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750mA Output Drive, Source or Sink
8 to 35V Operation
Transmits Drive Logic and Power
through Low Cost Transformer
Programmable Operating Frequency
Up to 750kHz Operation
Improved Output Control Algorithm
Minimizes Output Jitter
Fault Logic Monitors Isolated High
Side IGBT Driver UC1727 for Faults
User Programmable Fault Timing
Screens False Fault Signals
Shutdown Mode Disables On Chip
Logic Reference for Low Standby
Power
Optional External Biasing of Logic
Circuitry can Reduce Overall Power
Dissipation
DESCRIPTION
The UC1726 Isolated Drive Transmitter, and its companion chip, the
UC1727 Isolated High Side IGBT Driver, provide a unique solution to driv-
ing isolated power IGBTs. They are particularly suited to drive the high
side devices on a high voltage H-bridge. The UC1726 device transmits
the drive logic and drive power, along with transferring and receiving fault
information with the isolated gate circuit using a low cost pulse trans-
former.
This drive system utilizes a duty cycle modulation technique that gives in-
stantaneous response to the drive control transitions, and reliably passes
steady state, or DC conditions. High frequency operation, up to 750kHz,
allows the cost and size of the coupling transformer to be minimized.
The UC1726 can be powered from a single V
CC
supply which internally
generates a voltage reference for the logic circuitry. It can also be placed
into a low power shutdown mode that disables the internal reference. The
IC鈥檚 logic circuitry can be powered from an external supply, V
L
, to mini-
mize overall power dissipation. Fault logic monitors the Isolated High Side
IGBT Driver UC1727 for faults. Based on user defined timing, the
UC1726 distinguishes valid faults, which it responds to by setting the fault
latch pin. This also disables the gate drive information until the fault reset
pin is toggled to a logic one.
The UC1726 operates over an 8 to 35 volt supply range. The typical V
CC
voltage will be greater than 28 volts to be compatible with the UC1727.
The undervoltage lockout circuitry of the Isolated High Side IGBT Driver
UC1727 locks out the drive information during its undervoltage lockout.
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BLOCK DIAGRAM
UDG-94004-1
7/95
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