UC3877

Features:

• Zero to 100% Duty Cycle Control
• Programmable Output Turn-On Delay
• Compatible with Voltage or Current Mode Topologies
• Practical Operation at Switching Frequencies to 1MHz
• Four 2A Totem Pole Outputs
• 10MHz Error Amplifier
• Undervoltage Lockout
• Low Startup Current 150A
• Outputs Active Low During UVLO
• Soft-Start Control
• Latched Over-Current Comparator With Full Cycle Restart
• Trimmed Reference


Pinout




Specifications

Supply Voltage (VC, VIN)     . . . . . . . . . . . . . . . . . . . . . . . . . . 20V
Output Current, Source or Sink
    DC    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5A
    Pulse (0.5s)   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3A
Analog I/0s
    (Pins 1, 2, 3, 4, 5, 6, 7, 15, 16, 17, 18, 19)   . . . . 0.3 to 5.3V
Storage Temperature Range . . . . . . . . . . . . . 65°C to +150
Junction Temperature. . . . . . . . . . . . . . . . . . . 55°C to +150 
Lead Temperature (Soldering, 10 sec.)     . . . . . . . . . . . . +300 


Note: Pin references are to 20 pin packages. All voltages are with respect to ground. Currents are positive into, negative out of, device terminals. Consult Unitrode databook for information regarding thermal specifications and limitations of packages.


Description

The UC3877 integrated circuits implements control of a bridge power stage by phase-shifting the switching of one half-bridge with respect to the other, allowing constant frequency pulse-width modulation in combination with resonant, zero-voltage switching for high efficiency performance at high frequencies. This UC3877 circuits may be configured to provide control in either voltage or current mode operation, with a separate over-current shutdown for fast fault protection.

A programmable time delay of UC3877 is provided to insert a dead-time at the turn-on of each output stage. This delay, providing time to allow the resonant switching action, is independently controllable for each output pair (A-B, C-D).

With the oscillator UC3877 capable of operation at frequencies in excess of 2MHz, overall switching frequencies to 1MHz are practical. In addition to the standard free running mode, with the CLOCKSYNC pin, the user may configure these devices to accept an external clock synchronization signal, or may lock together up to 5 units with the operational frequency determined by the fastest device.

Protective features of UC3877 include an undervoltage lockout which maintains all outputs in an active-low state until the supply reaches a 10.75V threshold. 1.5V hysteresis is built in for reliable, boot-strapped chip supply. Over-current protection is provided, and will latch the outputs in the OFF state within 70nsec of a fault. The current-fault circuitry of UC3877 implements full-cycle restart operation.

Additional features of UC3877 include an error amplifier with bandwidth in excess of 7MHz, a 5V reference, provisions for soft-starting, and flexible ramp generation and slope compensation circuitry.

These UC3877 are available in 20-pin DIP, 28-pin "bat-wing" SOIC and 28 lead power PLCC plastic packages for operation over both 0°C to 70°C and 25°C to +85°C temperature ranges; and in hermetically sealed cerdip, and surface mount packages for 55°C to +125°C operation.