AMC7823 Datasheet, PDF (25/48 Pages) Texas Instruments – ANALOG MONITORING AND CONTROL CIRCUIT

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AMC7823
SLAS453A – APRIL 2005 – REVISED OCTOBER 2005
SS
WRITE ADC
CONTROL Register
1st Internal
Trigger
MOSI
WRITE ADC
CONTROL Register
2nd Internal
Trigger
SS
WRITE ADC
CONTROL Register
Internal Trigger
MOSI
DAV
DAV
2ms
1st Conversions,
2nd Conversions,
[SA3:SA0] to [EA3:EA0] [SA3:SA0] to [EA3:EA0]
Figure 42. Internal Trigger, Direct-Mode
CONVERT
Rising Edge
Starts Conversions
1st Trigger
2nd Trigger
1st Round of
2nd Round of
Conversions,
Conversions,
[SA3:SA0] to [EA3:EA0] [SA3:SA0] to [EA3:EA0]
Figure 43. Internal Trigger, Auto-Mode
3rd Trigger
DAV
1st Conversions, of
2nd Conversions,
3rd Conversions,
Analog Inputs, From _{[SA3:SA0] to [EA3:EA0] [SA3:SA0] to [EA3:EA0]}
[SA3:SA0] to [EA3:EA0]
Figure 44. External Trigger
Analog Input Out-of-Range Detection (see Analog Input Out-of-Range Alarm Section)
The first four analog inputs of the group defined by the bits [SA3:SA0] and [EA3:EA0] are implemented with
out-of-range detection. When an input is out of the preset range, the corresponding alarm flag, bit ALR-n of the
ALR (Alarm) Register is set. If any of the four inputs are out of range, the global out-of-range pin GALR goes low.
Four GPIO pins (GPIO-0, GPIO-1, GPIO-2 and GPIO-3) can be configured as out-of-range indicators for each of
the first four analog inputs. See the Analog Input Out-of-Range Alarm and Digital I/O sections for more details.
Full-Scale Range of Analog Input
The full-scale range of the analog input is 2 × V_REF, but must not exceed the supply value AV_DD. Input saturation
can occur if the analog input exceeds this value.
The internal reference or an externally applied reference may be used as V_REF. The bit SREF in the AMC
Status/Configuration Register controls the selection of the internal reference. When SREF = 0 (power-up default
condition), the internal reference is selected and is internally applied through a 10-kΩ resistor to pin 21. When
SREF = 1, the internal reference is disconnected from pin 21, and an external reference may be applied. See
Figure 48.
Table 4 shows the configuration of the ADC input range.
BIT
GREF
0
1
Don't
care
BIT
SREF
0
0
1
Table 4. Configuration of ADC Input Range
ADC INPUT
RANGE
0 to 2.5 V
0 to 5 V
0 to 2 × V_REF
DESCRIPTION
Internal reference, 1.25 V
Internal reference, 2.5 V, AV_DD = 5 V only
External reference V_REF. 2 × V_REF must not be greater than AV_DD.
Set SREF = 1 when applying external reference.
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