ADP7104CPZ-REDYKIT(RevB) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADP7104CPZ-REDYKIT Datasheet PDF : 28 Pages
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ADP7104
PROGRAMABLE UNDERVOLTAGE LOCKOUT (UVLO)
The ADP7104 uses the EN/UVLO pin to enable and disable
the VOUT pin under normal operating conditions. As shown
in Figure 64, when a rising voltage on EN crosses the upper
threshold, VOUT turns on. When a falling voltage on EN/
UVLO crosses the lower threshold, VOUT turns off. The
hysteresis of the EN/UVLO threshold is determined by
the Thevenin equivalent resistance in series with the EN/
UVLO pin.
2.0
1.8
1.6
1.4
1.2
1.0
VOUT, EN RISE
VOUT, EN FALL
0.8
0.6
0.4
0.2
0
1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00
Figure 64. Typical VOUT Response to EN Pin Operation
The upper and lower thresholds are user programmable and can
be set using two resistors. When the EN/UVLO pin voltage is
below 1.22 V, the LDO is disabled. When the EN/UVLO pin
voltage transitions above 1.22 V, the LDO is enabled and 10 µA
hysteresis current is sourced out the pin raising the voltage, thus
providing threshold hysteresis. Typically, two external resistors
program the minimum operational voltage for the LDO. The
resistance values, R1 and R2 can be determined from:
R1 = VHYS/10 μA
R2 = 1.22 V × R1/(VIN − 1.22 V)
where:
VIN is the desired turn-on voltage.
VHYS is the desired EN/UVLO hysteresis level.
Data Sheet
Hysteresis can also be achieved by connecting a resistor in
series with EN/UVLO pin. For the example shown in Figure 65,
the enable threshold is 2.44 V with a hysteresis of 1 V.
VIN = 8V
CIN +
1µF
ON
OFF
100kΩ
100kΩ
VIN VOUT
SENSE
EN/
UVLO
PG
GND
+ COUT
1µF
VOUT = 5V
100kΩ
PG
Figure 65. Typical EN Pin Voltage Divider
Figure 64 shows the typical hysteresis of the EN/UVLO pin.
This prevents on/off oscillations that can occur due to noise
on the EN pin as it passes through the threshold points.
The ADP7104 uses an internal soft-start to limit the inrush
current when the output is enabled. The start-up time for the
3.3 V option is approximately 580 μs from the time the EN
active threshold is crossed to when the output reaches 90%
of its final value. As shown in Figure 66, the start-up time is
dependent on the output voltage setting.
6
5V
5
4
3.3V
3
2
ENABLE
1
0
0
500
1000
1500
2000
TIME (µs)
Figure 66. Typical Start-Up Behavior
Rev. B | Page 18 of 28
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