(

)

(

)

RIPPLE1

OC

OUT1

I

2.5 A

V

I

1.2

DCR

1.2

10 A

1.2

3.15 m

1.2

51.05 mV

2

2

é

ù

é

ù

æ

ö

æ

ö

=

+

´

´

´

=

+

´

´

W ´

=

ê

ú

ê

ú

ç

÷

ç

÷

è

ø

è

ø

ë

û

ë

û

(

)

(

)

(

)

(

)

OC

CS max

OS min

ILIM

ILIM(min)

V

V

A

V

51.05 mV

16

3 mV

V

R

86.29 k

86.6 k

I

9.5 A

´

-

´

- -

=

=

=

W »

W

m

FB

OUT1

FB

V

R10

0.600 V

20.0 k

R14

20 k

V

V

1.2 V

0.600 V

´

´

W

=

=

=

W

-

-

(

)

G1

BOOST

BOOT ripple

Q

7 nC

C

70 nF

100 nF

V

100 mV

=

=

=

»

9

9

RT

SW

20

20

R

40 k

40.2k

f

500 kHz

=

=

=

W »

W

TPS40322

SLUSAF8

– JUNE 2011

www.ti.com

(23)

(24)

Feedback Divider (R10, R14)

The TPS40322 controller uses a full operational amplifier with an internally fixed 0.600-V reference. Tha value for

R10 is selected between 10-k

Ωand 50-kΩ for a balance of feedback current and noise immunity. With the R10

resistor set to 20-k

Ω, the output voltage is programmed with a resistor divider given by Equation 25.

(25)

Compensation: (R11, R12, C17, C19, C21)

Using the TPS40k Loop Stability Tool for an 85-kHz bandwidth and 50

° of phase margin with an R10 value of

20.0 k

Ω, and measuring the theoretical results in the laboratory and modifying accordingly for system

optimization yields the following values.

•

C21 = 10 pF

•

C17 = 220 pF

•

C19 = 470 pF

•

R12 = 4.42 k

Ω

•

R11 = 82.5 k

Ω

Boot-Strap Capacitor (C7)

To ensure proper charging of the high-side FET gate, limit the ripple voltage on the boost capacitor to

< 100 mV.

(26)

General Device Components

Synchronization (SYNC Pin)

The SYNC pin can be left open for independent dual outputs.

RT Resistor (R6)

calculated using Equation 27.

(27)

Differential Amplifier Out (DIFFO Pin)

In dual output configuration the DIFFO pin is not used and must remain open (unconnected).

EN/SS Timing Capacitors (C8)

The soft-start capacitor provides smooth ramp of the error amplifier reference voltage for controlled start-up. The

soft-start capacitor is selected using Equation 28.

24

Copyright

© 2011, Texas Instruments Incorporated