MAX5960AECS+T【PDF 19/25 页】IC CTRLR HOT-PLUG QD 80-TQFP

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Sheet目录43

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Quad PCI Express, Hot-Plug Controllers

______________________________________________________________________________________ 19

Debounced Logic Gate

(INPUT_ and OUTPUT_)

INPUT1, INPUT2, and INPUT3 accept inputs from

mechanical switches. The corresponding outputs are

OUTPUT1, OUTPUT2, OUTPUT3, and OUTPUT4. OUT-

PUT_ is debounced for 4ms. When INPUT_ goes from

high to low, OUTPUT_ goes low immediately and stays

low for at least 4ms. After the debounce time, OUT-

PUT_ follows INPUT_. If INPUT_ goes from low to high,

OUTPUT_ goes high immediately and stays high for at

least 4ms. After the debounce time, OUTPUT_ follows

INPUT_. Figure 5 shows the timing diagram describing

the INPUT_/OUTPUT_ debounced feature.

Present-Detect and Forced-On Inputs

(PRES-DET_, FON_)

PRES-DET_ input detects the PRSNT_# pin on a PCIe

connector. When the card is plugged in, PRES-DET_

goes low and allows the turn-on of the outputs of the

respective slot after a 4ms debounced time. When the

card is removed, an internal 50k?pullup resistor forces

PRES-DET_ high and the respective slot is shut down

with no delay. PRES-DET_ works in conjunction with

ON_ and AUXON_ and only enables the device when

ON_ and AUXON_ are high.

A logic-low on FON_ forces the respective slot (main

supplies and auxiliary) to turn on regardless of the sta-

tus of the other logic inputs, provided the UVLO thresh-

olds are exceeded on all the inputs.

Active Current Limits

Active current limits are provided for all three outputs of

the four slots (slot A, slot B, slot C, and slot D). Connect

a current-sense resistor between 12S_+ and 12S_- to

set the current limit for the 12V outputs. The current

limit is set to 54mV / R

SENSE12

. Connect a current-

sense resistor between 3.3S_+ and 3.3S_- to set the

current limit for the 3.3V main outputs to 20mV /

SENSE3.3

. For the auxiliary output (3.3VAUXO_) the

current limit is fixed at 450mA in the MAX5959 and

700mA in the case of the MAX5960.

When the voltage across R

SENSE12

or R

SENSE3.3

reaches the current-limit threshold voltage, the

MAX5959/MAX5960 regulate the gate voltage to main-

tain the current-limit threshold voltage across the sense

resistor. If the current limit lasts for t

FAULT

, then an

overcurrent fault occurs. The MAX5959/MAX5960 shut

down both the 12V and 3.3V outputs and assert the

FAULT_ output of the respective slot.

When the auxiliary output reaches the current limit 450mA

(MAX5959) or 700mA (MAX5960) for longer than t

FAULT

, a

fault occurs and the device shuts down all outputs and

asserts FAULT of the respective slot.

UVLO Threshold

The UVLO thresholds prevent the internal auxiliary

MOSFETs and the external main channel MOSFETs

from turning on if V

12VIN

, V

3.3VIN

, and V

3.3VAUXIN

are

not present. Internal comparators monitor the main

supplies and the auxiliary supply and keep the gate-

drive outputs (12GA, 12GB, 12GC, 12GD, 3.3GA,

3.3GB, 3.3GC, and 3.3GD) low until the supplies rise

above their UVLO threshold. The 12V main supply is

monitored at 12VIN and has a UVLO threshold of 10V.

The 3.3V main supply is monitored at 3.3SA+ and has

a UVLO threshold of 2.65V. The auxiliary supply is

monitored at 3.3AUXIN and has a 2.65V UVLO thresh-

old. For either main channels to operate, V3.3AUXIN

must be above its UVLO threshold.

Figure 5. INPUT_ AND OUTPUT_ Debounced Feature

INPUT

DEBOUNCED

OUTPUT

DBC

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