hv110 Supertex, Inc., hv110 Datasheet - Page 7

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

pass element, and initiate an auto-restart sequence,
with a 9 second interval as shown in Figure 6. In the
event the over-current is cleared before the over-
current timer has expired, then the over-current timer
will be reset and the device will start to function
normally.
DC Disconnect
HV110 includes an under-current detection circuit to
disconnect the PD when the current falls below the
under-current threshold level. HV110 will turn the
internal FET OFF if the load current falls below a
threshold level of 10mA (nominal) for a period
determined by the under-current timer (Signature
drop-out time, t
applications, this acts as an additional protection to
help overcome rapid reinsertion of a legacy or a non-
compliant device.
HV110 provides most of the safety and timing
requirements of a PSE in PoE applications hence
can be considered as a secondary/redundant stage
to comply with the IEEE 802.3af standards for the
Powered Device. One motivation for this is that the
PSE is an unknown quantity and may not be fully
IEEE802.3af compliant in all cases. HV110 will
ensure that valuable PD devices are not damaged
and that they fulfill the IEEE802.3af compliance.
Turning on to a large C
The PSE is required to limit the start up currents for
C
standard. For higher value of C
the current. Figure 8 shows that the HV110 limiting
port
less than 180µF only, as per the IEEE802.3af
Figure 6. Auto-restart into a shorted output
UC
350ms nominal). In Class 0
port
port
, the PD has to limit
7
current into 300µF as required by the IEEE802.3af
specification.
To allow charging of extremely large capacitors, the
HV110 includes a feature that will disable the turn on
timers, PWRGD and Timeout. This feature is based
on the turn on voltage slew rate (Vslew). If Vslew is
kept below 4.25V/ms then the timers are disabled
and limiting will occur indefinitely until C
charged. This will also, however, disable PWRGD
that is enabled by the same timer. In most cases the
capacitor used in PD application is well below 180uF
so this feature is not of much significance in a PD
application.
Figure 7. Undercurrent shutdown when current falls
Figure 7. HV110 turning on to a 300uF Cport, still maintaining
still maintaining the maximum input current of 400mA
Figure 8. HV110 turning on into a 300uF Cport,
the maximum input current of 400mA, does not need any
(without any additional components required)
from 12mA to 9mA
additional current limiting elements in the PD
I
DRAIN
PWRGD
nput Voltage
Current
Input Current
DRAIN
HV110
A061104
port
is