A2F200M3F-FGG484 Actel, A2F200M3F-FGG484 Datasheet - Page 116

• Manufacturer Part Number: A2F200M3F-FGG484
• Description: ACLA2F200M3F-FGG484 SMART FUSION MIX SIG
• Manufacturer: Actel

Pin Descriptions
User-Defined Supply Pins
5 - 4
Name
VAREF0
VAREF1
VAREF2
VAREFOUT
Type
Input
Input
Input
Out
Polarity/Bus
Size
1
1
1
1
Analog reference voltage for first ADC
The SmartFusion device can be configured to generate a 2.56 V internal
reference that can be used by the ADC. While using the internal
reference, the reference voltage is output on the VAREFOUT pin for use
as a system reference. If a different reference voltage is required, it can
be supplied by an external source and applied to this pin. The valid range
of values that can be supplied to the ADC is 1.0 V to 3.3 V. When
VAREF0 is internally generated, a bypass capacitor must be connected
from this pin to ground. The value of the bypass capacitor should be
between 3.3 µF and 22 µF, which is based on the needs of the individual
designs. The choice of the capacitor value has an impact on the settling
time it takes the VAREF0 signal to reach the required specification of 2.56
V to initiate valid conversions by the ADC. If the lower capacitor value is
chosen, the settling time required for VAREF0 to achieve 2.56 V will be
shorter than when selecting the larger capacitor value. The above range
of capacitor values supports the accuracy specification of the ADC, which
is detailed in the datasheet. Designers choosing the smaller capacitor
value will not obtain as much margin in the accuracy as that achieved with
a larger capacitor value. See the Analog-to-Digital Converter (ADC)
section in the
information. Actel recommends customers use 10 µF as the value of the
bypass capacitor. Designers choosing to use an external VAREF0 need to
ensure that a stable and clean VAREF0 source is supplied to the VAREF0
pin before initiating conversions by the ADC. To use the internal voltage
reference, you must connect the VAREFOUT pin to the appropriate ADC
VAREFx input—either the VAREF0 or VAREF1 pin—on the PCB.
Analog reference voltage for second ADC
See
Analog reference voltage for third ADC
See
Internal 2.56 V voltage reference output. Can be used to provide the two
ADCs with a unique voltage reference externally by connecting
VAREFOUT to both VAREF0 and VAREF1. To use the internal voltage
reference, you must connect the VAREFOUT pin to the appropriate ADC
VAREFx input—either the VAREF0 or VAREF1 pin—on the PCB.
"VAREF0"
"VAREF0"
SmartFusion Programmable Analog User’s Guide
R e vi s i o n 3
above for more information.
above for more.
Description
for more