l4993 STMicroelectronics, l4993 Datasheet - Page 10

• Manufacturer Part Number: l4993
• Description: Low Drop Voltage Regulator
• Manufacturer: STMicroelectronics

Application information
3
3.1
3.2
10/23
Application information
The input capacitor Cs > 200nF is necessary for the smoothing of line disturbances. The
output capacitor C01 > 100nF is necessary for the stabilityy of the regulation loop. In order
to damp output voltage oscillations during high load current surges, it is recommended put
an additional electrolytic capacitor C02 > 10µF at the output pin.
Voltage regulator
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 high precision of the output voltage is obtained with a
pre-trimmed reference voltage. A short circuit protection to GND is provided.
Figure 3.
Reset
The reset circuit monitors the output voltage Vo. If the output voltage becomes lower than
Vo_th then Res goes low with a delay time trr. If the output voltage becomes lower than 2.0
V (typ) than Res goes immediately low. 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 512 periods of oscillator. The oscillator period is given by :
and reset pulse delay trd is given by:
where:
Icr = 17.6
Idr = 17.6
µ
µ
A is an internally generated charge current,
A is an internally generated discharge current,
Behavior of output current versus regulated voltage Vo
Tosc = [(Vrhth-Vrlth) x Ctr] / Icr + [(Vrhth-Vrlth) x Ctr] / Idr
Vo_ref
Vo
trd = 512 x Tosc
Ishort Ilim
Iout
L4993