AMC1203 datasheet(16/23 Pages) TI

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SNR=1.76dB+6.02dB

ENOB

(2)

OSR

100

1000

sinc

sincfast

H(z)=

-OSR

-1

(1+z

)

-2OSR

(3)

SettlingTime( s)

sinc

sincfast

AMC1203

SBAS427 – FEBRUARY 2008

The effective number of bits (ENOB) is often used to

compare the performance of ADCs and delta-sigma

modulators. Figure 28 shows the ENOB of the

AMC1203 with different oversampling ratios. In this

data sheet, this number is calculated from the SNR

using following formula:

In motor-control applications, a very fast response

time for the over-current detection is required. The

time for full settling of the filter depends on its order

(that is, a sinc3 filter requires three data clocks for full

settling (with fDATA = fMOD/OSR). Therefore, for

over-current protection, filter types other than sinc3

might be a better choice; an alternative is the sinc2

filter. Figure 29 compares the settling times of

Figure 28. Measured Effective Number of Bits vs

different filter orders (sincfast is a modified sinc2

Oversampling Ratio

filter):

For more information, see application note SBAA094,

Combining the ADS1202 with an FPGA Digital Filter

for

Current

Measurement

Motor

Control

Applications, available for download at www.ti.com.

Figure 29. Measured Effective Number of Bits vs

Settling Time

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