§

·

u ¨

¸

¨

¸

©

¹

2

2

RIPPLE

RMSCIN

OUT

I

I

D

I

12

u

u

u

OUT

PPIN

OUT

CIN

IN

S

I

D

V

I

ESR

C

F

33

LM10504

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SNVS739F – DECEMBER 2011 – REVISED OCTOBER 2016

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Copyright © 2011–2016, Texas Instruments Incorporated

A simplified worst-case assumption is that all of the PFET current is supplied by the input capacitor. This results

in conservative estimates of input ripple voltage and capacitor RMS current.

Input ripple voltage is estimated with Equation 9.

where

•

VPPIN is the estimated peak-to-peak input ripple voltage

•

IOUT is the output current

•

CIN is the input capacitor value

•

ESRCIN is the input capacitor ESR

(9)

This capacitor is exposed to significant RMS current, so it is important to select a capacitor with an adequate

RMS current rating. Capacitor RMS current estimated with Equation 10.

where

•

IRMSCIN is the estimated input capacitor RMS current

(10)

8.2.2.2 Recommendations For Unused Functions and Pins

If any function is not used in the end application, see Table 8 for tying off the associated pins on the circuit

boards must be used.

Table 8. Unused Pin Recommendations

FUNCTION

PIN

IF UNUSED

BUCK1

VIN_B1

Connect to GND

SW_B1

Floating

FB_B1

Connect to GND

BUCK2

VIN_B2

Connect to GND

SW_B2

Floating

FB_B2

Connect to GND

BUCK3

VIN_B3

Connect to VIN

SW_B3

Floating

FB_B3

Connect to VIN

SPI

SPI_CS

Connect to VIN_IO

SPI_DI

Connect to GND

SPI_DO

Connect to GND

SPI_CK

Connect to GND

Vselect_B2

Connect to GND or leave open

Vselect_B3

Connect to VIN or leave open

DevSLP

Connect to GND or leave open

RESET

Connect to VIN_IO

COMPARATOR

VCOMP

Connect to VIN

Interrupt

Leave open