鈥?/div>
Compatible with Voltage or Current-Mode
Topologies
Practical Operation @ Switching
Frequencies to 1.0MHz
50ns Propagation Delay to Output
High Current Totem Pole Output (1.5A peak)
Wide Bandwidth Error Amplifier
Fully Latched Logic with Double Pulse
Suppression
Pulse-by-Pulse Current Limiting
Soft Start/Max. Duty Cycle Control
Under-Voltage Lockout with Hysteresis
Low Start Up Current (1.1mA)
Trimmed Bandgap Reference (5.1V
鹵1%)
DESCRIPTION
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.
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.
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.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (Pins 15, 13) . . . . . . . . . . . . . . . . . . . . . . . . 30V
Output Current, Source or Sink (Pin14)
DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5A
Pulse (0.5碌s). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0A
Analog Inputs (Pins 1, 2, 7, 8, 9, 11) . . . . . . . . . . . -0.3V to +6V
Clock Output Current (Pin 4) . . . . . . . . . . . . . . . . . . . . . . . -5mA
Error Amplifier Output Current (Pin 3) . . . . . . . . . . . . . . . . 5mA
Soft Start Sink Current (Pin 8) . . . . . . . . . . . . . . . . . . . . . 20mA
Oscillator Charging Current (Pin 5) . . . . . . . . . . . . . . . . . . -5mA
Power Dissipation at T
A
= 60 擄C . . . . . . . . . . . . . . . . . . . . . 1W
Storage Temperature Range . . . . . . . . . . . . . . -65擄C to +150擄C
Lead Temperature (Soldering, 10 seconds) . . . . . . . . . . 300擄C
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.
BLOCK DIAGRAM
3/97
1
1
2
3
4
5
6
7
