OUT1

OUT1

IN1(min)

RIPPLE(cap)

IN(min)

SW

I

V

10 A

1.2 V

C

15 F

V

V

f

200 mV

8 V

500 kHz

´

´

=

=

=

m

´

´

´

´

(

)

RIPPLE(esr )

MAX

1

OUT1

RIPPLE1

2

V

50 mV

ESR

4.44 m

11.25 A

I

I

=

=

=

W

+

´

(

)

(

)

OUT1

RMS cin1

I

I

D

1

D

10 A

0.15

(1

0.15)

3.57 A

=

´

´

-

=

´

´

-

=

OUT1

IN(min)

V

D

V

=

m

=

=

=

W

´

m

´

W

DCR

L1

0.88 H

R13

2.8 k

C

V

0.1 F

3.15 m

(

)

(

)

(

)

´

=

-

CS max

DCR

CS max

R13

V

R15

V

V

(

)

(

)

(

)

=

´

´

´

DCR

L peak

V

DCR

1.2

I

1.3

TPS40322

www.ti.com

SLUSAF8

– JUNE 2011

A 744314110 from Wurth-Midcom with 1.1-

µH zero current inductance is selected. Inductance for this part is

0.88-

µH at 10 A bias. This 15-A, 3.15 mΩ inductor exceeds the minimum inductor ratings in a 7 mm x 7 mm

package.

Input Capacitor Selection (C3 through C6)

The input voltage ripple is divided between the capacitance and ESR of the input capacitor. For this design

using Equation 16.

(16)

(17)

The RMS current in the input capacitors is estimated using Equation 18.

(18)

(19)

To achieve these goals, two 0805, 10-

µF capacitors, one 0605, 1.0-µF capacitor and one 0402, 0.1-µF X5R

ceramic capacitor are combined at the input.

MOSFET Selection (Q1)

Texas Instruments CSD86330, 20-A power block device was chosen. This device incorporates the high-side and

8.8 m

used on the HDRV pin on each device for added noise immunity.

ILIM Resistor (R2)

The output current is sensed across the DCR of the L1 output inductor. An RC combination having a time

constant equal to that of the L1 inductance and the DCR is used to extract the current information as a voltage. A

standard capacitor value of 0.1-

µF is used. The resistor, R13, can be calculated using Equation 20.

(20)

A standard 3.09-k

Ω resistor was selected.

variation in the DCR value, then a resistor is added to divide the voltage down to 60 mV. The divider resistor,

R15, is calculated by Equation 21.

where

(22)

(22)

The TPS40322 uses the negative drop across the low-side FET at the end of the

“OFF” time to measure the

for self-heating of the MOSFET, the voltage drop across the low-side FET at current limit is given by

Equation 23.

Copyright

© 2011, Texas Instruments Incorporated

23