ADP1754/ADP1755

Data Sheet

Rev. E | Page 12 of 20

A CH1

920mV

1

2

T

EN

500mV/DIV

ADJUSTABLE OUTPUT VOLTAGE (ADP1755)

The output voltage of the ADP1755 can be set over a 0.75 V to

3.3 V range. The output voltage is set by connecting a resistive

voltage divider from VOUT to ADJ. The output voltage is calcu-

lated using the following equation:

(2)

where:

R1 is the resistor from VOUT to ADJ.

R2 is the resistor from ADJ to GND.

The maximum bias current into ADJ is 150 nA. Therefore, to

achieve less than 0.5% error due to the bias current, use values

less than 60 kΩ for R2.

ENABLE FEATURE

The ADP1754/ADP1755 use the EN pin to enable and disable

the VOUT pins under normal operating conditions. As shown

in Figure 28, 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.

2

A CH1

1.05V

1

T

EN

500mV/DIV

Figure 28. Typical EN Pin Operation

As shown in Figure 28, the EN pin has hysteresis built in. This

hysteresis 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/inactive thresholds are derived from the VIN

voltage. Therefore, these thresholds vary with changing input

voltage. Figure 29 shows typical EN active/inactive thresholds

when the input voltage varies from 1.6 V to 3.6 V.

1.1

0.5

0.6

0.7

0.8

0.9

1.0

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

INPUT VOLTAGE (V)

EN ACTIVE

EN INACTIVE

Figure 29. Typical EN Pin Thresholds vs. Input Voltage

POWER-GOOD FEATURE

The ADP1754/ADP1755 provide a power-good pin, PG, to

indicate the status of the output. This open-drain output

shutdown mode, current-limit mode, thermal shutdown, or

if it falls below 90% of the nominal output voltage, PG imme-

diately transitions low. During soft start, the rising threshold of

the power-good signal is 93.5% of the nominal output voltage.

The open-drain output is held low when the ADP1754/ADP1755

have sufficient input voltage to turn on the internal PG transistor.

An optional soft start delay can be detected. The PG transistor

Power-good accuracy is 93.5% of the nominal regulator output

voltage when this voltage is rising, with a 90% trip point when

this voltage is falling.

Regulator input voltage brownouts or glitches trigger a power

drops below 90%.