UC3845A High Performance
Current Mode Controller
The UC3845A series of high performance
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.
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.
The UC3845A is designedfor lower voltage
applications having UVLO thresholds of 8.5V (on)
and 7.6V (off).
Also included are protective features
consisting of input and reference undervoltage lockouts
each with hysteresis, cycle–by–cycle current limiting,
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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
CDSUFFIX
PLASTIC PACKAGE
8 DIP
D8SUFFIX
PLASTIC PACKAGE
8 SOP
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
CSSUFFIX
PLASTIC PACKAGE
SOP-14
SIMPLIFIEDBLOCKDIAGRAM
PINCONNECTIONS
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 VCC 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
Tlow = 0°C, Thigh = +70°C.
4. This parameter is measured at the latch trip point with VFB = 0V.
∆V Output Compensation
∆V Current Sense Input
5. Comparator gain is defined as: AV
4-30