L4989 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L4989' PDF : 19 Pages View PDF
L4989
3
Application information
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
Vo
Vo_ref
duct(s) Ishort Ilim Iout
te Pro 3.2
Reset
ole The reset circuit supervises the output voltage Vo. The Vo_th reset threshold is defined with
s the in-ternal reference voltage and a resistor output divider. If the output voltage becomes
b lower than Vo_th then Res goes low with a reaction time trr. The reset low signal is
O 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.
t(s This delay is obtained by an internal oscillator.
c The oscillator period is given by:
rodu Tosc = [(Vrhth-Vrlth) x Ctr] / Icr + [(Vrhth-Vrlth) x Ctr] / Idr
P where:
teIcr:
le Idr:
Obso Vrhth, Vrlth:
is an internally generated charge current
is an internally generated discharge current
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.
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