Table 3. component manufacturers – Rainbow Electronics MAX5960 User Manual
Page 22
MAX5959/MAX5960
Quad PCI Express, Hot-Plug Controllers
22
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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:
C
LOAD
< (t
SU
x I
LIM
) / V
OUT
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 4µs (typ).
Because some load fault conditions can cause voltage
transients to propagate to the supply inputs with dura-
tion of greater than 4µs, it is recommended that a small
Schottky diode be placed in series with the 12VIN pin
connection, upstream of the 1µF 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