ADP123 Analog Devices, ADP123 Datasheet - Page 13

• Manufacturer Part Number: ADP123
• Description: 5.5 V Input, 300 mA, Low Quiescent Current, CMOS Linear Regulator, Adjustable Output Voltage
• Manufacturer: Analog Devices

Therefore, the capacitor chosen in this example meets the
minimum capacitance requirement of the LDO over tem-
perature and tolerance at the chosen output voltage.
To guarantee the performance of the ADP122/ADP123, it is
imperative that the effects of dc bias, temperature, and tolerances
on the behavior of the capacitors are evaluated for each application.
UNDERVOLTAGE LOCKOUT
The ADP122/ADP123 have an internal undervoltage lockout
circuit that disables all inputs and the output when the input
voltage is less than approximately 2 V. This ensures that the
ADP122/ADP123 inputs and the output behave in a predictable
manner during power-up.
ENABLE FEATURE
The ADP122/ADP123 uses the EN pin to enable and disable the
VOUT pin under normal operating conditions. As shown in
Figure 35, when a rising voltage on EN crosses the active threshold,
VOUT turns on. Conversely, when a falling voltage on EN crosses
the inactive threshold, VOUT turns off.
As shown in Figure 35, the EN pin has built-in hysteresis. This
prevents on/off oscillations that may occur due to noise on the
EN pin as it passes through the threshold points.
The active and inactive thresholds of the EN pin are derived from
the VIN voltage. Therefore, these thresholds vary as the input
voltage changes. Figure 36 shows typical EN active and inactive
thresholds when the VIN voltage varies from 2.3 V to 5.5 V.
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
0.2
Figure 35. Typical EN Pin Operation
0.4
0.6
V
0.8
EN
1.0
1.2
1.4
1.6
Rev. A | Page 13 of 24
The ADP122/ADP123 utilize an internal soft start to limit the
in-rush current when the output is enabled. The start-up time
for the 2.8 V option is approximately 350 µs from the time the
EN active threshold is crossed to when the output reaches 90%
of its final value. As shown in Figure 37, the start-up time is
dependent on the output voltage setting and increases slightly
as the output voltage increases.
1.0
1.1
0.9
0.8
0.7
0.6
0.5
1
2
2.2
CH1
Figure 36. Typical EN Pin Thresholds vs. Input Voltage
1.00V
2.7
CH2 1.00V
Figure 37. Typical Start-Up Time
3.2
FALLING
RISING
3.7
V
IN
M200µs
T
(V)
V
V
V
V
IN
OUT
OUT
OUT
4.2
600.000µs
= 5V
ADP122/ADP123
= 4.2V
= 3.3V
= 2.8V
4.7
A CH1
5.2
3.08V