ADP1764ACPZ1.25-R7 datasheet(14/20 Pages) AD

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ADP1764

Data Sheet

Rev. A | Page 14 of 20

ADJUSTABLE OUTPUT VOLTAGE

The output voltage of the ADP1764 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

(VOUT), use the following equation:

VOUT = AD × (RADJ × IADJ)

(3)

where:

AD is the gain factor with a typical value of 2.99 between the

VADJ pin and VOUT pin.

IADJ is the 50 μA constant current out of the VADJ pin.

ENABLE FEATURE

The ADP1764 uses the EN pin to enable and disable the VOUT

pins under normal operating conditions. As shown in Figure 42,

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

10.00ms

100kSPS

10k POINTS

CH1

1.21V

121.9200ms

VOUT

Figure 42. Typical EN Pin Operation

As shown in Figure 43, the EN pin has built in hysteresis. 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

0.59

0.66

EN THRESHOLD (V)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

0.60

0.61

0.62

0.63

0.64

0.65

TA = +125°C

TA = +85°C

TA = +25°C

TA = 0°C

TA = –40°C

Figure 43. Output Voltage vs. EN Threshold, VOUT = 1.3 V

POWER-GOOD (PG) FEATURE

The ADP1764 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 96.5% of the nominal

output voltage.

The open-drain output is held low when the ADP1764 has

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 VIN or VOUT.

Power-good accuracy is 93.8% of the nominal regulator output

voltage when this voltage is rising, with a 96.5% trip point when

this voltage is falling.

Regulator input voltage brownouts or glitches trigger a power

no good if VOUT falls below 93.8%.

A normal power-down triggers a power good when VOUT is

at 96.5%.

CH1 1V

CH2 1V

CH3 1V

200µs

5.00MSPS

10k POINTS

CH2

1.30V

–70.00000µs

VOUT

Figure 44. VOUT vs. Typical PG Voltage Behavior, VIN Rising (VOUT = 1.3 V)

CH1 1V BW

CH2 1V BW

CH3 1V BW

200µs

500MSPS

1M POINTS

CH2

700mV

–5.20000µs

VOUT

Figure 45. VOUT vs. Typical PG Voltage Behavior, VIN Falling (VOUT = 1.3 V)

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