JAJSUD6 データシート

JAJSUD6 April 2024 TPS23881B

PRODUCTION DATA

8.1.5 Power Allocation and Power Demotion

The Power Allocation settings in register 0x29 sets the maximum power level a port powers on. Settings for each Class level from 2-pair 4 W (Class 1) up to 4-pair 90 W (Class 8) have been provided to maximize system design flexibility.

Note:

The Power Allocation settings in register 0x29 do not set the power limit for a given port. The port and channel power limiting is configured with the 2P (registers 0x1E- x 21) and 4P (0x2A - x2B) policing registers.

During a turn-on attempt, if a PD presents a classification level greater than the power allocation setting for a port, the TPS23881B limits the number of classification fingers presented to the PD prior to turn on based on the power allocation settings in register 0x29, known as Power Demotion. Power Demotion is the number of fingers presented to the PD that sets the maximum level of power the PD is allowed to draw before the PSE is allowed to disable it.

Note:

The IEEE 802.3 standard requires PDs that are power demoted by a PSE to limit their total power draw below the Type/class level set by the number of fingers presented by the PSE during mutual identification.

Power Demotion on a port is limited to the Type boundaries as the only means of communication from the PSE to the PD is the number of classification fingers prior to turn on.

1 finger = 15.4 W, 3 fingers = 30 W, 4 fingers = 60 W, and 5 fingers = 90W

Table 8-2 Single Signature PD Power Demotion Table

Power Allocation Register 0x29	Assigned Class Value (based on the PD connected at the port)
Power Allocation Register 0x29	Class 3 PD	Class 4 PD	Class 5 PD	Class 6 PD	Class 7 PD	Class 8 PD
4-Pair 15W	Class 3	Class 3	Class 3	Class 3	Class 3	Class 3
4-Pair 30W	Class 3	Class 4	Class 4	Class 4	Class 4	Class 4
4-Pair 45W	Class 3	Class 4	Class 5	Class 4	Class 4	Class 4
4-Pair 60W	Class 3	Class 4	Class 5	Class 6	Class 6	Class 6
4-Pair 75W	Class 3	Class 4	Class 5	Class 6	Class 7	Class 6
4-Pair 90W	Class 3	Class 4	Class 5	Class 6	Class 7	Class 8

Table 8-3 Dual Signature PD Power Demotion Table

Power Allocation Register 0x29	Assigned Class Value (based on the PD connected at the port)
Power Allocation Register 0x29	Class 3D PD		Class 4D PD		Class 5D PD
	Odd Channel (Primary)	Even Channel (Secondary)	Odd Channel (Primary)	Even Channel (Secondary)	Odd Channel (Primary)	Even Channel (Secondary)
4-Pair 15W	Class 3	Insufficient Power	Class 3	Insufficient Power	Class 3	Insufficient Power
4-Pair 30W	Class 3	Class 3	Class 4	Insufficient Power	Class 4	Insufficient Power
4-Pair 45W	Class 3	Class 3	Class 4	Class 3	Class 4⁽¹⁾	Class 3⁽¹⁾
4-Pair 60W	Class 3	Class 3	Class 4	Class 4	Class 4⁽¹⁾	Class 4⁽¹⁾
4-Pair 75W	Class 3	Class 3	Class 4	Class 4	Class 5D	Class 4
4-Pair 90W	Class 3	Class 3	Class 4	Class 4	Class 5D	Class 5D

(1) To ensure IEEE 802.3bt compliance, Type-3 configured PSEs are not permitted to assign more than 30W (Class 4) of power over any individual pairset. Note: Changes were made in the SRAM release v05 to comply with this requirement.

Note:

Class "X-D" Dual Signature PDs present as Class "X" on each alterative pairset. For example: a "Class 4D" PD presents as Class 4 on both the Alterative A and Alternative B pairsets.