LTC1421 datasheet(13/40 Pages) LINER

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LTC4211

4211fb

OPERATION

SENSE

RSENSE

10k

VCC

VOUT

GATE

LTC4211

GND

4211 F01

RESET

CTIMER

TIMER

CLOAD

LOGIC

TIMER

1.236V

REFERENCE

COMP2

μP

RESET

SHORT

LONG

VCC

ON/RESET

GND

LONG

PCB EDGE

CONNECTOR

(MALE)

BACKPLANE

CONNECTOR

(FEMALE)

–

VOUT

TIMER

RESET

1.236V

POWER GOOD

DELAY

4211 F02

Figure 1. Supply Voltage Monitor Block Diagram

Figure 2. Supply Monitor Waveforms in Normal Mode

HOT CIRCUIT INSERTION

When circuit boards are inserted into or removed from

live backplanes, the supply bypass capacitors can draw

huge transient currents from the backplane power bus as

they charge. The transient current can cause permanent

damage to the connector pins as well as cause glitches

on the system supply, causing other boards in the system

to reset.

The LTC4211 is designed to turn a printed circuit board’s

supply voltages ON and OFF in a controlled manner, al-

lowing the circuit board to be safely inserted or removed

from a live backplane. The device provides a system

reset signal to indicate when board supply voltage drops

below a predetermined level, as well as a dual function

fault monitor.

OUTPUT VOLTAGE MONITOR

The LTC4211 uses a 1.236V bandgap reference, precision

voltage comparator and an external resistor divider to

monitor the output supply voltage as shown in Figure 1.

The operation of the supply monitor in normal mode is

illustrated in Figure 2. When the voltage at the FB pin

drops below its reset threshold (1.236V), the comparator

COMP2 output goes high. After a glitch filter delay, RESET

is pulled low (Time Point 1). When the voltage at the FB

pin rises above its reset threshold (1.239V), COMP2’s

output goes low and a timing cycle starts (Time Point 4).

After a complete timing cycle, RESET is pulled high by

the external pull-up resistor. If the FB pin rises above the

reset threshold for less than a timing cycle, the RESET

output remains low (Time Points 2 to 3).

As shown in Figure 5, the LTC4211’s RESET pin is logic

low during any undervoltage lockout condition and during

the initial insertion of a PC board. Under normal opera-

tion, RESET goes to logic high at the end of the soft-start

cycle only after the FB pin voltage rises above its reset

threshold of 1.239V.

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