CS5351

DS565PP2

9

3.5

High Pass Filter and DC Offset Calibration

The operational amplifiers in the input circuitry driving the CS5351 may generate a small DC offset into

the A/D converter. The CS5351 includes a high pass filter after the decimator to remove any DC offset

which could result in recording a DC level, possibly yielding "clicks" when switching between devices in

a multichannel system.

The high pass filter continuously subtracts a measure of the DC offset from the output of the decimation

filter. If the HPF pin is taken high during normal operation, the current value of the DC offset register is

frozen and this DC offset will continue to be subtracted from the conversion result. This feature makes it

possible to perform a system DC offset calibration by:

1) Running the CS5351 with the high pass filter enabled until the filter settles.See the Digital Filter Char-

acteristics for filter settling time.

2) Disabling the high pass filter and freezing the stored DC offset.

A system calibration performed in this way will eliminate offsets anywhere in the signal path between the

calibration point and the CS5351.

3.6

Overflow Detection

The CS5361 includes overflow detection on both the left and right channels. This time multiplexed infor-

mation is presented as open drain, active low on pin 15, OVFL. The OVFL_L and OVFL_R data will go

to a logical low as soon as an overrange condition in either channel is detected. The data will remain low

VQ

10k

Ω

+

634

Ω

634

Ω

91

Ω

91

Ω

+

-

-

270 0 pF

470 p F

470 p F

CO G

CO G

100 u F

100 u F

C S 53 51 A I N L

C S 53 51 A I N R

AI N L

AI N R

CO G

10k

Ω

2 700 p F

CO G

Figure 3. CS5351 Recommended Analog Input Buffer