LTC4282 datasheet(23/32 Pages) AD

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LTC4238

Rev. 0

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APPLICATIONS INFORMATION

On-Off Control

The LTC4238 can be configured to turn on automatically

on insertion by connecting the UV/OV resistive voltage

divider through a short pin on the connector. For an active

high turn-on, the top of the divider is connected to the

supply through the short pin as in Figure 8a; for active low

turn-on, the bottom of the divider is connected to ground

through the short pin as in Figure 8b. Both the UV and

OV pins are rated to 100V so no additional protection is

needed when pulled up to the supply.

An open-drain pull-down, or logic level NMOS may be

connected to the UV pin to allow a logic signal to turn the

LTC4238 on and off as shown in Figure 8c.

In addition the COMM pin may be used to turn off the

LTC4238 by pulling it to GND with an open-drain pull-

down. When COMM is released, the LTC4238 will turn on

immediately provided no faults are present.

Parallel Controllers Using the COMM Pin

The LTC4238 has a COMM pin that communicates its sta-

tus so that multiple LTC4238s can operate in parallel. Tie

the COMM pins of a group of parts together to allow them

to operate in tandem. A small capacitor may be connected

to COMM node to improve noise immunity if necessary.

The COMM pin has 4 states.

• Zero Volts mean none of the parts can turn on. Any

part with a fault present will pull the pin to 0V to turn

off the entire bank.

• 0.8V indicates only the start-up channel of the parts

configured with LSSS mode are allowed to turn on.

Those parts will regulate the COMM at 0.8V voltage

with a 5µA pull-up current until the start-up MOSFET

is fully enhanced.

• 2.5V at the COMM indicates that all the parts can turn

on. The parts that have no faults present regulate at

2.5V with a 5µA pull-up current. The parts that are

on and in current limit will disable the 2.5V regulator,

allowing the COMM voltage to rise.

• 5V means all the parts are in current limit.

When configured as a current limit timer, only one

LTC4238 needs to have capacitor connected to the TMR

pin. When the COMM voltage is within 1.5V of INTVCC,

the current limit TMR integrates. The remaining LTC4238s

may have their TMR pins grounded to disable overcurrent

LTC4238

48V

CUV

LTC4238

48V

LTC4238

48V

CUV

100V

OFF

4238 F08

(a) Short Pin to Supply

(b) Short Pin to Ground

Figure 8. On/Off Control with UV/OV Pins

LTC4282 Datasheet(PDF) 23 Page - Analog Devices

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