Adc Initialization; Adc Calibration - Analog Devices ADuCM356 Reference Manual

Reference Manual
ADC CIRCUIT
}
void CalculateTemp(void) // PGA GAIN of 1.5x
assumed
{
fTemp = (float)(( TEMP_RE►
SULT/(1.5*8.13))-273.15); // ((Temperature
reading/(PGA_Gain*8.13)-273.15
}
In Figure 12, the base emitter voltage (VBE) of the transistor is
connected to 16 different current sources. The transistor labeled
VBE_REF is a reference transistor. The base emitter voltage of
both transistors varies with temperature. This variation is used to
calculate the die temperature.
The voltage of VBE is measured relative to the voltage of
VBE_REF via the ADC as a differential voltage. The conversion
result is placed in the ADCDAT or SINC2DAT register, depending
on the digital filter settings used. To select the Temperature Sensor
1 ADC inputs, set the ADCCON register to the following values:
ADCCON, Bits[12:8] = 010101 selects the VBE_REF voltage as
►
the ADC negative input.
ADCCON, Bits[5:0] = 001011 selects the VBE voltage as the
►
ADC positive input.
The 16 switches connecting different current sources to the emitter
terminal of the VBE transistor are controlled by the TEMPCON1
Bits[15:0]. Providing separate current sources to the VBE transistor
means that a more accurate base emitter voltage can be extracted.
To extract the base emitter voltage, take the following steps:
1. Close each switch individually and measure these 16 VBE vol-
tages individually. Calculate the average of 16 measurements to
give an overall voltage (VBE1).
2. Close the switches in groups of four and measure these four
VBE voltages individually. Calculate the average of four meas-
urements to give an overall voltage (VBE2).
3. Close all switches to connect all current sources to the VBE
transistor and measure the VBE voltage to obtain VBE3.
Equation 5 calculates the final temperature sensor value. The value
2768.231 is calculated using the charge of an electron (1.602 ×
–19
10 C) and the Boltzmann constant (1.381 × 10
analog.com
Temperature Sensor 1
A second backup temperature sensor is provided on the
ADuCM356 analog die for functional safety purposes. Only use
Temperature Sensor 1 to crosscheck the Temperature Sensor 0
channel. To calculate the die temperature with the Temperature
Sensor 1 channel, 21 different ADC measurements are required.
Figure 12. Temperature Sensor 1 Channel Overview
T(°C) = 2768.231 × (4(VBE2 – VBE1) – (VBE3 – VBE2)) –
273.15

ADC INITIALIZATION

The following steps are required to initialize the ADC:
1. Power up the ADC by writing to the ADCEN bit of the AFECON
2. Configure the ADC input buffers as per the recommendations
3. Configure the PGA gain setting as required. Write to ADCCON,
4. Configure the ADC update rate by writing to ADCFILTERCON.
5. Select the ADC positive and negative input channels by config-
6. If ADC interrupts are required, enable the interrupts by setting

ADC CALIBRATION

Because of the multiple input types of the ADuCM356, there are
multiple offset and gain calibration options. The ADC must be
recalibrated when switching from low-power mode to high-power
mode, regardless of the gain change. For optimal performance,
–23 calibrate the ADC in low-power mode and high-power mode, if both
).
power modes are used. An error occurs in the high-speed TIA
offset and gain when switching from low power to high power.
register.
for low-power or high-power mode.
pADI_AFE->ADCBUFCON = 0x005F3D04; // for
Low Power mode, input signals <80 kHz
pADI_AFE->ADCBUFCON = 0x005F3D0F; // for
high Power mode, input signals >80 kHz
Bits[18:16]. Setting these bits to 001 configures the PGA for a
gain of 1.5.
If the sinc2 filter is required, also write to AFECON, Bit 16.
uring ADCCON, Bits[12:0].
the required ADC bits in the ADCINTIEN register. Enable the
ADC global interrupt to the Cortex-M3 core.
ADuCM356
(5)
Table
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