PM8800ATR STMicroelectronics, PM8800ATR Datasheet - Page 22

• Manufacturer Part Number: PM8800ATR
• Description: IC POE-PD PWM CTLR 16-HTSSOP
• Manufacturer: STMicroelectronics

Specifications of PM8800ATR

• Applications: Power Over Ethernet (PoE)
• Interface: IEEE 802.3af
• Voltage - Supply: 10 V
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Mounting Type: Surface Mount
• For Use With: 497-6366 - BOARD EVAL FOR PM8800A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6897-2; PM8800ATR

PD interface
5.7
22/35
Power good indication
The PM8800A embeds a power good circuit that is used to indicate that PWM input
capacitors are fully charged and that the switching regulator can start operation. The power
good circuit monitors the status of the internal hot-swap MOSFET and nPGD, an active low
signal is asserted when its V
good circuit includes hysteresis to allow the PM8800A to operate near the current limit point
without inadvertently disabling nPGD. The MOSFET voltage must increase to 3 V before
nPGD is disabled.
An internal comparator monitors the status of the nPGD pin and the PWM controller will be
running until the voltage at this pin goes above 2 V.
The power good indication is exposed at nPGD pin with a open drain, 45 Ω MOSFET so that
board designers can put a LED and a series current limiting resistor from the VCC pin to the
nPGD pin to indicate that the PD is powered from the PoE network.
Since the power good signal is internally used to activate the PWM controller, to avoid that
transients on the input voltage could produce intermittent operation of the PWM controller,
board designer can connect a capacitor C
mask the nPGD signal for a duration that can be estimate by the following equation:
where 30 µA is an internal current source that act as pull-up on the nPGD pin and I
current flowing through the external LED, if present.
∆t µs
(
)
=
----------------------------------------------------------
(
0.03mA
(
2V C
⋅
+
PGD
I
LED
(
nF
(
mA
)
)
)
DS
)
voltage falls below 1.5 V and V
PGD
between the nPGD pin and GND. This will
GS
rise above 2 V. The power
PM8800A
LED
is the