AD5933 datasheet(9/20 Pages) AD

9 / 20 page

Preliminary Technical Data

AD5933

Rev. PrA | Page 9 of 20

Figure 8.

The DFT algorithm is represented by

X(f) = SUM x(n)[Cos(n)-jSine(n)]

Both the real and Imaginary data register have 15 bits of data

and one sign bit. The 15 bits of data are in 2’s compliment

format. The magnitude of the signal can be represented by

Magnitude =

R + I

This magnitude that’s returned is a scaled valued of the actual

complex impedance measured. The multiplication factor

between the magnitude returned and the actual impedance is

called the GAIN FACTOR. The user needs to then calculate this

GAIN FACTOR value and use it for calibration in the system.

TEMPERATURE SENSOR

The temperature sensor is a 13-bit digital temperature sensor

with a 14th bit that acts as a sign bit. The block houses an on-

chip temperature sensor, a 13-bit A/D converter and a reference

circuit. The A/D converter section consists of a conventional

successive-approximation converter based around a capacitor

DAC.

The on-chip temperature sensor allows an accurate measure-

ment of the ambient device temperature to be made. The

specified measurement range of the sensor is −40°C to +150°C.

At +150°C. The structural integrity of the device starts to

deteriorate when operated at voltage and temperature

maximum specifications.

Temperature Conversion Details

The conversion clock for the part is internally generated; no

external clock is required except when reading from and writing

to the serial port. In normal mode, an internal clock oscillator

runs an automatic conversion sequence. During this automatic

conversion sequence, a conversion is initiated every 1 second. At

this time, the part powers up its analog circuitry and performs a

temperature conversion. This temperature conversion typically

takes 800 µs, after which time the analog circuitry of the part

automatically shuts down. The analog circuitry powers up again

when the 1 second timer times out and the next conversion

begins. The result of the most recent temperature conversion is

always available in the serial output register because the serial

interface circuitry never shuts down.

The temperature sensor block will default to a power-down

state. To perform a temperature measurement a command is

written to the control register. After the temperature operation

is complete, the block automatically powers down until the next

temperature command is issued.

In normal conversion mode, the internal clock oscillator is reset

after every read or write operation. This causes the device to

start a temperature conversion, the result of which is typically

available 800 µs later. Similarly, when the part is taken out of

shutdown mode, the internal clock oscillator is started and a

conversion is initiated. The conversion result is available 800 µs

later, typically. Reading from the device before a conversion is

complete causes the block to stop converting; the part starts

again when serial communication is finished.

Temperature Value Register

The temperature value register is a 16-bit read-only register that

stores the temperature reading from the ADC in 13-bit twos

complement format plus a sign bit. The two MSB bits are don’t

cares. DB13 is the sign bit. The ADC can theoretically measure a

255°C temperature span. The internal temperature sensor is

guaranteed to a low value limit of –40°C and a high limit of

+150°C.

Table 4. Temperature Data Format

Temperature

Digital Output DB13…DB0

−40°C

11, 1011 0000 0000

−30°C

11, 1100 0100 0000

−25°C

11, 1100 1110 0000

−10°C

11, 1110 1100 0000

−0.03125°C

11, 1111 1111 1111

0°C

00, 0000 0000 0000

+0.03125°C

00, 0000 0000 0001

+10°C

00, 0001 0100 0000

+25°C

00, 0011 0010 0000

+50°C

00, 0110 0100 0000

+75°C

00, 1001 0110 0000

+100°C

00, 1100 1000 0000

+125°C

00, 1111 1010 0000

+150°C

01, 0010 1100 0000

Temperature Conversion Formula

Positive Temperature = ADC Code(d)/32

Negative Temperature = (ADC Code*(d) – 16384)/32

*Using all 14 bits of the data byte, includes the sign bit.

Negative Temperature = (ADC Code(d)* – 8192)/32

*DB13 (sign bit) is removed from the ADC code

AD5933 Datasheet(PDF) 9 Page - Analog Devices

AD5933 Datasheet(HTML) 9 Page - Analog Devices

Html Pages

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

Datasheet Download

Link URL