAGRAM
PIN CONNECTIONS
Pin numbers adjacent to terminals are for the D suffix 8-DIP package.
Pin numbers in parenthesis are for the S suffix SOP–14 package.
NOTES:
1. Maximum Package power dissipation limits must be observed.
2. Adjust V
CC
above the Startup threshold before setting to 15 V.
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible
T
low
= 0°C, T
high
= +70°C.
4. This parameter is measured at the latch trip point with V
FB
= 0V.
5. Comparator gain is defined as: A
V
∆V
Output Compensation
∆V
Current Sense Input
4-24
FCI [ FIRST COMPONENTS INTERNATIONAL ]
