LM5071MT-50 NSC [National Semiconductor], LM5071MT-50 Datasheet - Page 14

• Manufacturer Part Number: LM5071MT-50
• Description: Power Over Ethernet PD Controller with Auxiliary Power Power Over Ethernet PD Controller with Auxiliary Power
• Manufacturer: NSC [National Semiconductor]

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Gate Driver and Maximum Duty
Cycle Limit
plished with an internal toggle flip-flop which ensures an
accurate duty cycle limit. The internal oscillator frequency of
the LM5071-50 is therefore twice the operating frequency of
the PWM controller (OUT pin).
The 80% maximum duty cycle limit of the LM5071-80 is
determined by the internal oscillator and varies more than
the 50% limit of the LM5071-50. For the LM5071-80, the
internal oscillator frequency and the operational frequency of
the PWM controller are equal.
Thermal Protection
Internal thermal shutdown circuitry is provided to protect the
integrated circuit in the event the maximum junction tem-
(Continued)
14
perature is exceeded. This feature prevents catastrophic
failures from accidental device overheating. When activated,
typically at 165 degrees Celsius, the controller is forced into
a low power standby state, disabling the output driver, bias
regulator, main interface pass MOSFET, and classification
regulator if enabled. After the temperature is reduced (typical
hysteresis = 25˚C ) the V
softstart sequence initiated.
Thermal shutdown is not enabled during auxiliary power
operation as the power MOSFET is not running any current
and should not experience an over-temperature condition. If
the drain of the MOSFET exceeds 2.5V with respect to VEE
(internal Power Good de-assertion), PoE UVLO becomes
de-asserted (insertion of PoE or other 48V supply), or the
auxiliary power is removed, thermal limit will be re-enabled
immediately.
CC
regulator will be enabled and a