LTC4240IGN datasheet(11/28 Pages) LINER

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LTC4240

4240f

The LTC4240 is a Hot Swap controller that allows a board

to be safely inserted and removed from a CompactPCI bus

slot. The LTC4240 has built-in 2-wire I2C compatible

interface hardware to allow software control and monitor-

ing of device function and power supply status.

Hot Circuit Insertion

When a circuit board is inserted into a live CompactPCI

(CPCI) backplane slot, supply bypass capacitors on the

board can draw huge supply transient currents from the

CPCI backplane power bus. The transient currents can

cause glitches on the power bus, thus causing other

boards in the system to reset.

The LTC4240 is designed to turn a board’s supply voltages

on and off in a controlled manner, allowing the board to be

safely inserted or removed from a live CPCI slot without

disturbing the system power supplies. The device also

protects the supplies from shorts, precharges the bus I/O

pins during insertion and extraction and monitors the

supply voltages. The LTC4240 includes an I2C compatible

interface, which allows software control of device func-

tions.

The LTC4240 is specifically designed for CPCI applica-

tions where it resides on the plug-in board. For best

results, a well bypassed backplane is recommended.

LTC4240 Feature Summary

• Allows safe board insertion and removal from a CPCI

backplane. Status LED visually identifies when a board

is ready for removal.

• Controls all four CPCI supplies: –12V, 12V, 3.3V and

5V.

• Foldback current limit: An 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 current limit for more than 35

µs, the circuit breaker

will trip, the supplies will turn off and the FAULT pin

pulls low.

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

exceeds current limit for more than 35

µs, the circuit

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

FAULT pin will be pulled low. In addition, an analog loop

will servo the GATE pin to limit the current to three times

circuit breaker limit during transient conditions.

•I2C interface: software control allows user to both write

to and read from the device. The user can turn the

device off and on, set the status LED, set RESETOUT

and disable faults on 12VIN and VEEIN. The user can also

read the device status: FAULT, RESETIN, RESETOUT

PWRGD, PRSNT1#, PRSNT2#, FAULTCODE0 and

FAULTCODE1. If a fault occurs, the FAULTCODE bits

identify which supply generated the fault.

• Current limit during power-up: the supplies are allowed

to power-up in current limit. This allows the LTC4240 to

power-up boards with widely varying capacitive loads

without tripping the circuit breaker. The maximum

allowable power-up time is programmable using an

external capacitor connected to the TIMER pin. See

TIMER section

• Internal 12V and –12V power switches.

• PWRGD output: indicates the voltage status of the four

supply voltages.

• PCI_RST# is combined with HEALTHY# and

with the I2C RESETIN latch output to create

LOCAL_PCI_RST# output. If HEALTHY# asserts,

LOCAL_PCI_RST# is asserted independent of the other

two inputs.

• Precharge output: an internal reference and amplifier

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

CPCI card insertion and extraction.

• Space saving 28-pin SSOP package.

I2C Interface

The LTC4240 incorporates an I2C compatible 2-wire (clock

and data) interface that allows the user to easily query and

control the status of the LTC4240. A single analog input

pin selects 1 of 32 allowed addresses. The I2C bus can be

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