Evaluation Board User Guide UG-055
Rev. A | Page 5 of 12
If the load current is large, the user must connect the voltmeter
as close as possible to the output capacitor to reduce the effects
of IR drops.
LINE REGULATION MEASUREMENTS
For line regulation measurements, the output of the regulator
is monitored while its input is varied. For good line regulation,
the output must change as little as possible with varying input
levels. To ensure that the device is not in dropout mode during
this measurement, V
IN
must be varied between V
OUTNOM
+ 0.3 V
(or 2.3 V, whichever is greater) and V
INMAX
.
For example, for the ADP122 with a fixed 3.3 V output, V
IN
must be varied between 3.6 V and 5.5 V. This measurement
can be repeated under different load conditions. Figure 7
shows the typical line regulation performance of the ADP122
with a fixed 3.3 V output.
3.284
3.286
3.288
3.290
3.292
3.294
3.296
V
IN
(V)
V
OUT
(V)
08524-007
3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4
I
OUT
= 100µA
I
OUT
= 1mA
I
OUT
= 10mA
I
OUT
= 100mA
I
OUT
= 200mA
I
OUT
= 300mA
Figure 7. Output Voltage (V
OUT
) vs. Input Voltage (V
IN
) at T
A
= 25°C
LOAD REGULATION MEASUREMENTS
For load regulation measurements, the output of the regulator
is monitored while the load is varied. For good load regulation,
the output must change as little as possible with varying load.
The input voltage must be held constant during this measure-
ment. The load current can be varied from 0 mA to 300 mA.
Figure 8 shows the typical load regulation performance of the
ADP122 with a fixed 3.3 V output for an input voltage of 3.6 V.
3.2895
3.2900
3.2905
3.2910
3.2915
3.2920
3.2925
3.2930
3.2935
3.2940
3.2945
0.1 1 10 100 1000
I
OUT
(mA)
V
OUT
(V)
08524-008
Figure 8. Output Voltage (V
OUT
) vs. Load Current (I
OUT
) at V
IN
= 3.6 V,
V
OUT
= 3.3 V, T
A
= 25°C
DROPOUT VOLTAGE MEASUREMENTS
Dropout voltage can be measured using the configurations
shown in Figure 5 and Figure 6. Dropout voltage is defined as
the input-to-output voltage differential when the input voltage
is set to the nominal output voltage. This applies only to output
voltages above 2.3 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. Figure 9
shows the typical curve of dropout voltage measurements with
different load currents.
0
10
20
30
40
50
60
70
1 10 100 1000
I
OUT
(mA)
DROPOUT (mV)
08524-009
Figure 9. Dropout Voltage vs. Load Current (I
OUT
) at V
OUT
= 3.3 V, T
A
= 25°C
