PM8908 datasheet(20/28 Pages) STMICROELECTRONICS

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Application information

PM8908

20/28

DocID027688 Rev 3

with:



RDROOP is the resistor between the COMP pin and the REF pin (see also Figure 9)



ILOAD is the output current



GM is the transconductance of the amplifier (1 mS)



ACS is the current sense gain (53 mV/A)

Figure 9. Typical application with droop configuration

6.3

Non-droop setting

The advantage of a non-droop configuration is that the load regulation is flat. It can be

implemented by connecting a resistor (RC) and a capacitor (CC) between the COMP pin and

the REF pin (see also Figure 1 on page 4).

6.4

Inductor design

The inductance value is defined by a compromise between the dynamic response time, the

efficiency, the cost, and the size. The inductor must be calculated to maintain the ripple

current (

I

L) between 20% and 30% of the maximum output current (typ.). The inductance

value can be calculated with the following relationship:

Equation 5

where fSW is the switching frequency, VIN is the input voltage, and VOUT is the output

voltage.

RPGOOD

PM8908

PGOOD

MODE

VOUT

COMP

REFIN

PGND

PHASE

BOOT

VIN

VCC

GND

VIN = 1 V to 3.5 V

VCC = 5 V

CBOOT

COUT

CVIN

CVCC

4, 5

1, 2, 3

11, 12, 13,

14, 15

RDROOP

REF

CREF

VOUT

OUT

–

I



------------------------------

OUT

--------------



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