ADP7182ACPZ-R7 datasheet(23/31 Pages) AD

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Data Sheet

ADP7182

Rev. I | Page 23 of 31

ENABLE PIN OPERATION

The ADP7182 uses the EN pin to enable and disable the VOUT

pin under normal operating conditions. When EN is at ±2 V with

respect to GND, VOUT turns on, and when EN is at 0 V, VOUT

turns off. For automatic startup, EN can be connected to VIN.

When the device is disabled, a ~220 kΩ resistor connects to the

VOUT pin, which pulls the VOUT pin up to GND.

The ADP7182 provides a dual polarity enable pin (EN) that turns

on the LDO when |VEN| ≥ 2 V. The enable voltage can be positive or

negative with respect to ground.

–2.0

–1.5

–1.0

–0.5

–2.0

–1.5

–1.0

–0.5

0.5

1.0

1.5

ENABLE VOLTAGE (V)

VOUT WITH RISING VEN

VOUT WITH FALLING VEN

Figure 82. Typical EN Pin Operation

Figure 82 shows the typical hysteresis of the EN pin. This prevents

on/off oscillations that can occur due to noise on the EN pin as

it passes through the threshold points.

Figure 83 shows typical EN thresholds when the input voltage

varies from −2.7 V to −28 V.

1.0

–2.0

–1.5

–1.0

–0.5

0.5

–30

–26

–22

–18

–14

–10

–6

–2

INPUT VOLTAGE (V)

ENABLE+

DISABLE+

ENABLE–

DISABLE–

Figure 83. Typical EN Pin Thresholds vs. Input Voltage

Figure 84 and Figure 85 show the start-up behavior for a −5 V

output with positive and negative going enable signals.

CH1 500mV BW CH2 500mV BW M40µs

A CH1

590mV

T 10.20%

VOUT

Figure 84. Typical Start-Up Behavior, Positive Going Enable

CH1 500mV BW CH2 500mV BW M40µs A CH1

–580mV

T 10.20%

VOUT

Figure 85. Typical Start-Up Behavior, Negative Going Enable

SOFT START

The ADP7182 uses an internal soft start to limit the inrush current

when the output is enabled. The start-up time for the −5 V option

is approximately 450 μs from the time the EN active threshold is

crossed to when the output reaches 90% of the final value. As

shown in Figure 86, the start-up time is dependent on the output

voltage setting.

–6

–5

–4

–3

–2

–1

1000

900

800

700

600

500

400

300

200

100

TIME (µs)

VEN

VOUT = –1.22V

VOUT = –3V

VOUT = –5V

Figure 86. Typical Start-Up Behavior, Different Output Voltages

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