MAX5960AECS+T【PDF 22/25 页】IC CTRLR HOT-PLUG QD 80-TQFP

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Quad PCI Express, Hot-Plug Controllers

22 ______________________________________________________________________________________

Additional External Gate Capacitance

External capacitance can be added from the gate of

the external MOSFETs to GND to slow down the dV/dt

of the 12V and 3.3V outputs. The maximum gate

capacitance load at 12G_ and 3.3G_ must be consis-

tent with the conditions described in the Setting the

Power-On Reset section.

Maximum Load Capacitance

Large capacitive loads at the 12V output, the 3.3V out-

put, and the 3.3V auxiliary output can cause a problem

when inserting discharged PCI cards into live back-

planes. A fault occurs if the time needed to charge the

capacitance of the board is greater than the typical

startup time (2 x t

FAULT

). The MAX5959/MAX5960 with-

stand large capacitive loads due to their adjustable

startup times and adjustable current-limit thresholds.

Calculate the maximum load capacitance as follows:

LOAD

< (t

x I

LIM

) / V

OUT

is either the 3.3V output, the 12V output, or the

3.3V auxiliary output for slot A, slot B, slot C, or slot D.

Input Transients

The 12V input (12VIN), the 3.3V input (3.3SA+), and the

3.3V auxiliary (3.3AUXIN) must be above their UVLO

thresholds before startup can occur. Input transients

can cause the input voltage to sag below the UVLO

threshold. The MAX5959/MAX5960 reject transients on

the input supplies that are shorter than 4祍 (typ).

Because some load fault conditions can cause voltage

transients to propagate to the supply inputs with dura-

tion of greater than 4祍, it is recommended that a small

Schottky diode be placed in series with the 12VIN pin

connection, upstream of the 1礔 bypass capacitor. This

provides a hold-up supply that will prevent the 12VIN

input from dropping below V

12UVLO

during severe tran-

sients. See the Typical Application Circuit.

Table 3. Component Manufacturers

COMPONENT

MANUFACTURER

PHONE

WEBSITE

Vishay-Date

402-564-3131

www.vishay.com

Sense Resistor

IRC

704-264-8861

www.irctt.com

Fairchild

888-522-5372

www.fairchildsemi.com

International Rectifier

310-322-3331

www.irf.com

Motorola

602-244-3576

www.mot-sps.com/ppd

MOSFETs

Vishay-Siliconix

www.vishay.com

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