PM8800ATR datasheet(7/35 Pages) STMICROELECTRONICS

7 / 35 page

PM8800A

Pins description and connection diagrams

7/35

7DCCL

DC current limit.

A resistor between DCCL and VSS will set the current limit for the interface

section of the PM8800A. It can be set to exceed the IEEE802.3af current limit.

Leave the pin open for standard IEEE 802.3af applications.

VSS

System low potential input.

9GND

System return for the PWM converter.

It is the drain of the internal hot-swap power MOSFET.

Output of the PWM controller. External power MOSFET gate driver output.

VCC

Output of the internal high voltage regulator.

When the auxiliary transformer winding (if used) raises the voltage on this pin

above the regulation set point, the internal regulator will be switched off, reducing

the controller power dissipation.

nPGD

Power good, active low signal.

A high to low transition indicates that the inrush current phase has been

completed, the internal hot swap MOSFET is fully closed and the SMPS portion of

the PM8800A is activated.

Current sense input.

Current sense input for current mode control and over-current protection. Current

limiting is obtained with a dedicated current sense comparator. If the CS pin

voltage exceeds 0.5 V the GD pin switches low for cycle-by-cycle current limiting.

Leading edge blanking is implemented to mask current spikes.

COMP

The output of the error amplifier and input of the Pulse Width Modulator.

COMP pull-up is provided by an internal 2.5 k

Ω resistor which may be used to

bias an opto-coupler transistor.

VFB

Feedback signal.

Inverting input of the internal error amplifier. The non-inverting input is internally

connected to a 1.25 V reference.

If not used must be grounded to AGND.

AGND

Analog PWM supply return.

GND for sensitive analog circuitry including the SMPS current limit circuitry. Must

be connected to GND to improve noise immunity.

Exposed pad.

Connect this to a board plane to improve heat dissipation; must be electrically

connected to VSS

Table 2.

Pin description (continued)

Pin#

Name

Function

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