ADP170(RevC) 데이터 시트보기 (PDF) - Analog Devices
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ADP170 Datasheet PDF : 20 Pages
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Data Sheet
In this example, the worst-case temperature coefficient
(TEMPCO) over −40°C to +85°C is assumed to be 15% for an
X5R dielectric. The tolerance of the capacitor (TOL) is assumed
to be 10%, and CBIAS is 0.94 μF at 1.8 V, as shown in Figure 29.
Substituting these values in Equation 1 yields
CEFF = 0.94 μF × (1 − 0.15) × (1 − 0.1) = 0.719 μF
Therefore, the capacitor chosen in this example meets the
minimum capacitance requirement of the LDO over temper-
ature and tolerance at the chosen output voltage.
To guarantee the performance of the ADP170/ADP171, it is
imperative that the effects of dc bias, temperature, and toler-
ances on the behavior of the capacitors are evaluated for each
application.
UNDERVOLTAGE LOCKOUT
The ADP170/ADP171 have an internal undervoltage lockout
circuit that disables all inputs and the output when the input
voltage is less than approximately 1.2 V. This ensures that the
ADP170/ADP171 inputs and the output behave in a predictable
manner during power-up.
ENABLE FEATURE
The ADP170/ADP171 use the EN pin to enable and disable the
VOUT pin under normal operating conditions. As shown in
Figure 30, when a rising voltage on EN crosses the active
threshold, VOUT turns on. When a falling voltage on EN
crosses the inactive threshold, VOUT turns off.
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
VEN
Figure 30. ADP170/ADP171 Typical EN Pin Operation
As shown in Figure 30, the EN pin has hysteresis built in. This
prevents on/off oscillations that can occur due to noise on the
EN pin as it passes through the threshold points.
ADP170/ADP171
The EN pin active/inactive thresholds are derived from the VIN
voltage. Therefore, these thresholds vary with changing input
voltage. Figure 31 shows typical EN active/inactive thresholds
when the input voltage varies from 1.6 V to 3.6 V.
1.2
1.1
1.0
EN ACTIVE
0.9
0.8
0.7
EN INACTIVE
0.6
0.5
0.4
VIN (V)
Figure 31. Typical EN Pin Thresholds vs. Input Voltage
The ADP170/ADP171 utilize an internal soft start to limit the
inrush current when the output is enabled. The start-up time
for the 1.8 V option is approximately 120 μs from the time the
EN active threshold is crossed to when the output reaches 90%
of its final value. As shown in Figure 32, the start-up time is
dependent on the output voltage setting.
EN
VOUT = 3.0V
VOUT = 1.8V
VOUT = 0.8V
1
2
CH1 1.00V
CH2 1.00V BW M20.0µs A CH1
T 79.8000µs
Figure 32. Typical Start-Up Time
2.72V
Rev. C | Page 13 of 20
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