DIO221X

Version 1.1, Feb 2024

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© 2024 DIOO MICROCIRCUITS CO., LTD.

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9.3. Input filtering

One possible location for filtering is at the output of the DIO221X series, in which case the output

impedance of the internal buffer increases. Adding a filter at the input pins of the DIO221X series is a

better option although the input impedance makes the input filtering more complicated as shown in Figure

9. To minimize the initial shift in gain and effects of tolerance, use the lowest resistor values. Equation (1)

tells the effect on initial gain.

)

R

+

5kΩ

5kΩ

×

(100

-

100

=

%

Error

Gain

FILTER

(1)

Figure 9. Input filter

Calculate the total effect on gain error by substituting the 5 kΩ term with 5 kΩ - 30% or 5 kΩ + 30%. Put

the tolerance extremes of RFILTER into equation (1). For instance, two resistors of 100 Ω 1% near the input

pins, making a gain error of 1.96%. The worst case approach is using an internal 5 kΩ resistor and RFILTER

+ 3%, which will offer an error gain larger than the normal value.

The specified accuracy of the DIO221X is another important factor to consider apart from these tolerances.

Geometric-mean and root-sum-square mean are another two recommended ways to calculate the

variations of accuracy.

10.Layout

Use four wire connection, also known as Kelvin connection, to connect the input pins and the sensing

resistor together so as to ensure only the current sensing resistance is detected. Inappropriate layout

often results in additional resistance between the input pins, causing erroneous measuring. Locate the

power-supply bypass capacitor, 0.1 μF recommended, as close as possible to the VS and GND pins. Use

an additional decoupling capacitor to lessen the impacts of noisy or high-impedance power supplies.