Datasheet

UCC27323, UCC27324, UCC27325
UCC37323, UCC37324, UCC37325
SLUS492H –JUNE 2001–REVISED MAY 2013 www.ti.com
APPLICATION INFORMATION
General Information
High-frequency power supplies often require high-speed, high-current drivers such as the UCC37323/4/5 family.
A leading application is the needed to provide a high-power buffer stage between the PWM output of the control
IC and the gates of the primary power MOSFET or IGBT switching devices. In other cases, the driver IC is used
to drive the power-device gates through a drive transformer. Synchronous rectification supplies are also needed
to simultaneously drive multiple devices which presents an extremely large load to the control circuitry.
Driver ICs are used when having the primary PWM regulator IC directly drive the switching devices for one or
more reasons is not feasible. The PWMIC does not have the brute drive capability required for the intended
switching MOSFET, limiting the switching performance in the application. In other cases there may be a desire to
minimize the effect of high-frequency switching noise by placing the high current driver physically close to the
load. Also, newer ICs that target the highest operating frequencies do not incorporate onboard gate drivers at all.
Their PWM outputs are only intended to drive the high impedance input to a driver such as the UCC37323/4/5.
Finally, the control IC is under thermal stress due to power dissipation, and an external driver helps by moving
the heat from the controller to an external package.
Input Stage
The input thresholds have a 3.3-V logic sensitivity over the full range of V
DD
voltage; yet it is equally compatible
with 0 V to V
DD
signals.
The inputs of UCC37323/4/5 family of drivers are designed to withstand 500-mA reverse current without either
damage to the IC for logic upset. The input stage of each driver must be driven by a signal with a short rise or fall
time. This condition is satisfied in typical power-supply applications, where the input signals are provided by a
PWM controller or logic gates with fast transition times (<200 ns). The input stages to the drivers function as a
digital gate, and are not intended for applications where a slow-changing input voltage is used to generate a
switching output when the logic threshold of the input section is reached. While this may not be harmful to the
driver, the output of the driver may switch repeatedly at a high frequency.
Users must not attempt to shape the input signals to the driver in an attempt to slow down (or delay) the signal at
the output. If limiting the rise or fall times to the power device is desired, limit the rise or fall times to the power
device, then add an external resistance between the output of the driver and the load device, which is generally a
power MOSFET gate. The external resistor also helps remove power dissipation from the IC package, as
discussed in the section on Thermal Considerations (see THERMAL INFORMATION).
Output Stage
Inverting outputs of the UCC37323 and OUTA of the UCC37325 are intended to drive external P-channel
MOSFETs. Noninverting outputs of the UCC37324 and OUTB of the UCC37325 are intended to drive external N-
channel MOSFETs.
Each output stage is capable of supplying ±4-A peak current pulses and swings to both VDD and GND. The
pullup and pulldown circuits of the driver are constructed of bipolar and MOSFET transistors in parallel. The peak
output current rating is the combined current from the bipolar and MOSFET transistors. The output resistance is
the R
DS(on)
of the MOSFET transistor when the voltage on the driver output is less than the saturation voltage of
the bipolar transistor. Each output stage also provides a very low impedance to overshoot and undershoot due to
the body diode of the internal MOSFET. In many cases, external-schottky-clamp diodes are not required.
The UCC37323 family delivers 4-A of gate drive where it is most needed during the MOSFET switching
transition — at the Miller plateau region — providing improved efficiency gains. A unique BiPolar and MOSFET
hybrid output stage in parallel also allows efficient current sourcing at low supply voltages.
6 Submit Documentation Feedback Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: UCC27323 UCC27324 UCC27325 UCC37323 UCC37324 UCC37325