PM8800ATR datasheet(6/35 Pages) STMICROELECTRONICS

6 / 35 page

Pins description and connection diagrams

PM8800A

6/35

Pins description and connection diagrams

Figure 5.

Pins connection (top view)

2.1

Pin descriptions

VIN

RCLASS

HTSSOP-16

AGND

VFB

COMP

nPGD

VCC

GND

AUXII

DCCL

AUXI_IRL

VSS

Table 2.

Pin description

Pin#

Name

Function

1RT

Oscillator timing resistor pin and synchronization input.

An external resistor connected from RT to AGND sets the oscillator frequency.

This pin will also accept narrow ac-coupled synchronization pulses from an

external clock.

2SS

Soft-start input.

An external capacitor connected from SS and AGND and an internal

µA current source set the soft-start ramp rate. this pin is also used to set the

hiccup timer in case of overcurrent conditions. See Section 6 for detail.

3AUXII

Auxiliary source enable pin.

Use this pin to power up the DC/DC section only from the external source. The

auxiliary source can prevail over the PoE source depending on the value of the

resistor between this pin and the external source. See Section 7 for detail.

4VIN

System high potential input.

The diode “OR” of PoE line and auxiliary sources connected to the PD, it is the

most positive input potential.

RCLASS

Classification resistor pin.

Connect a classification programming resistor between this pin and VSS.

AUXI_IRL

In-rush current limit and auxiliary source enable pin.

Pulling up this pin to the auxiliary source will change the internal UVLO settings

and allow PD to be powered with voltage lower than nominal PoE voltages. In this

condition inrush current limit is set to default values. See Section 7 for details.

A resistance between this pin and VSS will set the level of inrush current limit.

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