LTC1645CS datasheet(7/24 Pages) LINER

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LTC1645

Hot Circuit Insertion

When a circuit board is inserted into a live backplane, the

supply bypass capacitors on the board can draw huge

transient currents from the backplane power bus as they

charge. These transient currents can cause permanent

damage to the connector pins and produce glitches on the

system supply, resetting other boards in the system.

The LTC1645 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 backplane. The chip

provides a system reset signal and a spare comparator to

indicate when board supply voltages drop below user-

programmable voltages, and a fault signal to indicate if an

overcurrent condition has occurred.

The LTC1645 can be located before or after the connector

as shown in Figure 1. A staggered PCB connector can

sequence pin connections when plugging and unplugging

circuit boards. Alternatively, the control signal can be

generated by processor control.

Power Supply Tracking and Sequencing

Some applications require that the potential difference

between two power supplies not exceed a certain voltage.

This requirement applies during power-up and power-

down as well as during steady state operation, often to

prevent latch-up in a dual supply ASIC. Other systems

require one supply to come up after another, for example,

if a system clock needs to start before a block of logic.

Typical dual supplies or backplane connections may come

up at arbitrary rates depending on load current, capacitor

size, soft-start rates, etc. Traditional solutions are cum-

bersome and require complex circuitry to meet the power

supply requirements.

The LTC1645 provides a simple solution to power supply

tracking and sequencing needs. The LTC1645 guarantees

supply tracking by ramping the supplies up and down

together (see Figure 15). The sequencing capabilities of

the LTC1645 allow nearly any combination of supply

ramping (e.g., see Figure 17) to satisfy various sequenc-

ing specifications. See the Power Supply Tracking and

Sequencing Applications section for more information.

APPLICATIO S I FOR ATIO

SENSE

FAULT

VCC

VOUT

FAULT

GND

GATE

LTC1645

BACKPLANE

CONNECTOR

STAGGERED PCB

EDGE CONNECTOR

CLOAD

VCC

(a) Hot Swap Controller on Motherboard

SENSE

FAULT

VCC

VOUT

FAULT

GND

GATE

LTC1645

1645 F01

CLOAD

VCC

BACKPLANE

CONNECTOR

STAGGERED PCB

EDGE CONNECTOR

(b) Hot Swap Controller on Daughterboard

Figure 1. Staggered Pins Connection

LTC1645CS Datasheet(PDF) 7 Page - Linear Technology

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