(1)Compatible with Voltage or Current Mode Topologies (2)50ns Propagation Delay to Output
(3)Practical Operation Switching Frequencies to 1MHz (4)High Current Dual Totem Pole Outputs (1.5A Peak)
(5)Wide Bandwidth Error Amplifier (6)Fully Latched Logic with Double Pulse Suppression
(7)Pulse-by-Pulse Current Limiting (8)Soft Start / Max. Duty Cycle Control
(9)Under-Voltage Lockout with Hysteresis (10)Low Start Up Current (1.1mA)
DESCRIPTION
The UC1825 family of PWM control ICs is optimized for high frequency switched mode power supply applications. Particular care was given to minimizing propagation delays through the comparators 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 with a 1V threshold, a TTL compatible shutdown port, and a soft start pin which will double as a maximum duty cycle clamp. The logic is fully latched to provide jitter free operation and prohibit multiple pulses at an output. An under-voltage lockout section with 800mV of hysteresis assures low start up current. During under-voltage lockout, the out-puts are high impedance.
These devices feature totem pole outputs designed to source and sink high peak currents from capacitive loads, such as the gate of a power MOSFET. The on state is designed as a high level.
Printed Circuit Board Layout Considerations
High speed circuits demand careful attention to layout and component placement. To assure proper performance of the UC1825 follow these rules: 1) Use a ground plane. 2) Damp or clamp parasitic inductive kick energy from the gate of driven MOSFETs. Do not allow the out-put pins to ring below ground. A series gate resistor or a shunt 1 Amp Schottky diode at the output pin will serve.
| Package | QJA | QJC |
| DIL-16J | 80-120 | 28(2) |
| DIL-16N | 90(1) | 45 |
| PLCC-20 | 43-75(1) | 34 |
| LCC-20 | 70-80 | 20(2) |
| SOIC-16 | 50-120(1) | 35 |
