Rainbow Electronics MAX5960 - Manual (Page 18)

MAX5959/MAX5960
Quad PCI Express, Hot-Plug Controllers
18 ______________________________________________________________________________________
12V and 3.3V Outputs Normal Operation
The MAX5959/MAX5960 monitor and actively limit the
current of the 12V and 3.3V outputs after the startup
period. Each output has its own overcurrent threshold.
If any of the monitored output currents rise above the
overcurrent threshold for a period t
FAULT , FAULT_
asserts and the controller disengages both the 12V and
3.3V outputs for the particular slot (see the
Fault
Management section).
3.3V Auxiliary Output Normal Operation
The auxiliary output current is internally monitored and
actively limited to the maximum current-limit value. An
overcurrent fault condition occurs when the output cur-
rent exceeds the overcurrent threshold for longer than
t
FAULT . A fault on an auxiliary channel causes all sup-
plies of the affected channel to be disabled after a pro-
grammable time period t
FAULT .
A fault condition on a main channel (V 12VIN or V 3.3VIN )
causes all the channel’s main outputs to shut down
after the t
FAULT period and then either latch off or auto-
matically restart after the t RESTART (t RESTART = 64 x
t
FAUALT
) period, depending on the device version. A
fault on any of the channel’s main output does not
affect the auxiliary channel (V
3.3AUXIN ).
Power-Good (PWRGD_)
Power-good ( PWRGD_) is an open-drain output that
pulls low a time (t
POR_HL
) after all the outputs of the
respective slot are fully on. All outputs are considered
fully on when 3.3G_ has risen to V
PGTH3.3 , 12G_ has
risen to V PGTH12 , and V 3.3AUXO_ is less than
V PGTH3.3AUX . t POR_HL is adjustable from 2.4ms to 1.5s
by connecting a resistor from PORADJ to GND. See the
Setting the Power-On Reset and Timeout Period
(t POR_HL ) sections. Connect PORADJ to GND to com-
pletely skip the POR time delay for PWRGD_ assertion.
Thermal Shutdown
When the die temperature goes above (T SD ) +150°C, an
overtemperature fault occurs and the MAX5959/
MAX5960 shut down all outputs. The device waits for the
junction temperature to decrease below T
SD - hysteresis
before entering fault management (see the Fault
Management section):
Fault Management
A fault occurs when an overcurrent or 12G_ or 3.3G_
below their power-good threshold lasts longer than
t
FAULT or when the device experiences an overtemper-
ature condition:
• A fault on a main output (12V or 3.3V) shuts down
both main outputs of the respective slot. The 3.3V
auxiliary is not affected.
• A fault on the 3.3V auxiliary output shuts down all
three outputs of the respective slot.
The MAX5959A/MAX5960A automatically restart from a
fault shutdown after the t
RESTART period while the
MAX5959L/MAX5960L latch off. If an overcurrent fault
occurred on a main output, bring ON_ low for at least
t
RESET (100µs) and high again to reset the fault and
restart the outputs. If the overcurrent fault occurred on
an auxiliary output or an overtemperature fault
occurred, bring both ON_ and AUXON_ low for a mini-
mum of t
RESET to reset the fault. Toggle ON_ or only
AUXON_ to reset the fault condition. If ON_ and
AUXON are toggled before t
RESTART time counting has
elapsed, the MAX5959L/MAX5960L store the informa-
tion and restart when the delay is finished. The
MAX5959A/MAX5960A (autoretry versions) restart all
channels automatically after t
RESTART .
Figure 4. 12 Output Overcurrent/Short Circuit During Normal
Operation
FAULT_
PWRGD_ IS PULLED UP TO 3.3VAUXO_.
FAULT_ IS PULLED UP TO 3.3VAUXIN.
A FAULT ON THE 3.3V OUTPUT OR 3.3VAUXO_ OUTPUT PRODUCES SIMILAR RESULTS.
t FAULT
PWRGD_
12G_
12V OUTPUT
CURRENT
V 12ILIM,TH
R SENSE