LM9073 datasheet(10/18 Pages) NSC

10 / 18 page

Application Information (Continued)

ranging up to 700mA. 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

900mA and 2A. It is not protected for shorts to battery how-

ever, but can withstand an output short to a potential of 7

Volts or less.

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

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

External Supply Output (pin 5)

The External Supply Output regulator is a secondary 5V, 2%

tolerance regulated output of the LM9073. this 100mA output

is available to bias sensors and other devices located exter-

nal to the main system module.

For providing remote power the External Supply Output is

fully protected against short circuit connections to the battery

or input supply (up to 27V) and to ground. These shorted

fault conditions do not effect the operation of the main supply

nor generate a reset of the system.

Like the main output a bypass capacitor is required for stabil-

ity. This capacitor should be also greater than 6µF with an

ESR between 0.3

Ω and 3Ω.

Reset Output (pin 7)

The Reset Output is an active low logic signal provided to re-

set a system mircocontroller on power up and in the event

that the Main Output falls out of regulation. This output is

guaranteed to provide a logic low level (<0.4V) whenever

the Main Output supply is below a threshold set by the Reset

Adjust pin strap option (see Reset Adjust section) or is pulled

above 5.75V. This general reset prevents erratic system op-

eration which may occur with out-of-specification supply po-

tentials.

The Reset Output has an active pull down which can sink up

to 15mA of current and a passive pull-up (through a 4K

Ω re-

sistor) to the Main Output to ensure voltage compatibility

with the system supply. Capacitive loading on this reset line

will directly affect the rise time of the reset signal. The Reset

Output will maintain a logic low level with a Main Output volt-

age of only 1V. Below 1V the active pull-down device

switches OFF (sink current of only 500µA). At such a low

supply potential, system controllers are generally inopera-

tive.

The Reset Output has a built-in delay time interval which is

programmable by the section of the delay capacitor.

Reset Adjust (pin 11)

The low Vmain threshold voltage for generating a system re-

set can be shifted by 500mV through the use of a pin strap to

ground on pin 11. With this pin shorted to ground the thresh-

old is between 4.5V and 4.7V. With this pin left open the

threshold is shifted to between 4.0V and 4.2V. This lower

threshold allows the system to remain operational longer

during power down. The higher threshold ensures that the

system is reset when the nominal 5V supply is low by 10%,

which in some cases can produce uncertain microprocessor

operation.

Delay Capacitor (pin 8)

Figure 2. Reset Generator and Watchdog Circuitry

DS101296-17

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