LTC4211CS8 datasheet(12/36 Pages) LINER

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LTC4211

4211f

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 dam-

age 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, allow-

ing 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 pre-

determined 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 il-

lustrated in Figure 2. When the supply voltage at the FB pin

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

COMP2 output goes high. After passing through a glitch fil-

ter, RESET is pulled low (Time Point N2). 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 N4). 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 Point N3).

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 operation,

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.

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

OPERATIO

LTC4211CS8 Datasheet(PDF) 12 Page - Linear Technology

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