SLVSF02D March 2019 – May 2020 TPS23881
COMMAND = 50h with 1 Data Byte, Read/Write
|LEGEND: R/W = Read/Write; R = Read only; -n = value after reset|
|7 - 4||MACn||R/W||0||Manual Auto Class Measurement bits
1 = Manual Auto Class Measurement enabled
0 = Manual Auto Class measurement complete
The auto class measurement will begin within 10ms of this bit being set.
This bit will be cleared by the internal firmware within 1ms of the updated Autoclass measurement result(s) in 0x51-54h.
|3 -0||AACn||R/W||0||Auto Class Auto Adjustment Enable bits
1 = Autoclass auto adjust is enabled and the corresponding PCUT settings will be automatically adjusted based on the measured autoclass power
0 = Autoclass auto adjust is disabled and it is up to the user to adjust the value of PCUT as desired.
Any MACn bits set prior to turn on will be ignored and cleared during turn on.
Auto Class Pcut Adjustments:
If the ACx bit(s) are set in register 0x50h, the TPS23881 will automatically adjust its PCUT value based on the auto class power measurement (PAC in registers 0x51-54) and Any Automatic Auto Class facilitated (AACn = 1) PCut adjustments will be made within 5 ms of the end of the auto class measurement period.
If the AACn bits are not set, the table and equations below should be used to make any PCUT adjustments based on the auto class power measurement (PAC).
|Auto Class Measured Power (PAC)||PAC_MARGIN|
|PAC < 18.5 W||0.5 W|
|19 W < PAC < 25.5 W||1 W|
|26 W < PAC < 36.5 W||2 W|
|36.5 W < PAC < 45W||3 W|
|45 W < PAC < 51.5 W||4 W|
|51.5 W < PAC < 58 W||5 W|
|58 W < PAC < 63W||6 W|
|63 W < PAC < 68 W||7W|
|68 W < PAC < 73 W||8W|
|PAC > 73 W||9W|
For a PSE supporting Auto Class, the PAC_MARGIN is an IEEE required surplus of power over the measured power during auto class that allows for component degradation over time.
For 2-Pair or Dual Signature 4-Pair PDs, only the 2P-PCut values will be updated based on each pair sets measured PAC according to the equation below.
2P-PCut = PAC + PAC_MARGIN
For Single signature 4-Pair PDs, the sum of the autoclass power measurements on each pair set will be used to determine the 4P-PCut setting according to the equation below:
4P-PCut = PAC_ALTA + PAC_ALTB + PAC_MARGIN
For Single signature 4-Pair PDs, the auto class measurements will have no impact on the 2P-PCut settings. These values will remain unchanged from the 2P-Pcut settings prior to the start of the auto class measurement.
For 4-pair wired ports with single signature connected devices:
if only one AACn bit is set and an autoclass power measurement is completed (manual or during turn on), the 4-PCut value will still be updated based on the power measurement
If only one MACn bit is set, no autoclass measurement will be completed.
If the result of PAC + PAC_MARGIN is above a Channel’s assigned classification range, no changes will be made to the either the 2P or 4P Pcut settings.