ADM7151ACPZ-04-R2 datasheet(18/24 Pages) AD

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ADM7151

Data Sheet

Rev. B | Page 18 of 24

ENABLE (EN) AND UNDERVOLTAGE LOCKOUT

(UVLO)

The ADM7151 uses the EN pin to enable and disable the VOUT

pin under normal operating conditions. As shown in Figure 55,

when a rising voltage on EN crosses the upper threshold,

VOUT turns on. When a falling voltage on EN crosses the lower

threshold, VOUT turns off. The hysteresis varies as a function

of the input voltage. For example, the EN hysteresis is

approximately 200 mV with an input voltage of 4.5 V.

VEN (V)

1.6

1.5

1.0

1.2

1.4

1.1

1.3

3.5

3.0

2.5

2.0

1.5

1.0

0.5

VOUT_EN_RISE

VOUT_EN_FALL

Figure 55. Typical VOUT Response to EN Pin Operation, VOUT = 3.3 V, VIN = 5 V

VIN (V)

+125°C

+25°C

–40°C

1.4

3.2

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

Figure 56. Typical EN Rise Threshold vs. Input Voltage (VIN) for Various

Temperatures

VIN (V)

+125°C

+25°C

–40°C

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

Figure 57. Typical EN Fall Threshold vs. Input Voltage (VIN) for Various

Temperatures

The ADM7151 also incorporates an internal undervoltage

lockout circuit to disable the output voltage when the input

voltage is less than the minimum input voltage rating of the

regulator. The upper and lower thresholds are internally fixed

with approximately 300 mV of hysteresis.

VIN (V)

4.5

4.4

4.0

4.2

4.3

4.1

3.5

3.0

2.5

2.0

1.5

1.0

0.5

VOUT_VIN_RISE

VOUT_VIN_FALL

Figure 58. Typical UVLO Hysteresis, VOUT = 3.3 V

Figure 58 shows the typical hysteresis of the UVLO function.

This hysteresis prevents on/off oscillations that can occur due to

noise on the input voltage as it passes through the threshold

points.

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