LP3925 Datasheet, PDF(24/51 Page) Texas Instruments – High Performance Power Management Unit for Handset Applications

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LP3925 Datasheet, PDF (24/51 Pages) Texas Instruments – High Performance Power Management Unit for Handset Applications

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EXTERNAL COMPONENT SELECTION

Default values for external components of LP3925 bucks are

input and output capacitances CIN = COUT = 4.7 ÂµF and in-

ductor L=1ÂµH whit the lowest possible DCR (less than 50

mâ¦). Below is the table with the selection of suitable inductors

for the application. With the carefull selection of the output

components the performance of the buck will not degrade in

stability, ripple, load regulation and transient aspects. The in-

ductor current (IL) and output voltage (VOUT) ripples are di-

rectly dependent on the external components. Current ripple

is mainly dependent on the inductance L

For example if use the combination L = 0.47 ÂµH (DCR = 50

mâ¦) and COUT = 30 ÂµF (ESR = 10 mâ¦), when VIN = 3V and

VOUT = 1.8V with load current of 600 mA, the theoretical peak

to peak current ripple should be:

while the RMS peak-to-peak voltage ripple should be in the

region of:

where fSW is the buckâs switching frequency and RPdson is the

drain to source resistance of the PMOS power switch. Voltage

ripple on the other hand has 2 main components.

One dependent on output capacitance:

The other is due to capacitor's ESR

The resulting RMS ripple is

DVS CONTROL

DVS allows a buck regulator to step between pre-pro-

grammed voltage values, using multifunctional pins as selec-

tors. DVS is supported for Buck1 and Buck2. They can have

up to 4 pre-programmed values, which are set in registers

BUCKn VOUTn.

Multifunctional pins can be set as single DVS selectors (1 se-

lecting signal) or dual DVS selectors (2 selecting signals).

DVS-controlling pins must be set as Buck1 DVS (code 0101)

or Buck2 DVS (code 0110) pins in their control registers

(named GPIOnn).

Any multifunctional pin can be used as a single DVS signal.

The signal selects between VOUT0 (input low) and VOUT1

(input high).

Dual DVS signals can only be predetermined pairs, the func-

tion description can be seen in the table below.

OSC_32KHZ

SIM_RST_IN

SIM_DATA

SIM_CLK

TCXO1_I

TCXO2_I

OE_N

SE0/VM

SPND

INP2

SINK2

Dual DVS Control Table for Bucks 1 and 2

RSENSE

SIM_CLK _IN

SIM_RST

SIM_IO

TCXO1_O

TCXO2_O

DATA/VP

RCV

INP1

SINK1

SINK3

BUCK1,2 VOUT

VOUT0

VOUT1

VOUT2

VOUT3

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