Datasheet

Evaluation Board User Guide UG-456
Rev. 0 | Page 5 of 12
MODIFYING THE EVALUATION BOARD
The ADP2442-EVA LZ 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-EVA L Z 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
V6.0
R
R3R2
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
VV
R3R2
For example, to set the output regulation voltage of the
ADP2442-EVA L Z to 3.3 V, calculate the R2 and R3 values
as shown in the following equations:
kΩ10
μA60
V0.6
===
STRING
I
FB
V
R3
ΩΩ
k45.3
0.6V
V0.6V3.3
k10 =






−
×=






−
×=
FB
FB
OUT
V
VV
R3R2
When the output voltage of the ADP2442-EVAL Z 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).