Datasheet

ADP2441-EVALZ User Guide UG-407
Rev. 0 | Page 5 of 12
MODIFYING THE EVALUATION BOARD
The ADP2441 evaluation board is provided fully assembled
and tested for proper operation. The ADP2441-EVAL Z has a
fixed 5 V output voltage.
CHANGING THE OUTPUT VOLTAGE
The ADP2441-EVA L Z output regulation voltage is set by a
resistive voltage divider consisting of Resistors R2 and R3.
Resistor R2 corresponds to the R
TOP
resistor in the data sheet
and Resistor R3 corresponds to the R
BOTTOM
resistor in the data
sheet. The output regulation voltage is determined by the
equation






+
×=
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 ADP2441-
EVA LZ to 3.3 V, calculate the value of Resistors R2 and R3 as
shown in the following equations:
kΩ10
μA60
V0.6
===
STRING
I
FB
V
R3
ΩΩ k3.45
V6.0
V6.0V3.3
k10 =






−
×=






−
×=
FB
FB
OUT
V
VV
R3R2
Note that when the output voltage of ADP2441-EVA L Z is
changed, the output capacitors (C7 and C8), inductor (L1), and
compensation components (R5 and C10) should be recalculated
and changed according to the Application Information section
in the ADP2441 data sheet to ensure stable operation.
Table 1. 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
) set point can be changed by
replacing Resistor R9 with a different value 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 2. Programming Frequency
R9 (kΩ) Frequency (kHz)
308 300
132 700
92.5 1000
Note that when the switching frequency (fSW) is changed,
to ensure stable operation, the values of Inductor L1, C7, C8
(output capacitors), and R5, C10 (compensation components)
must be recalculated and changed (see the ADP2441 data sheet
for details on external component selection).
CHANGING THE SOFT START TIME
The soft start time of the ADP2441 on the evaluation board is
programmed to 6 ms. To change the soft start time, t
SS
, replace
Capacitor C11 with a different capacitor value using the
following equation:
SS
REF
SS
t
V
I
C11 ×=
where:
V
REF
is the internal reference voltage and equals 0.6 V.
I
SS
is the soft start current and equals 1 μA.
C11 is the soft start capacitor value.
t
SS
is the soft start time