LTC4244IGN datasheet(11/28 Pages) LINER

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LTC4244/LTC4244-1

42441f

APPLICATIO S I FOR ATIO

Hot Circuit Insertion

When a circuit board is inserted into a live CompactPCI

(CPCI) bus, the supply bypass capacitors can draw huge

inrush currents from the CPCI power bus as they charge

up. These transient currents can create glitches on the

power bus, causing other boards in the system to reset.

The LTC4244 is designed to turn a board’s back-end

supply voltages on and off in a controlled manner, allow-

ing the board to be safely inserted or removed from a live

CPCI connector without glitching the system power sup-

plies. It also protects the system supplies from shorts,

precharges the bus I/O connector pins during hot insertion

and extraction, and monitors the supply voltages.

The LTC4244 is specifically designed for CPCI applica-

tions where the Hot Swap controller resides on the plug-

in board.

LTC4244 Feature Summary

• Allows safe insertion and removal from a CPCI back-

plane.

• Controls all four CPCI supplies: -12V, 12V, 3.3V and 5V.

• Adjustable foldback current limit for the 5V and 3.3V

supplies: an adjustable analog current limit with a value

that depends on the output voltage. If the output is

shorted to ground the current limit drops to keep power

dissipation and supply glitches to a minimum.

• 12V and –12V circuit breakers: if either supply remains

in analog foldback current limit for more than 25

µs, the

circuit breakers will trip, the supplies are turned off and

the FAULT pin is pulled low.

• Adjustable 5V and 3.3V circuit breakers: if either supply

exceeds its current limit for more than 25

µs, the circuit

breaker will trip, the supplies will be turned off and the

FAULT pin is asserted low. In the event of a short circuit

on either supply, an analog current limit will prevent the

supply current from exceeding three times the circuit

breaker threshold current.

• Current limit during power up: the supplies are allowed

to power up in current limit. This allows the LTC4244 to

power up boards with widely varying capacitive loads

without tripping the circuit breaker. The maximum

allowable power-up time is adjustable using the TIMER

pin capacitor.

• Internal 12V and –12V power switches.

• PWRGD output: monitors the voltage status of the four

back-end supply voltages.

• PCI_RST# combined on chip with HEALTHY# to create

LOCAL_PCI_RST# output. Simply connect the

PCI_RST# signal to the RESETIN pin and the

LOCAL_PCI_RST# signal to the open-drain RESETOUT

pin.

• Precharge output: on-chip reference and error amplifier

provide 1V for biasing bus I/O connector pins during

CPCI card insertion and extraction.

• TIMER/AUX. VCC: After power-up, the TIMER pin ca-

pacitor serves as auxiliary VCC, thus enabling the

LTC4244 to ride out large voltage spikes on the 12VIN

supply without interruption.

• Undervoltage lockout: All four input voltages are pro-

tected by undervoltage lockouts.

• Space saving 20-pin SSOP package.

LTC4244 vs LTC1644

The LTC4244 is pin-for-pin compatible with the LTC1644.

There are, however, some important differences between

the two parts:

• TIMER: The LTC4244’s TIMER pin threshold voltage is

1.6V below V12VIN vs 1V for the LTC1644. After power-

up, the LTC4244’s TIMER pin also doubles as auxiliary

VCC.

•VEEIN UVL: The LTC4244 has a –9.5V UVL threshold

protecting the VEEIN supply. The LTC1644 has no VEEIN

UVL feature.

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