ADP1715 Analog Devices, ADP1715 Datasheet - Page 11

• Manufacturer Part Number: ADP1715
• Description: 500 mA Low-Dropout CMOS Linear Regulator with Soft Start
• Manufacturer: Analog Devices

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
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.
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.
V
4
3
2
1
0
OUT
0
Figure 29. ADP1716 Output Voltage vs. Tracking Voltage
= 0.8 V (1 + R1/R2)
with Nominal Output Voltage Set to 3 V
1
2
V
TRK
(V)
3
4
5
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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.
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
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
Figure 30. ADP1715 Adjustable Typical EN Pin Operation
2.50
Figure 31. Typical EN Pin Thresholds vs. Input Voltage
2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25
EN
OUT
EN ACTIVE
EN INACTIVE
TIME (1ms/DIV)
V
IN
ADP1715/ADP1716
(V)
V
V
C
I
LOAD
IN
OUT
OUT
= 5V
= 1.6V
= 2.2µF
= 10mA
HYSTERESIS
5.50