The MAX5946 dual hot-plug controller is designed for
PCI Express® applications. The device provides hotplug
control for 12V, 3.3V, and 3.3V auxiliary supplies of
two PCI Express slots. The MAX5946's logic inputs/outputs
allow interfacing directly with the system hot-plug
management controller or through an SMBus™ with an
external I/O expander. An integrated debounced attention
switch and present-detect signals are included to
simplify system design.
The MAX5946 drives four external n-channel MOSFETs
to control the 12V and 3.3V main outputs. The 3.3V auxiliary
outputs are controlled through internal 0.3Ω
n-channel MOSFETs. Internal charge pumps provide
gate drive for the 12V outputs while the gate drive of
the 3.3V output is driven by the 12V input supply. The
3.3V auxiliary outputs are completely independent from
the main outputs with their own charge pumps.
At power-up, the MAX5946 keeps all of the external
MOSFETs off until the supplies rise above their respective
undervoltage lockout (UVLO) thresholds. The
device keeps the internal MOSFETs off only until the
auxiliary input supply rises above its UVLO threshold.
Upon a turn-on command, the MAX5946 enhances the
external and internal MOSFETs slowly with a constant
gate current to limit the power-supply inrush current.
The MAX5946 actively limits the current of all outputs at
all times and shuts down if an overcurrent condition
persists for longer than a programmable overcurrent
timeout. Thermal-protection circuitry also shuts down all
outputs if the die temperature exceeds +150°C. After an
overcurrent or overtemperature fault condition, the
MAX5946L latches off while the MAX5946A automatically
restarts after a restart time delay. The device is available
in a 36-pin (6mm x 6mm) thin QFN package and
operates over the -40°C to +85°C temperature range.
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