MAX271ENG datasheet(9/16 Pages) AD

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Maxim Integrated

Digitally-Programmed, Dual

2nd-Order Continuous Lowpass Filter

MAX270/MAX271

Figure 1c. MAX271 Block Diagram—Pin-Strap Mode

Filter Programming

Cutoff Frequency

fC is the frequency of 3dB attenuation in the filter

response.

Table 1 shows how data pins D0–D6 allow programming

of 128 cutoff frequencies from 1kHz to 25kHz.

The equations for calculating fC from the programmed

code are as follows:

−

87.5

x1kHz

forcodes0 63

87.5 CODE

)

1kHz to3.57kHz

262.5

x1kHz for codes 64 127

137.5 CODE

kHz to kHz)

3.57

where CODE is the data on pins D0–D6 (0–127). D6 is

the most significant bit (MSB).

Actual cutoff frequencies are subject to some error for

each programmed code. Highest accuracy occurs at

CODE = 0 where filters are trimmed for a 1kHz cut-

off frequency. At higher codes, CODE vs. fC errors

increase; the frequency error at CODE = 127 {highest

code) remains typically within Q9.5%. This means that

the actual filter cutoff frequency, when programmed to

CODE = 127, falls between 22.63kHz and 27.38kHz.

DIRECT

CONTROL

D0-D6

17-23

INA

OUTA

T/H OUT

OUTB

A1*

V+

V-

GND

INB

CS* WR*

SHDN*

T/H*

A/B

TO GND OR V-

T/H

A0*

*PIN HAS NO FUNCTION IN PIN-STRAP MODE.

T/H*

PIN-STRAP

MODE

MAX270

MODE

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