製品概要
概要
This reference design represents a 3.3 V, 20 A converter solution ideal for various applications including wireless access points, supplied with a PoE-PD interface and a DC-DC active clamp forward converter.
The PoE-PD interface is based on the PM8805 system in package device with two active bridges and an IEEE 802.3bt compliant Powered Device (PD) interface. It can be used in all medium-to-high power 2P and 4P high efficiency PoE and PoE+ applications.
The DC-DC active clamp forward converter is designed around the PM8804 PWM controller, which is an integrated solution for smart and efficient 48 V converters, featuring a programmable oscillator for the switching frequency, adjustable slope compensation, dual complementary low-side drivers with programmable dead time, programmable soft start, soft turn off and a programmable current sense blanking time.
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特徴
- Features of the PM8805 PoE-PD interface:
- System in package integrating a double active bridge, a hot-swap MOSFET and a PoE-PD
- Supports legacy high power, 4-pair applications
- 100 V N-ch MOSFETs with 0.2 Ω total path resistance for each active bridge
- Identifies which kind of PSE (standard or legacy) it is connected to and provides successful IEEE 802.3af/at/bt classification indication as a combination of the T0, T1 and T2 signals (open drain)
- Smart operation mode selection through the STBY, FAUX and RAUX control signals
- QFN 56 8x8mm package with 43 pins and 6 exposed pads
- Features of the PM8804 PWM controller:
- PWM peak current mode controller
- Input operating voltage up to 75 V
- Internal high voltage start up regulator with 20 mA capability
- Programmable fixed frequency up to 1 Mhz
- Soft startup with settable time
- Soft turn off (optionally disabled)
- Dual 1 APK, low side complementary gate drivers
- GATE2 can be turned off for reduced consumption
- 80% maximum duty cycle with internal slope compensation
- QFN 16 3x3mm package with exposed pad
- Features of the PM8805 PoE-PD interface:
