Evaluation Board User Guide
UG-456
Rev. 0 | Page 5 of 12
MODIFYING THE EVALUATION BOARD
The
ADP2442-EVALZ
evaluation board is provided fully
assembled and tested for proper operation. The evaluation
board
has a fixed 5 V output voltage.
CHANGING THE OUTPUT VOLTAGE
The
ADP2442-EVALZ
output regulation voltage is set by a
resistive voltage divider consisting of the R2 and R3 resistors. R2
corresponds to the R
TOP
resistor in the
ADP2442
data sheet, and
R3 corresponds to the R
BOTTOM
resistor in the
ADP2442
data sheet.
The output regulation voltage is determined by
+
×
=
3
V
6
.
0
R
R3
R2
V
OUT
where:
R2
is the value of the top resistor of the voltage divider (R
TOP
).
R3
is the value of the bottom resistor of the voltage divider
(R
BOTTOM
).
V
OUT
is the output regulation voltage in volts.
To set the output regulation voltage to the desired value, first
determine the value of the bottom resistor, R3, by
STRING
FB
I
V
R3
=
where:
V
FB
= 0.6 V, the internal reference.
I
STRING
is the resistor divider string current (greater than 20 µA
nominally).
Once R3 is determined, calculate the value of the top resistor,
R2, by
−
=
FB
FB
OUT
V
V
V
R3
R2
For example, to set the output regulation voltage of the
ADP2442-EVALZ
to 3.3 V, calculate the R2 and R3 values
as shown in the following equations:
kΩ
10
μA
60
V
0.6
=
=
=
STRING
I
FB
V
R3
Ω
Ω
k
45.3
0.6V
V
0.6
V
3.3
k
10
=
−
×
=
−
×
=
FB
FB
OUT
V
V
V
R3
R2
When the output voltage of the
ADP2442-EVALZ
is changed, the
output capacitors (C7 and C8), inductor (L1), and compensation
components (R5 and C10) must be recalculated and changed to
ensure stable operation according to the Applications Information
section in the
ADP2442
data sheet.
Table 2. Programming Output Voltage
Voltage (V)
R2 (kΩ)
R3 (kΩ)
12
190
10
5
73
10
3.3
45
10
1.2
10
10
CHANGING THE SWITCHING FREQUENCY
The switching frequency (f
SW
) setpoint can be changed by
replacing the R9 resistor with a different value by using
following equation:
SW
f
R
500
,
92
9
=
where:
R9
is the frequency resistor in kΩ.
f
SW
is the switching frequency in kHz.
Table 3. Programming Frequency
R9 (kΩ)
Frequency (kHz)
308
300
132
700
92.5
1000
When the switching frequency (f
SW
) is changed, the L1, C7, C8,
R5, and C10 values must be recalculated and changed to ensure
stable operation (see the
ADP2442
data sheet for details on
external component selection).
