CS5525(1998) Просмотр технического описания (PDF) - Cirrus Logic

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CS5525
(Rev.:1998)

16-Bit/20-Bit ∆Σ Multi-Range ADC with 4-Bit Latch

Cirrus Logic 

CS5525 CS5526

FAQs

A: The input bandwidth is limited to 1/2 the selected output word rate due to

the Nyquist theory of sampling. Example: With the default 15 Hz output

word rate the available signal bandwidth of the ADC is 7.5 Hz.

5) What is recommended if I need more or less bandwidth than is provided

by the on-chip digital filter?

A: Use an external clock between 30 KHz and 100 KHz to scale the digital

filters corner frequency accordingly. Example: Using a 3x clock =

3x32.768 kHz = 3 x the word rate = 3 x 3.76 Hz to 3 x 202 Hz = 11.47 Hz

to 616 Hz.

6) How fast can the converter shift data from its serial port?

A: Up to 2 Mhz.

7) How does the instrumentation amplifier’s chopping frequency affect the

converter’s input impedance and input current?

A: The input impedance of the converter is a dynamic impedance and

depends on whether the instrumentation amplifier is engaged or not. For

the lower ranges (25 mV, 55 mV, 100 mV), the instrumentation amplifier

is engaged setting the input impedance to 1/fC (where C is 2 pF, and f is

the chopping frequency, either 256 or 32,768). A typical input impedance

for the lower ranges is 1900 MW (with f = 256, and C = 2 pF). For the

higher ranges (1 V, 2.5 V, and 5 V), the amplifier is bypassed leaving an

equivalent input impedance of 1/fC where C is 32 pF and f is either 256

or 32,768. A typical input impedance for the higher ranges is 120 MW

(with f = 256 and C = 2 pF).

The input current is a dynamic current and also depends on whether the

instrumentation amplifier is engaged or not. For the lower ranges

(25 mV, 55 mV, 100 mV), the input current is fVosC (where Vos is the

offset of the instrumentation amplifier, typically less than 40 mV, f is the

chopping frequency, either 256 or 32,768, and C is 2 pF). A typical input

current for the lower ranges is 100 pA. For the higher ranges (1 V, 2.5 V,

and 5 V), the input current is [(VAIN+)-(VAIN-)]fC where (VAIN+)-

4

PI202PP3 JAN ‘98

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