ADP1761ACPZ1.25-R7 datasheet(13/19 Pages) AD

13 / 19 page

ADP1761

Data Sheet

Rev. 0 | Page 12 of 18

ADJUSTABLE OUTPUT VOLTAGE

The output voltage of the ADP1761 can be set over a 0.5 V to

1.5 V range. Connect a resistor (RADJ) from the VADJ pin to

ground to set the output voltage. To calculate the output voltage,

use the following equation:

VOUT = AD × (RADJ × IADJ)

(3)

where:

AD is the gain factor with a typical value of 3.0 between the

VADJ pin and the VOUT pin.

IADJ is the 50.0 μA constant current out of the VADJ pin.

ENABLE FEATURE

The ADP1761 uses the EN pin to enable and disable the VOUT

pins under normal operating conditions. As shown in Figure 27,

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.

CH1 200mV

CH2 200mV

M4.0ms

A CH1

768mV

8.26ms

VOUT

Figure 27. 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.

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

EN VOLTAGE (V)

0.55 0.56 0.57 0.58 0.59 0.60 0.61 0.62 0.63 0.64 0.65

Figure 28. Output Voltage vs. Typical EN Pin Voltage, VOUT = 1.3 V

POWER-GOOD (PG) FEATURE

The ADP1761 provides a power-good pin (PG) to indicate the

status of the output. This open-drain output requires an external

pull-up resistor that can be connected to VIN or VOUT. If the

device is in shutdown mode, current-limit mode, or thermal

shutdown, or if it falls below 90% of the nominal output voltage,

PG immediately transitions low. During soft start, the rising

threshold of the power-good signal is 95% of the nominal

output voltage.

The open-drain output is held low when the ADP1761 has a

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

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

terminated via a pull-up resistor to VOUT or VIN.

Power-good accuracy is 92.5% of the nominal regulator output

voltage when this voltage is rising, with a 95% trip point when

this voltage is falling.

Regulator input voltage brownouts or glitches trigger a power

no good if VOUT falls below 92.5%.

A normal power-down triggers a power good when VOUT is at 95%.

CH1 1.00V

CH2 1.00V

M100µs

A CH4

420mV

T 228.0000µs

CH4 1.00V

VIN

VOUT

Figure 29. Typical PG Behavior vs. VOUT, VIN Rising (VOUT = 1.3 V)

CH1 1.00V

CH2 1.00V

M200µs

A CH1

3.00V

T 0.000000s

CH4 1.00V

VIN

VOUT

Figure 30. Typical PG Behavior vs. VOUT, VIN Falling (VOUT = 1.3 V)

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