ADP130AUJZ-2.5-R7 datasheet(14/20 Pages) AD

14 / 20 page

ADP130

Rev. 0 | Page 14 of 20

Use Equation 1 to determine the worst-case capacitance,

accounting for capacitor variation over temperature, compo-

nent tolerance, and voltage.

CEFF = COUT × (1 − TEMPCO) × (1 − TOL)

(1)

where:

CEFF is the effective capacitance at the operating voltage.

TEMPCO is the worst-case capacitor temperature coefficient.

TOL is the worst-case component tolerance.

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

COUT = 0.94 μF at 1.8 V, as shown in Figure 36.

Substituting these values in Equation 1 yields the following:

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 tempera-

ture and tolerance at the chosen output voltage.

To guarantee the performance of the ADP130, it is imperative

that the effects of dc bias, temperature, and tolerances on the

behavior of the capacitors be evaluated for each application.

UNDERVOLTAGE LOCKOUT

The ADP130 has an internal undervoltage lockout circuit that

disables all inputs and the output when the input voltage is less

than approximately 2.1 V. This ensures that the ADP130 inputs

and the output behave in a predictable manner during power-up.

ENABLE FEATURE

The ADP130 uses the EN pin to enable and disable the VOUT

pin under normal operating conditions. As shown in Figure 37,

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.

CH1 500mV

CH2 500mV

M10ms

A CH2

640mV

T 30%

–VOUT = 1.8V

CIN = COUT = 1µF

VOUT

500mV/DIV

Figure 37. Typical EN Pin Operation

As shown in Figure 37, the EN pin has built-in hysteresis. This

prevents on/off oscillations that can occur due to noise on the

EN pin as it passes through the threshold points.

The EN pin active and inactive thresholds are derived from the

VIN voltage. Therefore, these thresholds vary with changing input

voltage. Figure 38 shows typical EN active and inactive thresholds

when the VBIAS voltage varies from 2.3 V to 5.5 V.

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

2.3

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

VBIAS (V)

EN ACTIVE

EN INACTIVE

Figure 38. Typical EN Pin Thresholds vs. Input

The ADP130 uses an internal soft start to limit the inrush current

when the output is enabled. The start-up time for the 0.8 V option

is approximately 180 μs from the time at which the EN active

threshold is crossed to when the output reaches 90% of its final

value. The start-up time depends somewhat on the output voltage

setting and increases slightly as the output voltage increases.

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

100

200

300

400

500

600

700

800

900 1000

TIME (µs)

VBIAS = 2.3V

VIN = 3.6V

ILOAD = 10mA

ENABLE

3.0V

1.8V

1.2V

0.8V

Figure 39. Typical Start-Up Time

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