ADuC7060
Table 37. Example Scenarios for Using Diagnostic Current Sources
Diagnostic Test
Detected
Measurement
Register Setting
ADC0DIAG[1:0] = 0
ADC0DIAG[1:0] = 1
Description
Convert ADC0/ADC1 as normal with
diagnostic currents disabled.
Enable a 50 μA diagnostic current
source on ADC0 by setting
ADC0DIAG[1:0] = 1. Convert ADC0 and
ADC1.
Normal Result
Expected differential result
across ADC0/ADC1.
Main ADC changes by
ΔV = +50 μA × R1. For
example, ~100 mV for R1 =
2 kΩ.
Fault Result
Short circuit.
Short circuit
between ADC0
and ADC1.
Short circuit
for Fault
Primary ADC reading ≈ 0 V
regardless of PGA setting.
Primary ADC reading ≈ 0 V
regardless of PGA setting.
between R1_a
and R1_b.
Convert ADC0 in single-ended mode
with diagnostic currents disabled.
Expected voltage on ADC0.
ADC0 open
circuit or R1
open circuit.
Primary ADC reading =
+full scale, even on the
lowest PGA setting.
ADC0DIAG[1:0] = 3
Enable a 50 μA diagnostic current
source on both ADC0 and ADC1 by
Primary ADC changes by ΔV
= 50 μA × (R1 ? R2); that is,
R1 does not
match R2.
Primary ADC reading >
10 mV.
setting ADC0DIAG[1:0] = 3. Convert
ADC0 and ADC1.
~10 mV for 10% tolerance.
Sinc3 Filter
The number entered into Bits[6:0] of the ADCFLT register sets
the decimation factor of the sinc3 filter. See Table 44 and Table 45
for further details on the decimation factor values.
The range of operation of the sinc3 filter (SF) word depends on
whether the chop function is enabled. With chopping disabled,
the minimum SF word allowed is 3 and the maximum is 127,
giving an ADC throughput range of 50 Hz to 2 kHz.
For details on how to calculate the ADC sampling frequency
based on the value programmed to the SF[6:0] in the ADCFLT
register, refer to Table 44 for more details.
ADC CHOPPING
The ADCs on the ADuC7060 implement a chopping scheme
whereby the ADC repeatedly reverses its inputs. Therefore, the
decimated digital output values from the sinc3 filter have a
positive and negative offset term associated with them. This
results in the ADC including a final summing stage that sums
and averages each value from the filter with previous filter
output values. This new value is then sent to the ADC data
MMR. This chopping scheme results in excellent dc offset and
offset drift specifications and is extremely beneficial in
applications where drift and noise rejection are required.
Programmable Gain Amplifier
The primary ADC incorporates an on-chip programmable gain
AVDD. They are individually configurable to give a current
range of 200 μA to 1 mA. The current step sizes are 200 μA.
These current sources can be used to excite an external resistive
bridge or RTD sensors. The IEXCON MMR controls the
excitation current sources. Bit 6 of IEXCON must be set to
enable Excitation Current Source 0. Similarly, Bit 7 must be set
to enable Excitation Current Source 1. The output current of
each current source is controlled by the IOUT[3:0] bits of this
register.
It is also possible to configure the excitation current sources to
output current to a single output pin, either IEXC0 or IEXC1,
by using the IEXC0_DIR and IEXC1_DIR bits of IEXCON. This
allows up to 2 mA to output current on a single excitation pin.
ADC Low Power Mode
The ADuC7060 allows the primary and auxiliary ADCs to be
placed in low power operating mode. When configured for this
mode, the ADC throughput time is reduced, but the power
consumption of the primary ADC is reduced by a factor of
about 4; the auxiliary ADC power consumption is reduced by a
factor of roughly 3. The maximum ADC conversion rate in low
power mode is 2 kHz. The operating mode of the ADCs is
controlled by the ADCMDE register. This register configures
the part for either normal mode (default), low power mode, or
low power plus mode. Low power plus mode is the same as low
power mode except that the PGA is disabled. To place the ADCs
in low power mode, the following steps must be completed:
amplifier (PGA). The PGA can be programmed through 10
different settings giving a range of 1 to 512. The gain is
controlled by the ADC0PGA[3:0] bits in the ADC0CON MMR.
Excitation Sources
The ADuC7060 contains two matched software configurable
current sources. These excitation currents are sourced from
?
?
?
ADCMDE[4:3]—Setting these bits enables normal mode,
low power mode, or low power plus mode.
ADCMDE[5]—Setting this bit configures the part for low
power mode.
ADCMDE[7]—Clearing this bit further reduces power
consumption by reducing the frequency of the ADC clock.
Rev. 0 | Page 35 of 100
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