CS5529(1997) Просмотр технического описания (PDF) - Cirrus Logic

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CS5529
(Rev.:1997)

16-Bit, Programmable ∆Σ ADC with 6-Bit Latch

Cirrus Logic 

CS5529

FAQs

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+)-

(VAIN-) is the voltage between AIN+ and AIN-, f is either 256 or

32,768, and C is 32 pF. A typical input current for the higher ranges is

1.2 µA/V.

8) When reading the conversion data I get all zeroes no matter what the ana-

log signal is. Please explain why.

A: Check the voltage between pins 19 and 20 (VREF+ and VREF-). If it is

zero, the converter will compute all zeros because the digital output word

represents the ratio of the input signal to the voltage reference.

4

PI246PP1 OCT ‘97

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