TC1796
Peripheral Units (Vol. 2 of 2)
Fast Analog-to-Digital Converter (FADC)
User’s Manual 26-6 V2.0, 2007-07
FADC, V2.0
• FAINxN = 0 V: FADC conversion result is 768
• FAINxN = 3.3 V: FADC conversion result is 256
To cover the full range of the measurement result in this single-ended measurement
mode, a gain of 2 must be selected (ACRx.GAIN = 01
B
). With gain = 2, the FADC will
deliver conversion results as follows:
• FAINxN = 0 V: FADC conversion result is 1023
• FAINxN = 3.3 V: FADC conversion result is 0
The voltage at the disconnected positive analog input FAINxP has no influence on the
conversion result.
Configuration 2 (ACRx.ENP = 1 and ACRx.ENN = 0)
This configuration enables the single-ended measurement mode for FAINxP -
V
VAREF
/2.
The negative analog input FAINxN is disconnected and in a high impedance state. The
positive analog input FAINxP is connected to the channel amplifier (input impedance is
determined by Rp). The negative input of the channel amplifier is connected to V
FAREF
/2
(1.65 V with V
FAREF
= 3.3 V). If the voltage at the positive input FAINxP varies, the FADC
will deliver conversion results as follows (gain = 1 selected by ACRx.GAIN = 00
B
):
• FAINxP = 0 V: FADC conversion result is 256
• FAINxP = 3.3 V: FADC conversion result is 768
To cover the full range of the measurement result in this single-ended measurement
mode, a gain of 2 must be selected (ACRx.GAIN = 01
B
). With gain = 2, the FADC will
deliver conversion results as follows:
• FAINxP = 0 V: FADC conversion result is 0
• FAINxP = 3.3 V: FADC conversion result is 1023
The voltage at the disconnected negative analog input FAINxN has no influence on the
conversion result.
Configuration 3 (ACRx.ENP = ACRx.ENN = 1)
This configuration enables the differential measurement mode for FAINxP - FAINxN.
Both analog inputs, FAINx.N and FAINxP, are connected to the channel amplifier inputs.
Their impedances are determined by Rn and Rp. The full measurement range is
available.
Table 26-1 provides a summary of the conversion results that are available at the
different measurement modes. This table assumes a reference voltage of
V
FAREF
=3.3V.
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