CS5504-BS View Datasheet(PDF) - Cirrus Logic

Part Name

Description

MFG CO.

CS5504-BS

Low Power, 20-Bit A/D Converter

Cirrus Logic 

CS5504

CS5504

ated from the standby state, there may be up to

two XIN clock cycles of uncertainty as to when

conversion actually begins. This is because the

internal logic operates at one half the external

clock rate and the exact phase of the internal

clock may be 180° out of phase relative to the

XIN clock. When a new conversion is initiated

from the standby state, it will take up to two

XIN clock cycles to begin. Actual conversion

will use 1624 clock cycles before DRDY goes

low to indicate that the serial port has been up-

dated. See the Serial Interface Logic section of

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 CS5504 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 for the A/D. 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

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 CS5504 converters output data in binary

format when converting unipolar signals and in

offset binary format when converting bipolar

signals. Table 2 outlines the output coding for

both unipolar and bipolar measurement modes.

Unipolar Input

Voltage

>(VREF - 1.5 LSB)

VREF - 1.5 LSB

VREF/2 - 0.5 LSB

+ 0.5 LSB

<(+ 0.5 LSB)

Output

Codes

FFFFF

FFFFF

FFFFE

80000

7FFFF

00001

00000

00000

Bipolar Input

Voltage

>(VREF - 1.5 LSB)

VREF - 1.5 LSB

-0.5 LSB

-VREF + 0.5 LSB

<(VREF + 0.5 LSB)

Note: Table excludes common mode voltage on the

signal and reference inputs.

Table 2. Output Coding

12

DS126F21

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