Analog Devices ADP5034-1 Evaluation Board ADP5034-1-EVALZ ADP5034-1-EVALZ データシート
製品コード
ADP5034-1-EVALZ
Evaluation Board User Guide
UG-271
Rev. A | Page 7 of 16
Measuring Dropout Voltage of LDO
Dropout voltage is defined as the input-to-output voltage
differential when the input voltage is set to the nominal output
voltage. One way to measure dropout voltage is to get the
output voltage (V
differential when the input voltage is set to the nominal output
voltage. One way to measure dropout voltage is to get the
output voltage (V
OUT
nominal) with V
IN
initially set to V
OUT
nominal + 0.5 V; output load can be set to 100 µA. Then, force
the input voltage equal to V
the input voltage equal to V
OUT
nominal, and measure the output
voltage accordingly (V
OUT
dropout). Dropout voltage is then
calculated as V
OUT
nominal − V
OUT
dropout. This applies only
for output voltages greater than 1.7 V. Dropout voltage increases
with larger loads. For more accurate measurements, a second
voltmeter can be used to monitor the input voltage across the
input capacitor. The input supply voltage may need to be adjusted
to account for IR drops, especially if large load currents
are used.
with larger loads. For more accurate measurements, a second
voltmeter can be used to monitor the input voltage across the
input capacitor. The input supply voltage may need to be adjusted
to account for IR drops, especially if large load currents
are used.
Measuring Ground Current Consumption of LDO
Ground current measurements can determine how much current
the internal circuits of the regulator consume while the circuits
the internal circuits of the regulator consume while the circuits
perform the regulation function. To be efficient, the regulator
needs to consume as little current as possible. Typically, the
regulator uses the maximum current when supplying its largest
load level (300 mA). When the device is disabled, the ground
current drops to less than 1 µA. Refer to Figure 14 for a detailed
instruction on how to perform ground current measurements.
needs to consume as little current as possible. Typically, the
regulator uses the maximum current when supplying its largest
load level (300 mA). When the device is disabled, the ground
current drops to less than 1 µA. Refer to Figure 14 for a detailed
instruction on how to perform ground current measurements.
Cascading an LDO from the Buck Regulator
For certain applications such as analog circuit supplies, the
LDOs are preferred over the bucks because of better noise
performance. Where not all the buck outputs are being used,
the input supply of the LDO can be taken from these outputs.
An example demo board connection is shown in Figure 13
wherein VOUT1 is tied to VIN3, which is the supply of LDO1.
In this configuration, the output voltage of the buck regulator
should have enough headroom with the desired output voltage
of the LDO to guarantee the LDO to operate within
specifications.
LDOs are preferred over the bucks because of better noise
performance. Where not all the buck outputs are being used,
the input supply of the LDO can be taken from these outputs.
An example demo board connection is shown in Figure 13
wherein VOUT1 is tied to VIN3, which is the supply of LDO1.
In this configuration, the output voltage of the buck regulator
should have enough headroom with the desired output voltage
of the LDO to guarantee the LDO to operate within
specifications.
VOLTAGE SOURCE
–
+
VOLTMETER
–
+
1.99711
09808-
1
13
Figure 13. Cascading LDO from Buck