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INSTRUMENTS
SM72482
www.ti.com
SNVS696C –JANUARY 2011–REVISED APRIL 2013
DETAILED OPERATING DESCRIPTION
The SM72482 dual gate driver consists of two independent and identical driver channels with TTL compatible
logic inputs and high current totem-pole outputs that source or sink current to drive MOSFET gates. The driver
output consist of a compound structure with MOS and bipolar transistor operating in parallel to optimize current
capability over a wide output voltage and operating temperature range. The bipolar device provides high peak
current at the critical threshold region of the MOSFET VGS while the MOS devices provide rail-to-rail output
swing. The totem pole output drives the MOSFET gate between the gate drive supply voltage VCC and the power
ground potential at the VEE pin.
The control inputs of the drivers are high impedance CMOS buffers with TTL compatible threshold voltages. The
SM72482 pinout was designed for compatibility with industry standard gate drivers in single supply gate driver
applications.
The input stage of each driver should be driven by a signal with a short rise and fall time. Slow rising and falling
input signals, although not harmful to the driver, may result in the output switching repeatedly at a high
frequency.
The two driver channels of the SM72482 are designed as identical cells. Transistor matching inherent to
integrated circuit manufacturing ensures that the AC and DC peformance of the channels are nearly identical.
Closely matched propagation delays allow the dual driver to be operated as a single with inputs and output pins
connected. The drive current capability in parallel operation is precisely 2X the drive of an individual channel.
Small differences in switching speed between the driver channels will produce a transient current (shoot-through)
in the output stage when two output pins are connected to drive a single load. Differences in input thresholds
between the driver channels will also produce a transient current (shoot-through) in the output stage. Fast
transition input signals are especially important while operating in a parallel configuration. The efficiency loss for
parallel operation has been characterized at various loads, supply voltages and operating frequencies. The
power dissipation in the SM72482 increases less than 1% relative to the dual driver configuration when operated
as a single driver with inputs/ outputs connected.
An Under Voltage Lock Out (UVLO) circuit is included in the SM72482, which senses the voltage difference
between VCC and the chip ground pin, VEE. When the VCC to VEE voltage difference falls below 2.8V both driver
channels are disabled. The UVLO hysteresis prevents chattering during brown-out conditions and the driver will
resume normal operation when the VCC to VEE differential voltage exceeds approximately 3.0V.
The SM72482MY –1 device hold both outputs in the low state in the under-voltage lockout (UVLO) condition. The
SM72482MA–4 has an active high output state of OUT_A during UVLO. When VCC is less than the UVLO
threshold voltage, OUT_A will be locked in the high state while OUT_B will be disabled in the low state. This
configuration allows the SM72482MY –4 to drive a PFET through OUT_A and an NFET through OUT_B with
both FETs safely turned off during UVLO.
Layout Considerations
Attention must be given to board layout when using SM72482. Some important considerations include:
1. A Low ESR/ESL capacitor must be connected close to the IC and between the VCC and VEE pins to support
high peak currents being drawn from VCC during turn-on of the MOSFET.
2. Proper grounding is crucial. The drivers need a very low impedance path for current return to ground
avoiding inductive loops. The two paths for returning current to ground are a) between SM72482 VEE pin and
the ground of the circuit that controls the driver inputs, b) between SM72482 VEE pin and the source of the
power MOSFET being driven. All these paths should be as short as possible to reduce inductance and be as
wide as possible to reduce resistance. All these ground paths should be kept distinctly separate to avoid
coupling between the high current output paths and the logic signals that drive the SM72482. A good method
is to dedicate one copper plane in a multi-layered PCB to provide a common ground surface.
3. With the rise and fall times in the range of 10 ns to 30 ns, care is required to minimize the lengths of current
carrying conductors to reduce their inductance and EMI from the high di/dt transients generated by the
SM72482.
4. The SM72482 footprint is compatible with other industry standard drivers including the TC4426/27/28 and
UCC27323/4/5.
5. If either channel is not being used, the respective input pin (IN_A or IN_B) should be connected to either VEE
or VCC to avoid spurious output signals.
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