aduc7032 Analog Devices, Inc., aduc7032 Datasheet - Page 65

• Manufacturer Part Number: aduc7032
• Description: Microconverter Integrated, Precision Battery Sensor
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
A factory or end-of-line calibration for the I-ADC would be a
2-step procedure:
1. Apply 0A current.
Configure the ADC in the required PGA setting etc. and write
to ADCMDE[2:0] to perform a System Zero-Scale Calibration.
This writes a new offset calibration value into ADC0OF.
2. Apply a Full-Scale current for the selected PGA setting.
Write to ADCMDE to perform a System Full-Scale Calibration.
This writes a new gain calibration value into ADC0GN.
Understanding the Offset and Gain Calibration
Registers
The output of the average block in the ADC signal flow
described earlier after the digital filter and before the Offset and
Gain scaling can be considered to be a fractional number with a
span, for a +/- Full-Scale input, of approx +/-0.75. The span is
less than +/-1.0 because there is attenuation in the modulator
to accommodate some over-range capacity on the input signal.
The exact value of the attenuation will vary slightly from part-
to-part, because of manufacturing tolerances.
The Offset Coefficient is read from the ADC0OF calibration
register. This value is a 16-Bit 2's complement number. The
range of this number, in terms of the signal chain, is effectively
+/-1.0. 1 LSB of the ADC0OF register is therefore not the same
as 1LSB of ADC0DAT.
A positive value of ADC0OF indicates that offset is subtracted
from the output of the filter, a negative value is added. The
nominal value of this register is 0x0000, indicating zero offset is
to be removed. The actual offset of the ADC may vary slightly
from part-to-part and at different PGA gains. The offset within
the ADC is minimized if the Chopping mode is active
(ADCFLT[15]=1).
The Gain Coefficient is a unitless scaling factor. The 16-Bit
value in this register is divided by 16384, and then multiplied
by the offset-corrected value. The nominal value of this register
equals 0x5555, which corresponds to a multiplication factor of
1.3333. This scales the nominal +/-0.75 signal to produce a full-
scale output signal of +/-1.0 which is checked for Overflow/
Underflow and converted to Two's Complement or Unipolar
mode as appropriate, before being output to the Data register.
The actual gain, and the required scaling coefficient for zero
gain error, varies slightly from part to part, and at different
PGA settings and in Normal / Low-Power-Mode. The value
downloaded into ADC0GN at power-on/reset represents the
scaling factor for a PGA Gain=1. There will be some level of
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gain error if this value is used at different PGA settings. User
code can over-write the calibration coefficients or run ADC
calibrations to correct the gain error at the current PGA setting.
In Summary, the simplified ADC transfer function can be
described as :
This equation is valid for Voltage/Temperature channel ADC.
For the Current Channel ADC,
where K is dependent on PGA gain setting and ADC mode.
Normal Mode:
Low Power Mode:
Low Power Plus Mode:
In Low-Power and Low-Power-Plus Mode, the K factor doubles
if (AVDD_Reg)/2 is used as the reference.
ADC DIAGNOSTICS
The ADuC7032 features diagnostic capability on all three
ADCs.
Current ADC Diagnostics
The ADuC7032 features the capability to detect Open Circuit
conditions on the application board. This is accomplished
using the two current sources on IIN+ and IIN-, which is
controlled via ADC0CON[14,13].
The use of both the IIN+ and IIN- current sources is shown in
Table 33.
To verify the current ADC is converting correctly, it is possible
to select an internal test voltage via ADC0CON[7,6]. Selecting
mode 10 results in the current ADC converting the Voltage
Reference, e.g. The Precision 1.2V Reference, divided by 136 for
PGA settings less than or equal to 128 and divided by
(1.0625*Gain) for PGA settings greater than 128.
ADCOUT
ADCOUT
PGA gains of 2 and 128 the K factor is 2. For PGA gain of 256
the K Factor is 4. For PGA gain of 512, the K factor is 8.
For PGA gains of 1,4,8,16,32 and 64 the K factor is 1. For
The PGA gain is set to 128 and the K factor is 32.
The K factor is 8.
VREF
VREF
VIN
VIN
K
ADCOF
*
ADCOF
*
ADCGNNOM
ADuC7032
*
ADCGN
ADCGNNOM
ADCGN