Rainbow Electronics MAX5965B - Manual (Page 35)

MAX5965A/MAX5965B
High-Power, Quad, Monolithic, PSE Controllers
for Power over Ethernet
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Table 20a. Timing Configuration Register
ADDRESS = 16h
SYMBOL BIT R/W
DESCRIPTION
RSTR[1] 7 R/W Restart timer programming bit 1
RSTR[0] 6 R/W Restart timer programming bit 0
TSTART[1] 5 R/W Startup timer programming bit 1
TSTART[0] 4 R/W Startup timer programming bit 0
TFAULT[1] 3 R/W Overcurrent timer programming bit 1
TFAULT[0] 2 R/W Overcurrent timer programming bit 0
TDISC[1] 1 R/W Load disconnect timer programming bit 1
TDISC[0] 0 R/W Load disconnect timer programming bit 0
Table 20b. Startup, Fault, and Load Disconnect Timer Values for Timing Register
BIT [1:0]
(ADDRESS = 16h)
RSTR t DISC t START t FAULT
00 16 x t FAULT t DISC nominal (350ms, typ) t START nominal (60ms, typ) t FAULT nominal (60ms, typ)
01 32 x t FAULT
1/4 x t
DISC nominal 1/2 x t
START nominal 1/2 x t
FAULT nominal
10 64 x t FAULT
1/2 x t
DISC nominal 2 x t START nominal 2 x t FAULT nominal
11 0 x t FAULT 2 x t DISC nominal 4 x t START nominal 4 x t FAULT nominal
TSTART[1,0] (Table 20a) programs the startup timers.
Startup time is the time the port is allowed to be in cur-
rent limit during startup. TFAULT[1,0] programs the
fault time. Fault time is the time allowed for the port to
be in current limit during normal operation. RSTR[1,0]
programs the discharge rate of the TFAULT_ counter
and effectively sets the time the port remains off after
an overcurrent fault. TDISC[1,0] programs the load dis-
connect detection time. The device turns off power to
the port if it fails to provide a minimum power mainte-
nance signal for longer than the load disconnect detec-
tion time (TDISC). Set the bits in R16h to scale the t START , t FAULT , and
t DISC to a multiple of their nominal value specified in the
Electrical Characteristics table.
When the MAX5965A/MAX5965B shut down a port due
to an extended overcurrent condition (either during
startup or normal operation), if RSTR_EN is set high, the
part does not allow the port to power back on before
the restart timer (Table 20b) returns to zero. This effec-
tively sets a minimum duty cycle that protects the exter-
nal MOSFET from overheating during prolonged output
overcurrent conditions. A reset sets R16h = 00h.