Rainbow Electronics MAX5960 - Manual (Page 19)

MAX5959/MAX5960
Quad PCI Express, Hot-Plug Controllers
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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 50kΩ 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 /
R
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
t
DBC
t
DBC
t
DBC