sm72482myx-1 National Semiconductor Corporation, sm72482myx-1 Datasheet - Page 8

• Manufacturer Part Number: sm72482myx-1
• Description: Solarmagic Dual 5a Compound Gate Driver
• Manufacturer: National Semiconductor Corporation

www.national.com
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 cur-
rent to drive MOSFET gates. The driver output consist of a
compound structure with MOS and bipolar transistor operat-
ing 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 V
ground potential at the V
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 cir-
cuit manufacturing ensures that the AC and DC peformance
of the channels are nearly identical. Closely matched propa-
gation delays allow the dual driver to be operated as a single
with inputs and output pins connected. The drive current ca-
pability in parallel operation is precisely 2X the drive of an
individual channel. Small differences in switching speed be-
tween 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 thresh-
olds between the driver channels will also produce a transient
current (shoot-through) in the output stage. Fast transition in-
put signals are especially important while operating in a par-
allel 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 con-
nected.
An Under Voltage Lock Out (UVLO) circuit is included in the
SM72482, which senses the voltage difference between
V
age difference falls below 2.8V both driver channels are dis-
abled. The UVLO hysteresis prevents chattering during
brown-out conditions and the driver will resume normal oper-
ation when the V
proximately 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.
CC
and the chip ground pin, V
CC
to V
EE
EE
pin.
differential voltage exceeds ap-
EE
. When the V
CC
and the power
CC
to V
EE
volt-
8
Layout Considerations
Attention must be given to board layout when using SM72482.
Some important considerations include:
1.
2.
3.
4.
5.
Thermal Performance
INTRODUCTION
The primary goal of thermal management is to maintain the
integrated circuit (IC) junction temperature (T
ified maximum operating temperature to ensure reliability. It
is essential to estimate the maximum T
worst case operating conditions. The junction temperature is
estimated based on the power dissipated in the IC and the
junction to ambient thermal resistance θ
in the application board and environment. The θ
given constant for the package and depends on the printed
circuit board design and the operating environment.
DRIVE POWER REQUIREMENT CALCULATIONS IN
SM72482
The SM72482 dual low side MOSFET driver is capable of
sourcing/sinking 3A/5A peak currents for short intervals to
drive a MOSFET without exceeding package power dissipa-
tion limits. High peak currents are required to switch the
MOSFET gate very quickly for operation at high frequencies.
A Low ESR/ESL capacitor must be connected close to
the IC and between the V
peak currents being drawn from V
MOSFET.
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 V
of the circuit that controls the driver inputs, b) between
SM72482 V
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.
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.
The SM72482 footprint is compatible with other industry
standard drivers including the TC4426/27/28 and
UCC27323/4/5.
If either channel is not being used, the respective input
pin (IN_A or IN_B) should be connected to either V
V
CC
to avoid spurious output signals.
EE
pin and the source of the power MOSFET
CC
and V
CC
EE
J
EE
JA
of IC components in
during turn-on of the
pins to support high
pin and the ground
for the IC package
J
) below a spec-
JA
is not a
EE
or