PM8805 datasheet(24/45 Pages) STMICROELECTRONICS

24 / 45 page

PM8805 overview

PM8805

24/45

DS12813 Rev 1

4.7

Hot swap, CTRL and PGD pins

Above UVLO threshold, when the internal charge pump is turned on, an internal current

source is used to charge the output capacitor (e.g. the input capacitor of the DC/DC

converter) in order to control the inrush current.

The internal current source is only active during the charge phase of the output capacitance,

with a 25 mA typ. current when (VOB-VOUT) = 55 V or more, which linearly increases up to

140 mA when the voltage across the hot swap MOSFET falls below 7 V.

Note that the internal current source is not capable of sustaining any extra load applied on

VOUT (such as a PWM controller quiescent current), since its only purpose is the charge of

Cout. The load can be applied only after the complete charge of the output capacitor (i.e.

when PGD signal is asserted).

It is recommended to limit the maximum quiescent current used as a load on VOUT before

PGD assertion to 10 mA (Iload_inrush). The more current used to bias output loads, the

slower the inrush phase is.

A simplified formula for the current is:

Equation 1

A simplified formula for the average current is:

Table 9. PD main parameters table

type

Class

CLS1

sign.

CLS2

sign.

(W)

Vin min.

(V)

Vin max.

(V)

Iin max.

(mA)

Ppeak

( W )

for 50ms

13.0

37.0

350

14.4

3.84

42.1

5.00

6.49

40.8

160

8.36

13.0

37.0

350

14.4

25.5

42.5

600

28.05

3.84

42.1

5.00

6.49

40.8

160

8.36

13.0

37.0

350

14.4

25.5

42.5

600

28.05

40.0

44.3

900

51.0

42.5

1200

53.55

62.0

42.9

1440

65.10

71.3

41.2

1730

74.86

I = (25mA-Iload_inrush) + 2.4[mA/V] * [55 - (VOB - VOUT)]

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