MAX17843ACB datasheet(33/131 Pages) MAXIM

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Infinite Impulse Response Filtering (IIR Filter):

To augment the accuracy performance, an IIR filtering

scheme is implemented where the results of the cell volt-

ages are filtered after the oversampling. The IIR filter is

implemented by the simple equation below:

Y(n) = FC x X(n) + (1 - FC) x Y(n-1)

where FC = filter coefficient, user-selectable 3 bits.

The default value is b’010, which has a weight of 3/8:

● X (n) = 3/8

● Y (n-1) = 5/8

The detailed filter coefficient settings are mentioned in the

DEVCFG1 register. The filter can be turned off by setting

the coefficient bits to b’111. The smaller that coefficient

is, the more the history, represented by Y (n-1) outputs in

the equation, so it’s a tradeoff between response times to

change in input value versus the noise attenuation. Refer

to the application note in detail for how the filter affects the

accuracy performance of MAX17843.

Two new bits are added for the control of the data flow

through the filter:

1) AMEND Filter (AMENDFILT) bit

2) Read Filter (RDFILT) bit

AMENDFILT is in SCANCTRL register 0x13.

This bit when set to ‘1’ enables the automatic transfer

of the new ADC conversion from the ALUn to CELLn

registers through the IIR filter at the end of the scan. The

default value is ‘0’, which keeps the scan conversion data

in the ALUn register as an unfiltered result.

Figure 11. IIR Filter Block Diagram

Table 8. AMENDFILT Bit

AMENDFILT BIT

FUNCTIONALITY AND RECOMMENDED USAGE

No transfer of the ADC conversion result from ALUn to CELLn registers. Unfiltered data is stored in ALUn

registers at the end of the scan. This bit should be set to ‘0’ during any diagnostic conversion such as open-

sense wire, or using balancing switches.

Automatic transfer of the ADC conversion result from ALUn to CELLn registers at the end of the scan

through the IIR filter. Instantaneous unfiltered data is available in ALUn registers while the filtered data is

stored in the CELLn registers. This bit should be set to ‘1’ during normal cell-voltage measurements.

COMBINATIONAL

LOGIC

X(n)

INTERNAL

Y(n)

USER

Y(n-1)

IIR FILTER LOGIC

DIAGRAM

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

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