UC1726
UC2726
UC3726
Isolated Drive Transmitter
DESCRIPTION
FEATURES
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750mA Output Drive, Source or Sink
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.
8 to 35V Operation
Transmits Drive Logic and Power
through Low Cost Transformer
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Programmable Operating Frequency
Up to 750kHz Operation
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.
Improved Output Control Algorithm
Minimizes Output Jitter
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Fault Logic Monitors Isolated High
Side IGBT Driver UC1727 for Faults
The UC1726 can be powered from a single VCC 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’s logic circuitry can be powered from an external supply, VL, 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.
User Programmable Fault Timing
Screens False Fault Signals
Shutdown Mode Disables On Chip
Logic Reference for Low Standby
Power
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Optional External Biasing of Logic
Circuitry can Reduce Overall Power
Dissipation
The UC1726 operates over an 8 to 35 volt supply range. The typical VCC
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.
BLOCK DIAGRAM
UDG-94004-1
7/95
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