MAX5954LETX+T Maxim Integrated Products, MAX5954LETX+T Datasheet - Page 17

• Manufacturer Part Number: MAX5954LETX+T
• Description: IC PCI EXP/HOT-PLUG CTRLR 36TQFN
• Manufacturer: Maxim Integrated Products
• Type: Hot-Swap Controllerr

Specifications of MAX5954LETX+T

• Applications: General Purpose, PCI Express
• Internal Switch(s): No
• Voltage - Supply: 3.3V, 12V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-WFQFN Exposed Pad
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Single PCI Express, Hot-Plug
Controller
stays high for at least 4ms. After the debounce time,
OUTPUT follows INPUT. Figure 5 shows the timing dia-
gram describing the INPUT/OUTPUT debounced feature.
PRES-DET input detects the PRSNT#2 pin on a PCI
Express connector. When the card is plugged in,
PRES-DET goes low and allows the turn-on of the out-
put after a 4ms debounced time. When the card is
removed, an internal 50kΩ pullup forces PRES-DET
high and the PCI Express 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 PCI Express 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 of the inputs.
Active current limits are provided for all three outputs.
Connect a current-sense resistor between 12S+ and
12S- to set the current limit for the 12V output. The cur-
rent limit is set to 54mV/R
current-sense resistor between 3.3S+ and 3.3S- to
set the current limit for the 3.3V main output to
20mV/R
the current limit is fixed at 470mA.
When the voltage across R
reaches the current-limit threshold voltage, the
MAX5954 regulates the gate voltage to maintain the
current-limit threshold voltage across the sense resis-
tor. If the current limit lasts for t
rent fault occurs. The MAX5954 shuts down both the
12V and 3.3V outputs and asserts the FAULT output.
When the auxiliary output reaches the current limit
(470mA) for longer than t
device shuts down all outputs and asserts FAULT.
Figure 5. INPUT and OUTPUT Debounced Feature
DEBOUNCED
OUTPUT
INPUT
Present-Detect and Forced-On Inputs
SENSE3.3.
t
DBC
______________________________________________________________________________________
For the auxiliary output (3.3V
FAULT
Active Current Limits
t
DBC
SENSE12
FAULT
, a fault occurs and the
SENSE12
( P P R R E E S S - - D D E E T T , , F F O O N N )
, then an overcur-
t
DBC
or R
. Connect a
SENSE3.3
AUXO
)
The UVLO thresholds prevent the internal auxiliary
MOSFET and the external main channel MOSFETs (Q1
and Q2 in the Typical Application Circuit) from turning
on if V
Internal comparators monitor the main supplies and the
auxiliary supply and keep the gate-drive outputs (12G
and 3.3G) 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 sup-
ply is monitored at 3.3S+ and has a UVLO threshold of
2.65V. The auxiliary supply is monitored at 3.3VAUXIN
and has a 2.65V UVLO threshold. For the main outputs to
operate, V
The gate drive for the external MOSFETs is provided at
12G and 3.3G. 12G is the gate drive for the 12V main
supply and is boosted to 5.3V above V
internal charge pump. During turn-on, 12G sources
5µA into the external gate capacitance to control the
turn-on time of the external MOSFET. During turn-off,
12G sinks 150µA from the external gate capacitance to
quickly turn off the external MOSFET. During short-cir-
cuit events, an internal 120mA current activates to
rapidly bring the load current into the regulation limits.
3.3G is the gate drive for the 3.3V main supply’s
MOSFET and is driven to 5.5V above the 3.3V main sup-
ply. The power for 3.3G is supplied from 12VIN and has
no internal charge pump. During turn-on, 3.3G sources
5µA into the external gate capacitance to control the
turn-on time of the external MOSFET. During turn-off,
3.3G sinks 150µA to quickly turn off the external
MOSFET. During short-circuit events, an internal 150mA
current activates to rapidly turn off the external
MOSFET.
3.3VAUXIN provides power to the auxiliary output as
well as the internal logic and references. The drain of the
internal auxiliary MOSFET connects to 3.3VAUXIN
through internal sense resistor and the source connects
to the auxiliary output 3.3VAUXO. The MOSFET’s typical
on-resistance is 0.3Ω. An internal charge pump boosts
the gate-drive voltage to fully turn on the internal n-chan-
nel MOSFET. The auxiliary supply has an internal current
limit set to 470mA.
12VIN
3.3VAUXIN
, V
Undervoltage-Lockout Threshold
3.3VIN
External MOSFET Gate Driver
Auxiliary Supply (3.3VAUXIN)
must be above its UVLO threshold.
, and V
3.3VAUXIN
(12G and 3.3G)
are not present.
12VIN
by an
17