Rainbow Electronics MAX5958 - Manual (Page 15)

MAX5957/MAX5958
Triple PCI Express, Hot-Plug Controllers
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At power-up, the MAX5957/MAX5958 keep all the
external MOSFETs off until all supplies rise above their
respective UVLO thresholds. These devices keep the
internal MOSFETs off only until the 3.3VAUXIN supply
rises above its UVLO threshold. Upon a turn-on com-
mand, the MAX5957/MAX5958 enhance the external
and internal MOSFETs slowly with a constant gate cur-
rent to limit the power-supply inrush current. The
MAX5957/MAX5958 actively limit the current of all out-
puts at all times and shut down the corresponding
channel if an overcurrent condition persists for longer
than a resistor-programmable overcurrent timeout (see
the
Fault Management section). Thermal protection cir-
cuitry also shuts down all outputs if the die temperature
exceeds +150°C. After an overcurrent or overtempera-
ture fault condition, the MAX5957/MAX5958 latch off or
automatically restart after a restart time delay.
The power requirement for PCIe connectors is defined
by the PCIe card specification and summarized in
Table 1.
Startup
The main supply outputs can become active only after
all the following events have occurred:
• V 3.3AUXIN is above its UVLO threshold.
• V 12VIN and V 3.3SA+ are both above their UVLO
threshold.
• ON_ is driven high.
• PRES-DET_ is low for more than 4ms.
The auxiliary supply output is made available only after
the following events have occurred:
• V 3.3AUXIN is above its UVLO threshold.
• AUXON_ is driven high.
• PRES-DET_ is low for more than 4ms.
The FON_ input overrides all other control signals and
turns on the respective slot when driven low, as long as
the UVLO thresholds have been reached. Table 2 sum-
marizes the logic conditions required for startup. The aux-
iliary supply input powers the internal control logic and
analog references of the MAX5957/MAX5958, so the main
supplies cannot be enabled, if V
3.3VAUXIN is not present.
When an output is enabled, a programmable startup
timer (t
SU ) begins to count the startup time duration.
The value of t SU is set to 2x the fault timeout period
(t
FAULT
). R
TIM
externally connected from TIM to GND
sets the duration of t
FAULT
.
Table 1. Power Requirement for PCIe Connectors
POWER FAIL X1 CONNECTOR X4/8 CONNECTOR X16 CONNECTOR
3.3V
Voltage Tolerance ±9% (max) ±9% (max) ±9% (max)
Supply Current 3.0A (max) 3.0A (max) 3.0A (max)
Capacitive Load 1000µF (max) 1000µF (max) 1000µF (max)
12V
Voltage Tolerance ±8% (max) ±8% (max) ±8% (max)
Supply Current 0.5A (max) 0.5A (max) 0.5A (max)
Capacitive Load 300µF (max) 1000µF (max) 2000µF (max)
3.3V AUXILIARY
Voltage Tolerance ±9% (max) ±9% (max) ±9% (max)
Supply Current, Wake Enabled 375mA (max) 375mA (max) 375mA (max)
Supply Current, Nonwake Enabled 20mA (max) 20mA (max) 20mA (max)
Capacitive Load 150µF (max) 150µF (max) 150µF (max)