ADM7155ARDZ-02-R7 datasheet(17/24 Pages) AD

17 / 24 page

Data Sheet

ADM7155

Rev. C | Page 17 of 24

PROGRAMMABLE PRECISION ENABLE

The ADM7155 uses the EN pin to enable and disable the VOUT

pin under normal operating conditions. As shown in Figure 50,

when a rising voltage on EN crosses the upper threshold,

nominally 1.22 V, VOUT turns on. When a falling voltage on EN

crosses the lower threshold, nominally 1.13 V, VOUT turns off.

The hysteresis of the EN threshold is approximately 90 mV.

EN PIN VOLTAGE (V)

1.3

1.2

1.1

1.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

–40°C

–5°C

+25°C

+85°C

+125°C

Figure 50. Typical VOUT Response to EN Pin Operation

TIME (ms)

4.0

3.6

3.2

2.8

2.4

2.0

1.6

1.2

0.8

0.4

3.5

3.0

2.5

2.0

1.5

1.0

0.5

ENABLE (VEN)

VOUT

Figure 51. Typical VOUT Response to EN Pin Operation (VEN),

VOUT = 3.3 V, VIN = 5 V, CBYP = 1 μF

INPUT VOLTAGE (V)

5.5

5.0

4.5

4.0

3.5

3.0

2.5

1.100

1.250

1.225

1.200

1.175

1.150

1.125

–40°C RISING

+25°C RISING

+125°C RISING

–40°C FALLING

+25°C FALLING

+125°C FALLING

Figure 52. Typical EN Threshold vs. Input Voltages (VIN) for Different

Temperatures

The upper and lower thresholds are user programmable and can

be set higher than the nominal 1.22 V threshold by using two

resistors. The resistance values, REN1 and REN2, can be

determined from

REN1 = REN2 × (VIN − 1.22 V)/1.22 V

where:

REN2 typically ranges from 10 kΩ to 100 kΩ.

VIN is the desired turn-on voltage.

The hysteresis voltage increases by the factor

(REN1 + REN2)/REN2

For the example shown in Figure 53, the EN threshold is 2.44 V

with a hysteresis of 200 mV.

VOUT

REF_SENSE

REF

REF = 1.2V

VIN

ADM7155

GND

CREF

1µF

CIN

10µF

COUT

10µF

OFF

VIN = 3.5V

VOUT = 3.0V

BYP

CBYP

1µF

VREG

CREG

10µF

VOUT = 1.2V × (R1 + R2)/R2

1kΩ < R2 < 200kΩ

VBYP

VREG

REN1

100kΩ

REN2

100kΩ

Figure 53. Typical EN Pin Voltage Divider

Figure 53 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.

START-UP TIME

The ADM7155 uses an internal soft start to limit the inrush

current when the output is enabled. The start-up time for a 3.3 V

output is approximately 1.2 ms from the time the EN active

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

final value.

The rise time in seconds of the output voltage (10% to 90%) is

approximately

0.0012 × CBYP

where CBYP is in microfarads.

ADM7155ARDZ-02-R7 数据表(PDF) 17 Page - Analog Devices

ADM7155ARDZ-02-R7 数据表(HTML) 17 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

数据表下载

链接网址

ADM7155ARDZ-02-R7 数据表(PDF) 17 Page - Analog Devices

ADM7155ARDZ-02-R7 数据表(HTML) 17 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

数据表 下载

链接网址

数据表下载