hv110 Supertex, Inc., hv110 Datasheet - Page 8

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

Application Circuits
Classification Option
Figure 9 above shows the schematic for a typical
classification scheme used with HV110. The PSE
identifies the Class of the PD, by measuring the
current flowing into R
Period.
The reference voltage at the base of the bipolar
transistor (the zener and resistor) should be chosen
to draw much less than 1mA so it does not interfere
with Classification levels. The zener temperature
coefficient is negative (if chosen below 4V) and the
V
first order temperature compensated reference
across R
the classification current.
Choose R
the PD load, using the formula:
where V
is the voltage across the b-e junction of the bipolar
transistor, I
corresponding to the power rating of the PD as
shown in Table 2 and I
HV110 (1mA). (* Signature resistance)
be
temperature coefficient is negative providing a
R
class
z
class
is the voltage rating of the Zener diode, V
= (V
class
class
. The (V
corresponding to the current level of
z
is the classification Signature current
-V
be
) / (I
z
-V
be
class
class
)/R
Q
- I
class
Quiescent current of the
during the Classification
Q
-17.5V / 25k*)
allows programming of
Figure 9. Classification Circuit with HV110
be
8
The above factors take into account the quiescent
chip current above the 12V zener voltage as well as
the Signature resistors in the mid-range of the
Classification probe voltage range. As the current
ranges are wide, it is possible to ensure that the
Classification current is within the ranges of the
Table 2 on Page 4 under all conditions.
however recommended that a voltage reference be
used instead of a zener diode as the voltage
reference will maintain the voltage across it over a
wide current range.
The diode from base to PWRGD turns off
classification as soon as PWRGD is pulled low to
save power. The zener in series with the HV110 will
keep the Classification components from drawing
current until after Discovery.
diode in series with the base of the bipolar transistor
can block the maximum expected differential
network voltage.
Table 3. R
Class
0
1
2
3
class
for different classes of PD
95.3 Ω
63.4 Ω
191 Ω
Open
R
class
Make sure that the
HV110
A061104
It is