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IR3551 Datasheet(PDF) 17 Page - International Rectifier
IRF [International Rectifier]
IR3551 Datasheet(HTML) 17 Page - International Rectifier
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July 16, 2013 | DATASHEET V3.2
50A Integrated PowIRstage®
12) Determine the case temperature with VCC = 5V, which
is +4.0° based on the dashed lines in Figure 13.
13) Determine the case temperature with L=210nH, which
is -1.4° based on the dashed lines in Figure 14.
14) Sum the case temperature adjustment from 9) to 13),
-0.9° -1.8° -02° +4.0° -1.4° = -0.3°. Add the delta to the
required ambient temperature in step 8), 45°C + (-
0.3°C) = 44.7°C, at which the maximum current is
temperature is 125°C, as shown in Figure 9. If only
105°C junction temperature is allowed, the required
ambient temperature is equivalent to 44.7°C + (125°C -
105°C) = 64.7°C, which indicates 37A maximum
current at the 45°C required ambient temperature.
INDUCTOR CURRENT SENSING CAPACITOR C
AND RESISTOR R
If the IR3551 is used with inductor DCR sensing, care must
be taken in the printed circuit board layout to make a
Kelvin connection across the inductor DCR. The DC
resistance of the inductor is utilized to sense the inductor
current. Usually the resistor R
and capacitor C
with the inductor are chosen to match the time constant of
the inductor, and therefore the voltage across the
represents the inductor current.
Measure the inductance L and the inductor DC resistance
. Pre-select the capacitor C
and calculate R
INPUT CAPACITORS C
At least two 10uF 1206 ceramic capacitors and one 0.22uF
0402 ceramic capacitor are recommended for decoupling
the VIN to PGND connection. The 0.22uF 0402 capacitor
should be on the same side of the PCB as the IR3551 and
next to the VIN and PGND pins. Adding additional
capacitance and use of capacitors with lower ESR and
mounted with low inductance routing will improve
efficiency and reduce overall system noise, especially in
single-phase designs or during high current operation.
BOOTSTRAP CAPACITOR C
A minimum of 0.22uF 0402 capacitor is required for the
bootstrap circuit. A high temperature 0.22uF or greater
value 0402 capacitor is recommended. It should be
mounted on the same side of the PCB as the IR3551 and as
close as possible to the BOOST pin. A low-inductance PCB
routing of the SW pin connection to the other terminal of
the bootstrap capacitor is required to minimize the ringing
between the BOOST and SW pins.
VCC DECOUPLING CAPACITOR C
A 0.22uF to 1uF ceramic decoupling capacitor is required at
the VCC pin. It should be mounted on the same side of the
PCB as the IR3551 and as close as possible to the VCC and
PGND (pin 4). Low inductance routing between the VCC
capacitor and the IR3551 pins is strongly recommended.
BODY-BRAKING® PIN FUNCTION
The BBRK# pin should be pulled up to VCC if the feature is
not used by the PWM controller. Use of a 4.7kΩ resistor or
a direct connection to VCC is recommended.
MOUNTING OF HEAT SINKS
Care should be taken in the mounting of heat sinks so as
not to short-circuit nearby components.
The VCC and
Bootstrap capacitors are typically mounted on the same
side of the PCB as the IR3551. The mounting height of
these capacitors must be considered when selecting their
HIGH OUTPUT VOLTAGE DESIGN
The IR3551 is capable of creating output voltages above
the 3.3V recommended maximum output voltage as there
are no restrictions inside the IR3551 on the duty cycle
applied to the PWM pin. However if the current sense
feature is required, the common mode range of the
current sense amplifier inputs must be considered. A
violation of the current sense input common mode range
may cause unexpected IR3551 behavior. Also the output
current rating of the device will be reduced as the duty
cycle increases. In very high duty cycle applications
sufficient time must be provided for replenishment of the
Bootstrap capacitor for the control MOSFET drive.
Contact International Rectifier for a layout example
suitable for your specific application.
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