OUT2 pin the output voltage 2 can be pro-

grammed to the value of







1

+







5.05V.

For an exact calculation the temperature coeffi-

cient (Tc -2000pprm) of the internal resistor

mode should not have a capacitive burden be-

cause this would reduce the phase margin of the

regulator loop.

Reset circuit

The reset circuit supervises the standby output

voltage. The reset output (RES) is defined from

≥ 1V.

The reset threshold of 4.7V is defined with the in-

ternal reference voltage (note 9) and standby out-

put divider, when pin PR is left open. The reset

threshold voltage can be programmed in the

range from 3.8V to 4.7V by connecting an exter-

nal resistor from pin PR to GND.

be calculated with:

=

22K

4.7K

−1

=

⋅ 0.6V

1

µA

(note 5)

=

1

µA

(note 6)

The reaction time of the reset circuit originates

from the noise immunity. Standby output voltage

drops below the reset threshold only a bit longer

than the reaction time results in a shorter reset

delay time. The nominal reset delay time will be

generated for standby output voltage drops longer

than approximately 50

µs.

The minimum rset time is generated if reset con-

dition only occures for a short time triggering a re-

reset can be related to output2 on request. If

higher charge currents for the reset capacitor are

used to increase the current. We recommended

the use of 10K

Ω to 5V as an output pull up.

Sense Comparator

The sense comparator compares an input signal

with an internal voltage reference of typical 1.23V.

The use of an external voltage divider makes this

comparator very flexible in the application. It can

be used to supervise the input voltage either be-

fore or after the protection diode and to give addi-

tional information to the microprocessor like low

voltage warnings. We recommended the use of

10K

Ω to 5V as an output pull up.

Note 9:

is present, the reference is operating.

Thermal Protection

Both outputs are provided with an overtempera-

ture shut down regulation power dissipation down

to uncritical values.

Output 2 will shut down approximately 10K before

output 1.

Under normal conditions shut down of output 2

will allow the chip to cool down again. Thus out-

put 1 will be unaffected.

The thermal shut down reduces the output volt-

ages until power dissipation and the flow of ther-

mal energy out of the chip balance.

Transient Sensitivity

put transients.

Precise Data will be issued as soon as samples

are available.

L4938E - L4938ED - L4938EPD

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