IR3553_15 datasheet(17/22 Pages) IRF

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July 16, 2014 | DATASHEET V3.3

IR3553

40A Integrated PowIRstage®

12) Determine the case temperature with VCC = 5V, which

is +5.4° based on the dashed lines in Figure 13.

13) Determine the case temperature with L=210nH, which

is -1.8° based on the dashed lines in Figure 14.

14) Sum the case temperature adjustment from 9) to 13),

+0.6° -3.0° -0.4° +5.4° -1.8° = +0.8°. Add the delta to

the required ambient temperature in step 8), 45°C +

(+0.8°C) = 45.8°C, at which the maximum current is

reduced

34A

when

the

allowed

junction

temperature is 125°C, as shown in Figure 9. If only

105°C junction temperature is allowed, the required

ambient temperature is equivalent to 45.8°C + (125°C -

105°C) = 65.8°C, which indicates 29.5A maximum

current at the 45°C required ambient temperature.

INDUCTOR CURRENT SENSING CAPACITOR CCS

AND RESISTOR RCS

If the IR3553 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 RCS and capacitor CCS in parallel

with the inductor are chosen to match the time constant of

the inductor, and therefore the voltage across the

capacitor CCS represents the inductor current.

Measure the inductance L and the inductor DC resistance

RL. Pre-select the capacitor CCS and calculate RCS as follows.



INPUT CAPACITORS CVIN

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 IR3553 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 CBOOST

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 IR3553 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 CVCC

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 IR3553 and as close as possible to the VCC and

PGND (pin 4). Low inductance routing between the VCC

capacitor and the IR3553 pins is required to minimize the

ringing between the BOOST and SW pins.

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 IR3553. The mounting height of

these capacitors must be considered when selecting their

package sizes.

HIGH OUTPUT VOLTAGE DESIGN

CONSIDERATIONS

The IR3553 is capable of creating output voltages above

the 3.3V recommended maximum output voltage as there

are no restrictions inside the IR3553 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 IR3553 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.

LAYOUT EXAMPLE

Contact International Rectifier for a layout example

suitable for your specific application.

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