Obsolete

Product(s)

- Obsolete

Product(s)

L4989

Application information

11/19

3

Application information

3.1

Voltage regulator

The voltage regulator uses a p-channel MOS transistor as a regulating element. With this

structure a very low dropout voltage at current up to 150mA 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.The voltage Regulator is always active and not depending

on the state of WEn input pin. A short circuit protection to GND is provided.

Figure 3.

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:

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:

trd = 512 x Tosc

The Reset is always active and not depending on the state of WEn input pin.

Vo

Vo_ref

Iout

Ishort Ilim