lm5072mhx-80 National Semiconductor Corporation, lm5072mhx-80 Datasheet - Page 10

• Manufacturer Part Number: lm5072mhx-80
• Description: Integrated 100v Power Over Ethernet Pd Interface And Pwm Controller With Aux Support
• Manufacturer: National Semiconductor Corporation

www.national.com
Description of Operation and
Applications Information
The LM5072 integrates a fully IEEE 802.3af compliant PD in-
terface and PWM controller in a single integrated circuit,
providing a complete and low cost power solution for devices
that connect to PoE systems. The implementation requires a
minimal number of external components.
The LM5072’s Hot Swap PD interface provides four major
advantages:
1.
2.
3.
An input voltage rating up to 100V that allows greater
flexibility when selecting a transient surge suppressor to
protect the PD from voltage transients encountered in
PoE applications.
The integration of the PD signature resistor and other
functions including programmable inrush current limit,
input voltage under-voltage lock-out (UVLO), PD
classification, and thermal shutdown simplifies PD
implementation.
The PD interface and PWM controller accept power from
auxiliary sources including AC adapters and solar cells
in various configurations and over a wide range of input
voltages. Auxiliary power input can be programmed to be
dominant over PoE power.
FIGURE 2. PWM Controller Block Diagram
10
4.
The LM5072 includes an easy to use PWM controller based
on the peak current mode control technique. Current mode
control provides inherent advantages such as line voltage
feed-forward, cycle-by-cycle current limit, and simplified
closed-loop compensation. The controller’s PWM gate driver
is capable of sourcing and sinking peak currents of 800 mA
to directly drive the power MOSFET switch of the DC-DC
converter. The PWM controller also contains a high gain, high
bandwidth error amplifier, a high voltage startup bias regula-
tor, a programmable oscillator for a switching frequency be-
tween 50 kHz to 500 kHz, a bias supply (V
lock-out circuit, and a programmable soft-start circuit. These
features greatly simplify the design and implementation of
single ended topologies like the flyback, forward and buck.
The LM5072 is available in two versions, the LM5072-50 and
LM5072-80. As indicated in the suffix of the part number, the
maximum duty cycle of each device is limited to 50% and
80%, respectively. Internal PWM controller slope compensa-
tion is provided in the LM5072-80 version.
DC current limit is programmable and adjustable to
support PoE applications requiring input currents up to
700 mA.
CC
20184616
) under-voltage