CS5464 datasheet(21/46 Pages) CIRRUS

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CS5464

DS682PP1

5.7 On-chip Temperature Sensor

The on-chip temperature sensor is designed to assist in

characterizing the measurement element over a desired

temperature range. Once a temperature characteriza-

tion is performed, the temperature sensor can then be

utilized to assist in compensating for temperature drift.

Temperature measurements are performed during con-

tinuous conversions and stored in the Temperature

. The Temperature Register (T) default is Cel-

sius scale (°C). The Temperature Gain Register (Tgain)

and Temperature Offset Register (Toff) are constant val-

ues allowing for temperature scale conversions.

The temperature update rate is a function of the number

of ADC samples. With MCLK = 4.096 MHz and K = 1

the update rate is:

The Cycle Count Register (N) must be set to a value

greater than one. Status bit TUP in the Status Register,

indicates when the Temperature Register is updated.

The Temperature Offset Register sets the zero-degree

measurement. To improve temperature measurement

accuracy, the zero-degree offset may need to be adjust-

ed after the CS5464 is initialized. Temperature-offset

calibration is achieved by adjusting the Temperature

Offset Register

(Toff) by the differential temperature

(

∆T) measured from a calibrated digital thermometer

and the CS5464 temperature sensor. A one-degree ad-

justment to the Temperature Register (T) is achieved by

adding 2.737649x10-4 to the Temperature Offset Regis-

ter

(Toff). Therefore,

if Toff = -0.094488 and ∆T = -2.0 (°C), then

or 0xF3D5BB (2’s compliment notation) is stored in the

Temperature Offset Register

(Toff).

To convert the Temperature Register (T) from a Celsius

scale (°C) to a Fahrenheit scale (°F) utilize the formula

Applying the above relationship to the CS5461A tem-

perature measurement algorithm

If Toff = -0.09504 and Tgain = 26.443 for a Celsius scale,

then

the

modified

values

are

Toff = -0.09017

(0xF47550) and Tgain = 47.6 (0x5F3333) for a Fahren-

heit scale.

5.8 Voltage Reference

The CS5464 is specified for operation with a +2.5 V ref-

erence between the VREFIN and AGND pins. To utilize

the on-chip 2.5 V reference, connect the VREFOUT pin

to the VREFIN pin of the device. The VREFIN can be

used to connect external filtering and/or references.

5.9 System Initialization

Upon powering up, the digital circuitry is held in reset

until the analog voltage reaches 4.0 V. At that time, an

eight-XIN-clock-period delay is enabled to allow the os-

cillator to stabilize. The CS5464 will then initialize.

A hardware reset is initiated when the RESET pin is as-

serted with a minimum pulse width of 50 ns. The RE-

SET signal is asynchronous, with a Schmitt-trigger

input. Once the RESET pin is de-asserted, an

eight-XIN-clock-period delay is enabled.

A software reset is initiated by writing the command

0x80. After a hardware or software reset, the internal

registers (some of which drive output pins) will be reset

to their default values. Status bit DRDY in the Status

indicates the CS5464 is in its active state and

ready to receive commands.

5.10 Power-down States

The CS5464 has two power-down states, Stand-by and

Sleep

. In the stand-by state all circuitry except the volt-

age reference and crystal oscillator is turned off. To re-

turn the device to the active state, a power-up command

is sent to the device.

In Sleep state, all circuitry except the instruction decod-

er is turned off. When the power-up command is sent to

the device, a system initialization is performed (See

Section 5.9 System Initialization on page 21).

5.11 Oscillator Characteristics

XIN and XOUT are the input and output of an inverting

amplifier configured as an on-chip oscillator, as shown

in Figure 11. The oscillator circuit is designed to work

2240 samples

MCLK K

⁄

() 1024

⁄

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

0.56 sec

off

∆T 2.737649 10

–

⋅

()

off

0.094488

–

2.0

–

2.737649

–

⋅

()

0.09504

–

---C

17.7778

()

〈〉

--- T

gain

⎝⎠

⎛⎞ TC

〈〉

off

17.7778

2.737649

–

⋅

()

⎝⎠

⎛⎞

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