CS5540-AS datasheet(12/22 Pages) CIRRUS

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CS5540

DS503PP1

2.3 Power Supply Arrangements

The CS5540 is designed to operate with a total sup-

ply voltage of 3.0 V ± 5%. For maximum flexibili-

ty, separate pins are provided for VA+, VA-, VD+,

and DGND, which is especially useful with

ground-referenced input signals.

Figure 7 illustrates the CS5540 connected with a

single +3.0 V supply for both the analog and digital

sections.

2.4 Clock Generator

The CS5540 includes an oscillator circuit which

can be connected with an external crystal to pro-

vide the master clock for the chip. The chip is de-

signed to operate using a low-cost 32.768 kHz

“tuning fork” type crystal. One lead of the crystal

should be connected to OSC1 and the other to

OSC2. A 10 megohm resistor is required in parallel

with the crystal. Lead lengths should be minimized

to reduce stray capacitance. Note that the converter

will operate with an external (CMOS compatible)

clock with frequencies up to 40kHz, applied to the

OSC1 pin.

2.5 Serial Port Interface

The CS5540’s serial interface consists of three con-

trol lines: CS, SDO, and SCLK.

CS, Chip Select, is the control line which enables

access to the serial port. If the CS pin is tied to logic

0, the port can function as a three wire interface.

SDO, Serial Data Out, is the data signal used to

transfer output data from the converters. The SDO

output will be held at high impedance any time CS

is at logic 1.

SCLK, Serial Clock, is the serial bit-clock which

controls the shifting of data to or from the ADC’s

serial port. The CS pin must be held at logic 0 be-

fore SCLK transitions can be recognized by the

port logic. To accommodate opto-isolators, SCLK

is designed with a Schmitt-trigger input.

2.6 Input Channel Selector

CHS, the Channel Select input, permits the user to

select between AIN1 and AIN2 for data conver-

sions. When CHS = 0, AIN1 is converted. When

CHS = 1, AIN2 is converted. Note that since the

converter continuously converts the input selected

Figure 7. CS5540 Configured with a single +3.0 V Supply

OSC2

VD+

VA+

VREF+

VREF-

DGND

AIN1+

SCLK

SDO

CS5540

OSC1

+3.0 V

Analog

Optional Clock

Source

Serial

Data

Interface

5 kHz ~ 40 kHz

AIN1-

VA-

0.1

µF

0.1

µF

Ω

AIN2+

AIN2-

Voltage

Reference

CHS

Supply

Analog

Signal

Sources

Channel

Selection

10 M

Ω

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