UC1823
UC2823
UC3823
High Speed PWM Controller
FEATURES
DESCRIPTION
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Compatible with Voltage or Current-Mode
Topologies
The UC1823 family of PWM control ICs is optimized for high fre-
quency switched mode power supply applications. Particular care
was given to minimizing propagation delays through the compara-
tors and logic circuitry while maximizing bandwidth and slew rate
of the error amplifier. This controller is designed for use in either
current-mode or voltage-mode systems with the capability for input
voltage feed-forward.
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Practical Operation @ Switching
Frequencies to 1.0MHz
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50ns Propagation Delay to Output
High Current Totem Pole Output (1.5A peak)
Wide Bandwidth Error Amplifier
Protection circuitry includes a current limit comparator, a TTL com-
patible shutdown port, and a soft start pin which will double as a
maximum duty cycle clamp. The logic is fully latched to provide jit-
ter free operation and prohibit multiple pulses at the output. An un-
der-voltage lockout section with 800mV of hysteresis assures low
start up current. During under-voltage lockout, the output is high im-
pedance. The current limit reference (pin 11) is a DC input voltage to
the current limit comparator. Consult specifications for details.
Fully Latched Logic with Double Pulse
Suppression
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Pulse-by-Pulse Current Limiting
Soft Start/Max. Duty Cycle Control
Under-Voltage Lockout with Hysteresis
Low Start Up Current (1.1mA)
These devices feature a totem pole output designed to source and
sink high peak currents from capacitive loads, such as the gate of
a power MOSFET. The on state is defined as a high level.
Trimmed Bandgap Reference (5.1V ±1%)
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (Pins 15, 13) . . . . . . . . . . . . . . . . . . . . . . . . 30V Oscillator Charging Current (Pin 5) . . . . . . . . . . . . . . . . . . -5mA
Output Current, Source or Sink (Pin14) Power Dissipation at TA = 60 °C . . . . . . . . . . . . . . . . . . . . . 1W
DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5A Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C
Pulse (0.5µs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0A Lead Temperature (Soldering, 10 seconds) . . . . . . . . . . 300°C
Analog Inputs (Pins 1, 2, 7, 8, 9, 11) . . . . . . . . . . . -0.3V to +6V Note: All voltages are with respect to ground, Pin 10.
Currents are positive into the specified terminal.
Consult Packaging Section of Databook for thermal
limitations and considerations of packages.
Clock Output Current (Pin 4) . . . . . . . . . . . . . . . . . . . . . . . -5mA
Error Amplifier Output Current (Pin 3) . . . . . . . . . . . . . . . . 5mA
Soft Start Sink Current (Pin 8) . . . . . . . . . . . . . . . . . . . . . 20mA
BLOCK DIAGRAM
3/97
1