Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Comments on Rick Brooks' "simple" template for resistive discovery

Rick et alia:

Overall, the proposed signature template,  and the appended conditions,
looks straightforward and easy to work to. After a first look, I have just
these two comments:

a)	I believe that a pair of diodes drops - a maximum series voltage of
TBD Volts (probably 1.8V or 2.0V) should be allowed in series with R_sig.
This is a bit different from your Signature Resistance, Note 4.
b)	For PSE Discovery Specifications,  Note 5 (The PSE must be able to
sustain the condition of being driven by +/- 60 VDC continuously): I think
that this needs a maximum DC current specified, or the comment should be
added that the current in question may be theoretically unlimited.
Otherwise, it leaves some ambiguity as to how much protection is required
for reverse current into any PSE port.


[The following are included for reference from Rick Brook's "A 'simple'
template for resistive discovery" message. - PHS]

Signature Resistance -- Ohms

The maximum value of R_sig should not exceed 60 Kohm (value?) so as not to
intersect the minimum output impedance of a PSE
2) R_sig must be capable of handling 60 VDC continuously, or have a means of
disconnecting once DTE power is applied
3)Having different "flavors" of discovery, to indicate expected power
requirements can be accommodated by using different values of R_sig (this
has not been accepted yet as a goal for DTE Power)
4) R_sig should not be in series with any diodes, such as bridge rectifier
diodes (this should make detection simpler)


PSE Discovery Specifications:

1) PSE Discovery Output Impedance must be greater than 70 Kohm for any
frequency below 100 Hz, whether or not the PSE power is on, and whether or
not the discovery process is running
2) The PSE Discovery output capacitance must be less than 10 uF (value?)
3) The PSE discovery compliance voltage; must include at least one detection
with an open circuit voltage that is
above 20 volts. This will help to reject legacy devices with 24V power
4) The PSE discovery compliance voltage must not exceed 30 volts (value) at
any time, in order to avoid reaching the
power up range of the PD power supply
5) The PSE must be able to sustain the condition of being driven by +/- 60
VDC continuously
6) The PSE must never falsely detect another PSE (goal)

Peter Schwartz
Phone:	408.435.2460