ADP1715/ADP1716

Rev. 0 | Page 11 of 20

ADJUSTABLE OUTPUT VOLTAGE

(ADP1715 ADJUSTABLE)

The ADP1715 adjustable version can have its output voltage

set over a 0.8 V to 5.0 V range. The output voltage is set by

connecting a resistive voltage divider from OUT to ADJ. The

output voltage is calculated using the equation

(2)

where:

R1 is the resistor from OUT to ADJ.

R2 is the resistor from ADJ to GND.

The maximum bias current into ADJ is 100 nA, so for less

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

60 kΩ for R2.

TRACK MODE (ADP1716)

The ADP1716 includes a tracking mode feature. As shown in

Figure 29, if the voltage applied at the TRK pin is less than the

nominal output voltage, OUT is equal to the voltage at TRK.

Otherwise, OUT regulates to its nominal output value.

4

05

0

3

2

1

12

34

Figure 29. ADP1716 Output Voltage vs. Tracking Voltage

with Nominal Output Voltage Set to 3 V

For example, consider an ADP1716 with a nominal output

voltage of 3 V. If the voltage applied to its TRK pin is greater

than 3 V, OUT maintains a nominal output voltage of 3 V. If

the voltage applied to TRK is reduced below 3 V, OUT tracks

this voltage. OUT can track the TRK pin voltage from the

nominal value all the way down to 0 V. A voltage divider is

present from TRK to the error amplifier input with a divider

ratio equal to the divider from OUT to the error amplifier.

This sets the output voltage equal to the tracking voltage. Both

divider ratios are set by post-package trim, depending on the

desired output voltage.

ENABLE FEATURE

The ADP1715/ADP1716 use the EN pin to enable and disable

the OUT pin under normal operating conditions. As shown in

Figure 30, when a rising voltage on EN crosses the active

threshold, OUT turns on. When a falling voltage on EN crosses

the inactive threshold, OUT turns off.

1

EN

OUT

TIME (1ms/DIV)

Figure 30. ADP1715 Adjustable Typical EN Pin Operation

As can be seen, the EN pin has hysteresis built in. 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/inactive thresholds are derived from the IN

voltage. Therefore, these thresholds vary with changing input

voltage. Figure 31 shows typical EN active/inactive thresholds

when the input voltage varies from 2.5 V to 5.5 V.

1.4

0.5

2.50

5.50

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25

EN INACTIVE

EN ACTIVE

HYSTERESIS

Figure 31. Typical EN Pin Thresholds vs. Input Voltage