PM8800 STMICROELECTRONICS | Alldatasheet

Document overview

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Technical content

Datasheet sections

  • 1 Typical application cir cuit and block diagram
  • 1.1 Application circuits
  • 2 Pins description and connection diagrams
  • 2.1 Pin descriptions
  • 3 Device description and operation
  • 4 Package mechanical data
  • 5 Revision history

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

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. HTSSOP16 Table 1. Device summary

1 Typical application circuit and block diagram

1.1 Application circuits

Figure 1. Simplified application schematic fo r powered device using PM8800 in isolated Figure 2. Simplified application schematic for Powered Device using PM8800 in non-isolated

2 Pins description and connection diagrams

Figure 3. Pins connection (top view)

2.1 Pin descriptions

Table 1. Pin description

1 RT/SYNC

Oscillator timing resistor pin and synchronization input. pulses from an external clock. System high potential input. it is the most positive input potential.

5 RCLASS

Classification resistor pin.

6 AUXI_IRL

In-rush current limit and auxiliary source enable pin.

7 DCCL

8 VSS System low potential input. 9G N D System return for the PWM converter. It is the drain of the internal hot-swap power MOSFET.

11 VCC

Output of the internal high voltage regulator.

14 COMP

be used to bias an opto-coupler transistor.

15 VFB

internally connected to a 1.25V reference.

16 AGND

cuitry. Must be connected to GND to improve noise immunity. Table 1. Pin description (continued)

3 Device description and operation

power with respect to the 12.95W allowed by standard PSE. detached when classification is over, in order to save power. mode (UVLO rising) or recognize disconnection (UVLO falling). Figure 4. State diagram of the PM800 interface depending on the input voltage PM8800 wait for the input voltage to overpass the UVLO voltage. on the proper programming resistor. 802.3af and can reach up to 800mA.

PM8800 Device description and operation PM8800 can work with power either from PoE networks or from auxiliary sources - like AC adapters -. Alternative sources are present in PoE appliances where devices can work also outside the context of the PoE networks or to ensure normal operation even if PoE becomes unavailable. PM8800 limits the number of external components to handle the coexistence of both PoE and auxiliary supplies. External sources can be connected so to exploit the in-rush current limitation provided by the MOSFET or enabling the PWM section, bypassing the interface section. A state-of-the-art current mode pulse with modulator is embedded in the PM8800 to support low side single ended isolated and non isolated topologies. A high gain bandwidth product error amplifier is embedded for non isolated configuration. The PWM switching frequency of PM8800 is programmable with an appropriate resistor and it is also capable of working with an external clock reference.

4 Package mechanical data

conditions are also marked on the inner box label. ECOPACK is an ST trademark. Figure 5. HTSSOP16 package mechanical data

5 Revision history

Table 2. Document revision history