LM9070

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SNVS130E – DECEMBER 1999 – REVISED APRIL 2013

APPLICATION INFORMATION

The LM9070 voltage regulator has been optimized for use in microprocessor based automotive systems. Several

unique design features have been incorporated to address many FMEA (Failure Mode Effects Analysis) concerns

for fail-safe system performance.

FAULT TOLERANT FEATURES

While not specifically ensured due to production testing limitations, the LM9070 has been tested and shown to

continue to provide a regulated output and, not generate an erroneous system reset signal while subjected to

high levels of RF electric field energy (up to 300 V/m signal strength over a 2 MHz to 400 MHz frequency range).

This is very important in vehicle safety related applications where the system must continue to operate normally.

To maintain this immunity to RFI the output bypass capacitor is important (47

μF is recommended).

This regulator is suitable for applications where continuous connection to the battery is required (Refer to the

Figure 21). ON/OFF control of the regulator and system can be accomplished by switching the ON/OFF input to

pull-down resistor ensures that the regulator turns OFF. When the regulator is switched OFF the current load on

the battery drops to less than 60

to be connected in a system through long lengths of wire, the ESD protection of these pins has been increased

to 12 kV with the addition of small input bypass capacitors.

Figure 21. Typical Application Circuit

An output bypass capacitor of at least 10

μF is required for stability (47 μF is recommended). The ESR of this

capacitor should be less than 3

Ω. An input capacitor of 1 μF or larger is recommended to improve line transient

and noise performance.

With the Keep-Alive input, a system microprocessor has the ability to keep the regulator ON (with a logic “0” on

Keep-Alive) after the ON/OFF input has been commanded OFF. A power-down sequence, when system

variables are typically stored in programmable memory, can be executed and take as much time as necessary.

At the end of the operation the micro then pulls Keep-Alive high and the regulator and system turn OFF and

revert to the low quiescent current standby mode.

For additional system reliability, consideration has been made for the possibility of a short circuited load at the

output of the regulator. When the regulator is switched ON, conventional current limiting and thermal shutdown

the shorted regulator output) will force the Keep-Alive input to be low and thus try to maintain the Keep-Alive

mode of operation. With a shorted load, the drain on the battery could be as high as 1.5A. A separate internal

load, the Keep-Alive function is logically disabled to ensure that the regulator turns OFF and reverts to only a 50

μA load on the battery.

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