IR3575 datasheet(17/23 Pages) IRF

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June 20, 2012 | FINAL DATASHEET | V1.1

IR3575

60A Exposed Top Integrated PowIRstage®

If any of the application condition, i.e. input voltage,

output voltage, switching frequency, VCC MOSFET driver

voltage or inductance, is different from those of Figure 8, a

set of normalized power loss curves should be used.

Obtain the normalizing factors from Figure 10 to Figure 14

for the new application conditions; multiply these factors

by the power loss obtained from Figure 8 for the required

load current.

As an example, the power loss calculation procedures

under different conditions, VIN=10V, VOUT=1V, ƒSW = 300kHz,

VCC=5V, L=210nH, VCC=5V, IOUT=40A, TAMBIENT = 25°C, no

heat sink, and no air flow, are as follows.

1) Determine the power loss at 40A under the default

test conditions of VIN=12V, VOUT=1.2V, ƒSW = 400kHz,

L=150nH, VCC=7V, TAMBIENT = 25°C, no heat sink, and no

air flow. It is 4.8W from Figure 8.

2) Determine the input voltage normalizing factor with

VIN=10V, which is 0.96 based on the dashed lines in

Figure 10.

3) Determine the output voltage normalizing factor with

VOUT=1V, which is 0.92 based on the dashed lines in

Figure 11.

4) Determine the switching frequency normalizing factor

with ƒSW = 300kHz, which is 0.98 based on the dashed

lines in Figure 12.

5) Determine the VCC MOSFET drive voltage normalizing

factor with VCC=5V, which is 1.16 based on the dashed

lines in Figure 13.

6) Determine the inductance normalizing factor with

L=210nH, which is 0.95 based on the dashed lines in

Figure 14.

7) Multiply the power loss under the default conditions

by the five normalizing factors to obtain the power

loss under the new conditions, which is 4.8W x 0.96 x

0.92 x 0.98 x 1.16 x 0.95 = 4.58W.

SAFE OPERATING AREA

Figure 9 shows the IR3575 safe operating area with the

case temperature controlled at or below 125°C. The test

conditions are VIN=12V, VOUT=1.2V, ƒSW=400kHz, L=150nH

(0.29mΩ), VCC=7V, TAMBIENT = 0°C to 90°C, no heat sink, and

Airflow = 0LFM / 100LFM / 200LFM / 400LFM.

If any of the application condition, i.e. input voltage,

output voltage, switching frequency, VCC MOSFET driver

voltage, or inductance is different from those of Figure 9, a

set of IR3575 case temperature adjustment curves should

be used. Obtain the temperature deltas from Figure 10 to

Figure 14 for the new application conditions; sum these

deltas and then subtract from the IR3575 case

temperature obtained from Figure 9 for the required load

current.

8) From Figure 9, determine the highest ambient

temperature at the required load current under the

default conditions, which is 77°C at 40A with 0LFM

airflow and the IR3575 case temperature of 125°C.

9) Determine the case temperature with VIN=10V, which

is -0.6° based on the dashed lines in Figure 10.

10) Determine the case temperature with VOUT=1V, which

is -1.2° based on the dashed lines in Figure 11.

11) Determine the case temperature with ƒSW = 300kHz,

which is -0.3° based on the dashed lines in Figure 12.

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

is +2.4° based on the dashed lines in Figure 13.

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

is -0.8° based on the dashed lines in Figure 14.

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

-0.6° -1.2° -0.3° +2.4° -0.8° = -0.5°. Deduct the delta

from the highest ambient temperature in step 8), 77°C

- (-0.5°C) = 77.5°C.

INDUCTOR CURRENT SENSING CAPACITOR CCS

AND RESISTOR RCS

If the IR3575 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.



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