IR3551MTRPBF International Rectifier, IR3551MTRPBF Datasheet - Page 16

• Manufacturer Part Number: IR3551MTRPBF
• Description: The IR3551 integrated PowIRstage is a synchronous buck gate driver IC with co-packed control and synchronous MOSFETs and Schottky diode.
• Manufacturer: International Rectifier

Specifications of IR3551MTRPBF

• Package: PQFN / 5 x 6
• Iout (a): 50
• Switch Freq (khz): up to 1.0MHz
• Input Range (v): 4.5 - 15
• Output Range (v): 0.25 - (VCC -2.5)

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, V
VCC=5V, L=210nH, VCC=5V, I
heat sink, and no air flow, are as follows.
1) Determine the power loss at 35A under the default
2) Determine the input voltage normalizing factor with
3) Determine the output voltage normalizing factor with
4) Determine the switching frequency normalizing factor
5) Determine the VCC MOSFET drive voltage normalizing
6) Determine the inductance normalizing factor with
7) Multiply the power loss under the default conditions
SAFE OPERATING AREA
Figure 9 shows the IR3551 safe operating area with the
case temperature controlled at or below 125°C. The test
conditions are V
(0.29mΩ), VCC=7V, T
Airflow = 0LFM / 100LFM / 200LFM / 400LFM.
test conditions of V
L=150nH, VCC=7V, T
air flow. It is 4.5W from Figure 8.
V
Figure 10.
V
Figure 11.
with ƒ
lines in Figure 12.
factor with VCC=5V, which is 1.18 based on the dashed
lines in Figure 13.
L=210nH, which is 0.94 based on the dashed lines in
Figure 14.
by the five normalizing factors to obtain the power
loss under the new conditions, which is 4.5W x 0.96 x
0.92 x 0.99 x 1.18 x 0.94 = 4.4W.
IN
OUT
=10V, which is 0.96 based on the dashed lines in
=1V, which is 0.92 based on the dashed lines in
SW
16
= 300kHz, which is 0.99 based on the dashed
IN
=12V, V
March 12, 2012 | FINAL DATASHEET
AMBIENT
AMBIENT
IN
=12V, V
OUT
= 0°C to 90°C, no heat sink, and
IN
=1.2V, ƒ
OUT
=10V, V
= 25°C, no heat sink, and no
=35A, T
OUT
=1.2V, ƒ
OUT
SW
=400kHz, L=150nH
=1V, ƒ
AMBIENT
SW
SW
= 25°C, no
= 400kHz,
= 300kHz,
50A 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 9, a
set of IR3551 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 IR3551 case
temperature obtained from Figure 9 for the required load
current.
8) From Figure 9, determine the highest ambient
9) Determine the case temperature with V
10) Determine the case temperature with V
11) Determine the case temperature with ƒ
12) Determine the case temperature with VCC = 5V, which
13) Determine the case temperature with L=210nH, which
14) Sum the case temperature adjustment from 9) to 13),
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
with the inductor are chosen to match the time constant of
the inductor, and therefore the voltage across the
capacitor C
Measure the inductance L and the inductor DC resistance
R
L
. Pre-select the capacitor C
temperature at the required load current under the
default conditions, which is 72°C at 35A with 0LFM
airflow and the IR3551 case temperature of 125°C.
is -0.9° based on the dashed lines in Figure 10.
is -1.8° based on the dashed lines in Figure 11.
which is -0.2° based on the dashed lines in Figure 12.
is +4.0° based on the dashed lines in Figure 13.
is -1.4° based on the dashed lines in Figure 14.
-0.9° -1.8° -02° +4.0° -1.4° = -0.3°. Deduct the delta
from the highest ambient temperature in step 8), 72°C
- (-0.3°C) = 72.3°C.
CS
represents the inductor current.
CS
R
CS

CS
CS
L
C
and calculate R
and capacitor C
CS
R
L
IR3551
OUT
IN
SW
CS
=10V, which
CS
=1V, which
as follows.
= 300kHz,
in parallel
CS