EVAL-AD5933EB

Preliminary Technical Data

Rev. PrC | Page 20 of 32

The gain factor is then given by

GAIN FACTOR CALCULATION

Magnitude

Magnitude

Impedance

Code

Admittance

Factor

Gain

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

=

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

⎟

⎠

⎞

⎜

⎝

⎛

=

kΩ

100

1

1

The code in the Evaluation Board Source Code Extract section

for the impedance sweep is based on a single-point gain factor

calculation, which is determined at the midpoint sweep frequency

with a known impedance connected between VOUT and VIN.

The gain factor for this example is calculated by exciting the

calibration impedance using a 2 V p-p sinusoid with a frequency

of 30.750 kHz, a PGA setting of ×1, a 100 kΩ resistor connected

between VOUT and VIN, and a feedback resistor of 100 kΩ.

The magnitude of the real and imaginary components at the

calibration frequency is given by the formula:

Refer to the AD5933 data sheet for more details.

TEMPERATURE MEASUREMENT

The temperature sensor data is stored in a 14-bit, twos

complement format. For the conversion formula and more

details on the temperature sensor, see the AD5933 data sheet.

2

2

I

R

Magnitude

+

=

where R is the real component, and I is the imaginary

component of the calibration code.

Private Sub MeasureTemperature()

' The Digital temperature Result is stored over two registers as a 14 bit twos complement number.

' 92H <D15-D8> and 93H<D7 to D0>.

Dim TemperatureUpper As Long.

Dim TemperatureLower As Long

'Write xH90

to the control register to take temperature reading.

WritetToPart &H80, &H90

msDelay 5 'nominal delay

ReadbackStatusRegister = PortRead(&HD, &H8F)

ReadbackStatusRegister = ReadbackStatusRegister And &H1

'if a valid temperature conversion is complete, ignore this.

If ReadbackStatusRegister <> 1 Then

'loop to wait for temperature measurement to complete.

Do

ReadbackStatusRegister = PortRead(&HD, &H8F)

ReadbackStatusRegister = ReadbackStatusRegister And &H1

Loop Until (ReadbackStatusRegister = 1)

Form1.Label10.Caption = "Current Device Temperature"

MsgBox "Device Temperature Measurement Complete"

End If

' The Digital temperature Result is stored over two registers as a 14 bit twos complement number.

' 92H <D15-D8> and 93H<D7 to D0>.

TemperatureUpper = PortRead(&HD, &H92)

TemperatureLower = PortRead(&HD, &H93)

Temperature = TemperatureLower + (TemperatureUpper * 256)