hv110 Supertex, Inc., hv110 Datasheet - Page 9

• Manufacturer Part Number: hv110
• Description: Power-over-ethernet Interface Pd Controller Meets Ieee802.3af Tm Standard
• Manufacturer: Supertex, Inc.

Alternate Method for Powering HV110
The 12V zener diode connected to the V
HV110 (shown in Figure 1) is required to block the
IC in the Discovery process, so that the quiescent
current of the IC does not interfere with the signature
resistance detect.
12V drop across it causing the HV110 to see only
36V.
unusable. By using a PNP transistor, along with a
low power zener and resistor instead, the built-in
undervoltage thresholds can be utilized.
This makes the internal UV thresholds
However, this zener causes a
Figure 10. Powering HV110 using a PNP transistor instead of a zener
PP
pin of the
9
Figure 10 shows the modified circuit.
Discovery stage, the input voltage is less than 10V.
This causes the zener to be reverse biased and
hence there is no base current to the PNP transistor.
Once the input voltage increases beyond 12V, the
zener starts conducting, which provides a base
current path for the PNP transistor. The transistor
goes into the saturation region, essentially pulling
V
PP
to the rail.
HV110
A061104
In the