L4995RKTR datasheet(18/35 Pages) STMICROELECTRONICS

18 / 35 page

Application information

L4995

18/35

Doc ID 13103 Rev 14

3.1

Voltage regulator

Voltage regulator uses a p-channel transistor as a regulating element. With this structure,

very low dropout voltage at current up to 500mA is obtained. The output voltage is regulated

up to transient input supply voltage of 40V. No functional interruption due to over-voltage

pulses is generated. A short circuit protection to GND is provided.

The voltage regulator is active when En is high.

Figure 28.

Behavior of output current versus regulated voltage Vo

3.2

Reset

The reset circuit supervises the output voltage Vo. The Vo_th reset threshold is defined with

the in-ternal reference voltage and a resistor output divider. If the output voltage becomes

lower than Vo_th then Res goes low with a reaction time trr. The reset low signal is

guaranteed for an output voltage Vo greater than 1V.

When the output voltage becomes higher than Vo_th then Res goes high with a delay trd.

This delay is obtained by an internal oscillator.

The oscillator period is given by:

Equation 1

Tosc = [(VRhth-VRlth) x Ctr] / Icr + [(VRhth-VRlth) x Ctr] / Idr

where:

Icr:is an internally generated charge current

Idr:is an internally generated discharge current

VRhth, VRlth:are two voltages defined with the output voltage and a resistor output

divider

Ctr:is an external capacitance.

trd is given by:

Equation 2

trd = (VRhth x Ctr)/Icr + 3 x Tosc

Vo_ref

Iout

Ishort Ilim

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