lm5070sd-50 National Semiconductor Corporation, lm5070sd-50 Datasheet - Page 10

• Manufacturer Part Number: lm5070sd-50
• Description: Integrated Power Over Ethernet Pd Interface And Pwm Controller
• Manufacturer: National Semiconductor Corporation

www.national.com
Block Diagrams
Detailed Operating Description
The LM5070 power interface port and pulse width modula-
tion (PWM) controller provides a complete integrated solu-
tion for Powered Devices (PD) that connect into Power over
Ethernet (PoE) systems. Major features of the PD interface
portion of the IC include detection, classification, program-
mable inrush current limit, thermal limit, programmable und-
ervoltage lockout, and current limit monitoring. The device
also includes a high-voltage start-up bias regulator that op-
erates over a wide input range up to 75V. The switch mode
power supply (SMPS) control portion of the IC includes
power good sensing, V
cycle-by-cycle current limit, error amplifier, slope compensa-
tion, softstart, and oscillator sync capability. This high speed
BiCMOS IC has total propagation delays less than 100ns
and a 1MHz capable oscillator programmed by a single
external resistor. The LM5070 PWM controller provides
CC
regulator under-voltage lockout,
(Continued)
FIGURE 3. PWM Controller Block Diagram
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current-mode control for dc-dc converter topologies requiring
a single drive output, such as Flyback and Forward topolo-
gies. The LM5070 PWM enables all of the advantages of
current-mode control including line feed-forward, cycle-by-
cycle current limit and simplified loop compensation. The
oscillator ramp is internally buffered and added to the PWM
comparator input ramp to provide slope compensation nec-
essary for current mode control at duty cycles greater than
50% (-80 suffix only).
Modes of Operation
The LM5070 PD interface is designed to provide a fully
compliant IEEE 802.3af system. As such, the modes of
operation take into account the barrel rectifiers often utilized
to correctly polarize the dc input from the Ethernet cable.
Table 1 shows the LM5070 operating modes and associated
input voltage range.
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