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PDF PM8800 Data sheet ( Hoja de datos )
| Número de pieza | PM8800 | |
| Descripción | Integrated IEEE 802.3af compliant PoE-PD interface and PWM controller | |
| Fabricantes | STMicroelectronics | |
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PM8800
Integrated IEEE 802.3af compliant PoE-PD interface
and PWM controller with support of external source
Preliminary Data
Features
■ IEEE 802.3af compliant PD Interface
■ Works with power supplied from Ethernet LAN
cables or from local auxiliary sources
■ Integrated 100V, 0. 5Ω, 800mA Hot-Swap
MOSFET
■ Integrated signature resistor
■ Programmable in-rush current limit
■ Programmable classification current
■ Programmable DC current limit up to 800 mA
■ High voltage start-up bias regulator
■ Thermal Shutdown protection
■ Current mode pulse width modulator
■ Programmable Oscillator Frequency
■ Programmable Soft-start
■ Power Good Indication
■ 80% maximum duty cycle with internal slope
compensation
■ Supports both Isolated and Non-Isolated
Applications.
Applications
■ VoIP phones, WLAN access points
■ Security cameras
■ PoE Powered Device Appliances
■ High power (>12.95W) powered devices
Table 1. Device summary
Order codes
PM8800A
PM8800A
Max duty
80%
HTSSOP16
Description
The PM8800 integrates a standard Power over
Ethernet (PoE) interface and a current mode
PWM controller to simplify the design of the
power supply sections of all Powered Devices.
The PoE interface incorporates all the functions
required by the IEEE 802.3af including detection,
classification, under-voltage lockout (UVLO) and
in-rush current limitation.
PM8800 specifically targets PD with extended
power requirement with respect to the limit
imposed by the 802.3af standard, embedding a
hot-swap MOSFET capable of sustaining twice
the current of the 802.3af standard with a pro-
grammable DC current limit
The integrated switching regulator of the PM8800
has been designed to work with power either form
the Ethernet cable connection or from an external
power source such as AC adapter.
The DC/DC section of the PM8800 features a pro-
grammable oscillator frequency, soft-start, slope
compensation and embeds a voltage output error
amplifier allowing use in both isolated and non
isolated configuration.
Package
HTSSOP16
Packaging
Tube
Tape and reel
September 2007
Rev 1
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to
change without notice.
1/10
www.st.com
1
1 page  
PM8800
Pins description and connection diagrams
Table 1.
Pin n
6
7
8
9
10
11
12
13
14
15
16
Pin description (continued)
Name
Function
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 val-
ues. A resistance between this pin and VSS will set the level of inrush
current limit.
DCCL
DC Current Limit.
A resistor between DCCL and VSS will set the current limit for the inter-
face section of the PM8800. It can be set to exceed the IEEE802.3af
current limit . Leave the pin open for standard IEEE 802.3af applica-
tions
VSS
GND
System low potential input.
System return for the PWM converter.
It is the drain of the internal hot-swap power MOSFET.
GD
VCC
Output of the PWM controller. External power MOSFET gate driver out-
put
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
shutdown, reducing the controller power dissipation
nPGD
CS
PowerGood, active low
A high to low transition indicates that handshake with the PSE has
been successfully terminated and the SMPS portion of the PM8800 can
be activated
Current sense input.
Current sense input for current mode control and over-current protec-
tion. Current limiting is obtained with a dedicated current sense com-
parator. If the CS pin voltage exceeds 0.5V 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 Modula-
tor.COMP pull-up is provided by an internal 2.5kΩ resistor which may
be used to bias an opto-coupler transistor.
Feedback signal.
VFB Inverting input of the internal error amplifier. The non-inverting input is
internally connected to a 1.25V reference.
AGND
Analog PWM supply return.
GND for sensitive analog circuitry including the SMPS current limit cir-
cuitry. Must be connected to GND to improve noise immunity.
Exposed Pad.
EP Connect this to a board plane to improve heat dissipation; must be
electrically connected to VSS
5/10
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| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet PM8800.PDF ] | |
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