0000
1100
1101
1110
1111
0000
0001
0010
0011
1100
1101
1110
1111
CESHORT
Sampling capacitor, C
S
Analog Inputs
COMP_E Operation
918
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Comparator E (COMP_E) Module
Figure 35-2. Comparator_E Sample-And-Hold
The required sampling time is proportional to the size of the sampling capacitor R
S
, the resistance of the
input switches in series with the short switch (R
I
), and the resistance of the external source (R
S
). The
sampling capacitor C
S
should be greater than 100 pF. The time constant, Tau, to charge the sampling
capacitor C
S
can be calculated with the following equation:
Tau = (R
I
+ R
S
) × C
S
Depending on the required accuracy, 3 to 10 Tau should be used as a sampling time. With 3 Tau, the
sampling capacitor is charged to approximately 95% of the input signal's voltage level; with 5 Tau, it is
charged to more than 99%; and with 10 Tau, the sampled voltage is sufficient for 12-bit accuracy.
35.2.5 Output Filter
The output of the comparator can be used with or without internal filtering. When control bit CEF is set, the
output is filtered with an on-chip RC filter. The delay of the filter can be adjusted in four steps with the
CEFDLY bit.
All comparator outputs oscillate if the voltage difference across the input terminals is small (see
). Internal and external parasitic effects and cross coupling on and between signal lines, power supply
lines, and other parts of the system are responsible for this behavior. The comparator output oscillation
reduces the accuracy and resolution of the comparison result. Enable the output filter to reduce errors
associated with comparator oscillation.