CS5509-ASZ datasheet(12/23 Pages) CIRRUS

12 / 23 page

CS5509

DS125F2

in the reference without recalibration, accommo-

dating 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 voltages VA+ and GND.

The differential input voltage can also have any

common mode value as long as the maximum sig-

nal magnitude stays within the supply voltages.

The A/D converter is intended to measure dc or low

frequency inputs. It is designed to yield accurate

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 in-

put dc signal up to 3.0volts with up to 15% over-

range for 60Hz noise. A 3.0volt dc signal could

have a 60Hz component which is 0.5volts above

the maximum 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 amplitude stays

within the supply voltages.

The CS5509 converters output data in binary for-

mat when converting unipolar signals and in offset

binary format when converting bipolar signals. Ta-

ble 1 outlines the output coding for both unipolar

and bipolar measurement modes.

Converter Performance

The CS5509 A/D converter has excellent linearity

performance. Calibration minimizes the errors in

offset and gain. The CS5509 device has no missing

code performance to 16-bits. Figure4 illustrates the

DNL of the CS5509. The converter achieves Com-

mon Mode Rejection (CMR) at dc of 105dB typi-

cal, and CMR at 50 and 60Hz of 120dB typical.

The CS5509 can experience some drift as tempera-

ture 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.

Analog Input Impedance Considerations

The analog input of the CS5509 can be modeled as

illustrated in Figure 5. Capacitors (15 pF each) are

used to dynamically sample each of the inputs

(AIN+ and AIN-). Every half XIN cycle the switch

alternately connects the capacitor to the output of

the buffer and then directly to the AIN pin. When-

ever the sample capacitor is switched from the out-

put of the buffer to the AIN pin, a small packet of

charge (a dynamic demand of current) is required

from the input source to settle the voltage of the

sample capacitor to its final value. The voltage on

the output of the buffer may differ up to 100 mV

from the actual input voltage due to the offset volt-

age of the buffer. Timing allows one half of a XIN

clock cycle for the voltage on the sample capacitor

to settle to its final value.

Unipolar Input

Voltage

Output

Codes

Bipolar Input

Voltage

> (VREF - 1.5 LSB)

FFFF

> (VREF - 1.5 LSB)

VREF - 1.5 LSB

VREF/2 - 0.5 LSB

-0.5 LSB

+0.5 LSB

-VREF + 0.5 LSB

< (+0.5 LSB)

0000

< (-VREF + 0.5 LSB)

Note: Table excludes common mode voltage on the

signal and reference inputs.

Table 1. Output Coding

FFFF

FFFE

----------------

8000

7FFF

---------------

0001

0000

-------------

CS5509-ASZ 数据表(PDF) 12 Page - Cirrus Logic

CS5509-ASZ 数据表(HTML) 12 Page - Cirrus Logic

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

数据表下载