Application Information

PIN DESCRIPTION AND FUNCTIONALITY

The LM9072 is a precision dual tracking voltage regulator

optimized for use in powertrain module applications but will

also find use in a wide variety of automotive and industrial

applications where precision supply regulation is required in

harsh operating environments. The following will describe

the functionality of each of the package pins.

INPUT VOLTAGE (Pin 3)

The LM9072 has been designed to connect directly to the ig-

nition or battery supply in automotive applications. For this

type of supply the regulator has been designed to withstand

up to +60V and −45V supply transients such as load dump.

An overvoltage shut down protection scheme turns OFF

both of the regulator outputs should supply transients ex-

ceed typically +33V to fully protect all load circuitry. This

higher threshold allows normal operation with 24 V

plied to the input as in the event when two batteries are used

to start a vehicle. Protection of the system is also provided

for inadvertent reverse polarity battery connections.

The current drain on the supply line is directly proportional to

the load currents on the two voltage regulators. With no load

current on either output the regulator requires 15 mA maxi-

mum quiescent current for biasing internal circuitry. During

dropout conditions (V

can rise to 50% of the total load current. With less than 4V

applied to the input, internal biasing circuitry shuts OFF.

When

switched OFF the regulator can remain connected to

the battery supply with a current drain of less than 100 µA.

MAIN OUTPUT (Pin 9)

The Main Output regulator provides a well controlled (3% tol-

erance maximum) 5V supply line with a total load current

ranging up to 350 mA. This relatively high level of output cur-

rent is sufficient to provide power to a large number of load

circuits in a variety of module applications.

This output has a short to ground current limit between

500 mA and 1A. The Main output can also withstand a short

circuit to potentials up to 7V.

To maintain stability of this supply line an output bypass ca-

pacitor is required. This capacitor must be at least 6 µF with

an equivalent series resistance (ESR) between 0.3

Ω and 3Ω

over temperature.

The Main Output is sensed for the generation of the system

reset output. Feedback from the Main Output is also used to

control the output voltage of the tracking regulator.

TRACKING OUTPUT (Pin 4)

The Tracking Output regulator is a key feature of the

LM9072. This output provides a voltage that directly tracks

the main output voltage within 1.5%. This 80 mA output is

provided to bias sensors and other devices located external

to the main system module.

For providing remote power the Tracking Output is fully pro-

tected against short circuit connections to the battery or input

supply (up to 27V) and to ground. These shorted fault condi-

tions do not affect the operation of the main supply nor gen-

erate a reset of the system.

The tracking characteristic allows for ratiometric operation of

sensors by providing power that is directly proportional to the

system supply. Similar to the main output a bypass capacitor

is required for stability. This capacitor should also be greater

than 6 µF with an ESR between 0.3

Ω and 3Ω.

DS012906-17

FIGURE 1. Circuit Block Diagram

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