MAX1729
To use a DC control signal to adjust the output voltage,
use the circuit shown in Figure 4. In this configuration,
V
OUT
is governed by the following equation:
The impedance looking into COMP is nominally 33kΩ.
A source output impedance of less than 500Ω is rec-
ommended. Also, ensure V
OUT
≤ 18V by keeping
V
COMP
above 0.6V.
Designing for External Feedback Mode
To solve for V
OUT
in external feedback mode, assume
the current into the FB pin is zero and the voltage at FB
is 1.228V. Then take the sum of the currents into FB
and solve for V
OUT
:
Using the following formulas, calculate the external
component values required for MAX1729 operation in
external feedback mode, as shown in Figure 3. An
example follows the formulas.
External Component Value Formulas
1) Given the maximum output voltage needed (V
MAX
),
choose the maximum feedback current and solve for
R1 (10µA to 30µA is recommended for maximum feed-
back current) as follows:
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
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