Modifying The Evaluation Board - Analog Devices EVAL-ADP2311 User Manual

UG-653
Measuring Output Voltage Ripple
To observe the output voltage ripple, place the oscilloscope probe
across the output capacitor with the probe ground lead connected
to the negative (−) capacitor terminal and the probe tip placed at
the positive (+) capacitor terminal. Set the oscilloscope to ac,
10 mV/division, 2 µs/division time base, and 20 MHz bandwidth.
A standard oscilloscope probe has a long wire ground clip. For
high frequency measurements, this ground clip picks up high
frequency noise and injects it into the measured output ripple.
Figure 2 shows an easy way to measure the output ripple properly.
It requires removing the oscilloscope probe sheath and wrapping
an unshielded wire around the oscilloscope probe. By keeping
the ground length of the oscilloscope probe as short as possible,
the true ripple can be measured.
Figure 2. Measuring Output Voltage Ripple

MODIFYING THE EVALUATION BOARD

To modify the ADP2311evaluation board configuration, unsolder
and/or replace/remove the appropriate passive components or
jumpers on the board.
Changing the Output Voltages
The output voltage setpoints of the
replacing the R1, R2, R5, and R8 resistors with the resistor values
shown in Table 1.
Table 1. Resistive Divider for Various Output Voltages
V (V) R1/R5, ±1% (kΩ)
OUT
1.0 10
1.2 10
1.5 15
1.8 20
2.5 47.5
3.3 10
5.0 22
ADP2311 can be changed by
R2/R8, ±1% (kΩ)
15
10
10
10
15
2.21
3
Rev. 0 | Page 4 of 8
EVAL-ADP2311 User Guide
To limit the output voltage accuracy degradation due to the FBx
bias current (0.1 µA maximum) to less than 0.5% (maximum),
ensure that the bottom divider string resistors, R2 and R8, is less
than 30 kΩ.
The top resistors, R1 and R5, value is calculated using the following
equations:
For Channel 1,

−
V 0.6 V

OUT1
R1 = R2 ×

0.6 V

For Channel 2,

−
V 0.6 V

OUT2
R5 = R8 ×

0.6 V

When the output voltage of Channel 1 is changed, the values of
the inductor (L1) and the output capacitors (C4 and C5) must
be recalculated and changed to ensure stable operation (see the
ADP2311 data sheet for details on external component selection).
Likewise, if the output voltage of Channel 2 is changed, the values
of the inductor (L2) and the output capacitors (C8 and C9)
must be recalculated and changed.
Changing the VIN Threshold of Power Fail (PFI)
The evaluation board sets the V
V at 8.61 V. It can be changed with different R4 and
PFI_FALLING
R7 value.
Using the following equation to calculate the R4 and R7:
R 4
= ×
V 0 6 . V
PFI _ RISING
= ×
V . 0 575 V
PFI _ FALLING
Changing the VIN Threshold of Voltage Monitoring (VM2)
The evaluation board sets the V
V at 5 V. It can be changed with different R3 and R6 value.
VM2_FALLNG
Using the following equation to calculate R3 and R6:
R
= ×
V . 0 65 V
VM 2 _ RISING
R
= ×
V 0 6 . V
VM 2 _ FALLING








at 8.99 V and the
PFI_RISING
+
R 7
R 7
+
R 4 R 7
R 7
at 5.41 V and the
VM2_RISING
+
3 R 6
R 6
+
3 R 6
R 6