MAX5946LETX+T【PDF 13/23 页】IC CNTRLR PCI EXP DL 36TQFN

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Detailed Description

The MAX5946 dual hot-plug controller is designed for

PCI express applications. The device provides hot-plug

control for 12V, 3.3V, and 3.3V auxiliary supplies of two

PCI express slots. The MAX5946s logic inputs/outputs

allow interfacing directly with the system hot-plug-man-

agement controller or through an SMBus with an exter-

nal I/O expander. An integrated debounced attention

switch and present-detect signals are included to sim-

plify system design.

The MAX5946 drives four external n-channel MOSFETs

to control the 12V and 3.3V main outputs. The 3.3V aux-

iliary outputs are controlled through internal 0.24& n-

channel MOSFETs. Internal charge pumps provide a

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 all supplies rise above their respec-

tive UVLO thresholds. The device keeps the internal

MOSFETs off only until the 3.3VAUXIN 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癈. After an overcurrent or

overtemperature fault condition, the MAX5946L latches

off while the MAX5946A automatically restarts after a

restart time delay.

The power requirement for PCI express connectors is

defined by the PCI express card specification and

summarized in Table 1.

Dual PCI Express, Hot-Plug

Controller

______________________________________________________________________________________ 13

NAME

FUNCTION

3.3SB-

Slot B 3.3V Negative Current-Sense Input. See 3.3SA- function.

3.3SB+

Slot B 3.3V Positive Current-Sense Input. Connect the positive side of the current-sense resistor to

3.3SB+ using the Kelvin-sensing technique to assure accurate current sensing.

12GB

Slot B 12V Gate-Drive Output. See 12GA function.

12SB-

Slot B 12V Negative Current-Sense Input. See 12SA- function.

12SB+

Slot B 12V Positive Current-Sense Input. See 12SA+ function.

AUXONB

Slot B 3.3V Auxiliary Output Enable. See AUXONA function.

ONB

Slot B 12V And 3.3V Outputs Enable. See ONA function.

FONB

Slot B Forced-On Input. See FONA function.

PRES-DETB Slot B Present-Detect Input. See PRES-DETA function.

TIM

v r rr n Tim

Pr r mmin In . nn

r i r

w n

& n

k& fr m TIM

to program t

FAULT

. Leave TIM floating for a default timeout of 11ms.

INPUT2

Digital Logic Gate Input

OUTPUT2

Digital Output. 4ms debounced digital output of INPUT2.

OUTPUT1

Digital Output. 4ms debounced digital output of INPUT1.

INPUT1

Digital Logic Gate Input

12VIN

12V Supply Input. V

12VIN

drives the gates of the MOSFETs connected to 3.3GA and 3.3GB. 12VIN

powers an internal charge pump that drives the gates of the MOSFETs connected to 12GA and 12GB.

GND

Ground

PGND

Power Ground. Connect externally to GND.

PORADJ

Power-On-Reset Programming Input. Connect a resistor between 500& and 500k& from PORADJ to

GND to ro ram the POR timin . Leave floatin for a default value of 160ms.

Pin Description (continued)

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