AN4092 datasheet(11/38 Pages) STMICROELECTRONICS

11 / 38 page

AN4092

Power Management Controller (PMC)

Doc ID 023080 Rev 2

11/38

1.1.6

Inrush current

Since big capacitors need to be charged, a large current can be required when the power is

turned on, to be more precise when the 1.2V regulator is switched on.

A soft-start circuitry is included in the 1.2V regulator but the ramp is only limited to 60-80us

(PVT variation), being ineffective for limiting the inrush current.

As already pointed out in the Section 1.1.4, the resistor on the collector may or may not be

required depending on the allowable power dissipation of the ballast transistor. However the

resistor on the collector can be also very useful in limiting the current necessary to charge

the capacitors during power on.

Creg

10uF

Depending on the 5V regulator impedance,

the required capacitor can go up to 100uF

1.1Ohm

5.6Ohm

May or may not be required. It depends on

the allowable power dissipation of T1

0.18Ohm

0.2Ohm

0.22Ohm

+/-10% The required value can be obtained

by using more resistors in parallel

Table 1.

External network specification (continued)

External component

Min.

Typ.

Max.

Notes

Table 2.

Miscellaneous decoupling caps

Supply

Quantity

Value

Notes

VRC33

470nF - 2uF

Low ESR (<50mOhm)

VSTBY

10nF

To be grounded if the Stand-by feature is

not used.

VDDPLL

100nF

10nF

VDDEHx

100nF

Two pairs each side

1nF

VDDA

10uF

To be connected between VDDA and

VSSA

VRH

10nF

VRL

VSSA

REFBYPC

100nF

REFBYPC is not a supply. The external

bypass capacitor must be placed between

REFBYPC pin and GND.

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