MAX5971B Maxim Integrated Products, MAX5971B Datasheet - Page 33

• Manufacturer Part Number: MAX5971B
• Description: PSE Controller
• Manufacturer: Maxim Integrated Products

The backoff enable register (R15h, Table 22) is used
to control cadence timing (midspan) for the port. On a
power-up or after a reset condition, this register is set to
a default value of 0000 to 000x where x is the latched in
value of the MIDSPAN input. Setting BCKOFF (R15h[0])
to 1 enables cadence timing where the port backs off and
waits 2.2s (typ) after each failed load detection. The IEEE
802.3af/at standard requires a PSE that delivers power
through the spare pairs (midspan) to have cadence tim-
ing (see the Midspan Mode section for details).
The timing register (R16h, Table 23) is used to program
the restart, startup, overcurrent, and load-disconnect
timers for the port. On a power-up or after a reset con-
dition, the timing register is set to a default value of
00h. To program the timer values, set the bits in R16h
to scale the t
multiple of their nominal value specified in the Electrical
Characteristics table.
Table 22. Backoff Enable Register
Table 23. Timing Register
TSTART[1]
TSTART[0]
TFAULT[1]
TFAULT[0]
SYMBOL
TDISC[1]
TDISC[0]
RSTR[1]
RSTR[0]
SYMBOL
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
BCKOFF
ADDRESS = 16h
ADDRESS = 15h
BIT NO.
DISC
7
6
5
4
3
2
1
0
BIT NO.
______________________________________________________________________________________
, t
7
6
5
4
3
2
1
0
FAULT
Backoff Enable Register (R15h)
TYPE
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
, t
START
TYPE
R/W
Timing Register (R16h)
—
—
—
—
—
—
—
Restart timer programming bit 1
Restart timer programming bit 0
Startup timer programming bit 1
Startup timer programming bit 0
Overcurrent timer programming bit 1
Overcurrent timer programming bit 0
Load-disconnect timer programming bit 1
Load-disconnect timer programming bit 0
Single-Port, 40W, IEEE 802.3af/at,
, and t
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Enable cadence timing on the port
RESTART
to a
PSE Controller with I
TDISC[1:0] (R16h[1:0]) is used to program the load-
disconnect detection time (t
power to the port if it fails to provide a minimum power
maintenance signal for longer than the programmed
load-disconnect detection time. TFAULT[1:0] (R16h[3:2])
programs the overcurrent fault time (t
is the time allowed for the port to remain in an overcur-
rent state both during startup and normal operation
(see the Overcurrent Protection section). TSTART[1:0]
(R16h[5:4]) programs the startup timer (t
time is the time the port is allowed to be in current limit
during startup. RSTR[1:0] programs the discharge rate
of the TFAULT counter (t
the time the port remains off after an overcurrent fault.
When the MAX5971B shuts down a port due to an
extended overcurrent condition (either during startup or
normal operation), if RSTR_EN (R17h[6]) is set high, the
part does not allow the port to power back on before the
restart timer (t
sets a minimum duty cycle that protects the external
MOSFET from overheating during a prolonged output
overcurrent condition.
DESCRIPTION
DESCRIPTION
RESTART
) returns to zero. This effectively
RESTART
DISC
). The device turns off
) and effectively sets
FAULT
START
). Fault time
). Startup
2
C
33