CS5509(1995) View Datasheet(PDF) - Cirrus Logic

Part Name

Description

Manufacturer

CS5509
(Rev.:1995)

Single Supply, 16-Bit A/D Converter

Cirrus Logic 

the data sheet for information on reading data

from the serial port.

In the event the A/D conversion command

(CONV going positive) is issued during the con-

version state, the current conversion will be

terminated and a new conversion will be initi-

ated.

Voltage Reference

The CS5509 uses a differential voltage reference

input. The positive input is VREF+ and the

negative input is VREF-. The voltage between

VREF+ and VREF- can range from 1 volt mini-

mum to 3.6 volts maximum. The gain slope will

track changes in the reference without recalibra-

tion, accommodating ratiometric applications.

Analog Input Range

The analog input range is set by the magnitude

of the voltage between the VREF+ and VREF-

pins. In unipolar mode the input range will

equal the magnitude of the voltage reference. In

bipolar mode the input voltage range will equate

to plus and minus the magnitude of the voltage

reference. While the voltage reference can be as

great as 3.6 volts, its common mode voltage can

be any value as long as the reference inputs

VREF+ and VREF- stay within the supply volt-

ages VA+ and GND. The differential input

voltage can also have any common mode value

as long as the maximum signal magnitude stays

within the supply voltages.

The A/D converter is intended to measure dc or

low frequency inputs. It is designed to yield ac-

curate conversions even with noise exceeding

the input voltage range as long as the spectral

components of this noise will be filtered out by

the digital filter. For example, with a 3.0 volt

reference in unipolar mode, the converter will

accurately convert an input dc signal up to

3.0 volts with up to 15% overrange for 60 Hz

noise. A 3.0 volt dc signal could have a 60 Hz

12

CS5509

Unipolar Input

Voltage

>(VREF - 1.5 LSB)

VREF - 1.5 LSB

VREF/2 - 0.5 LSB

+0.5 LSB

<(+0.5 LSB)

Output

Codes

Bipolar Input

Voltage

FFFF >(VREF - 1.5 LSB)

FFFF

FFFE VREF - 1.5 LSB

8000

7FFF

-0.5 LSB

0001

0000 -VREF +0.5 LSB

0000 <(-VREF +0.5 LSB)

Note: Table excludes common mode voltage on the

signal and reference inputs.

Table 1. Output Coding

component which is 0.5 volts above the maxi-

mum input of 3.0 (3.5 volts peak; 3.0 volts dc

plus 0.5 volts peak noise) and still accurately

convert the input signal (XIN = 32.768 kHz).

This assumes that the signal plus noise ampli-

tude stays within the supply voltages.

The CS5509 converters output data in binary

format when converting unipolar signals and in

offset binary format when converting bipolar

signals. Table 1 outlines the output coding for

both unipolar and bipolar measurement modes.

Converter Performance

The CS5509 A/D converter has excellent linear-

ity performance. Calibration minimizes the

errors in offset and gain. The CS5509 device

has no missing code performance to 16-bits.

Figure 4 illustrates the DNL of the CS5509. The

converter achieves Common Mode Rejection

(CMR) at dc of 105 dB typical, and CMR at 50

and 60 Hz of 120 dB typical.

The CS5509 can experience some drift as tem-

perature changes. The CS5509 uses

chopper-stabilized techniques to minimize drift.

Measurement errors due to offset or gain drift

can be eliminated at any time by recalibrating

the converter.

DS125F1

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