0000
1100
1101
1110
1111
0000
0001
0010
0011
1100
1101
1110
1111
CESHORT
Sampling capacitor, C
S
Analog Inputs
COMP_E Operation
890
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Comparator E Module (COMP_E)
Figure 23-2. COMP_E Sample-And-Hold
The required sampling time is proportional to the size of the sampling capacitor (C
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
Tau = (R
I
+ R
S
) × C
S
(12)
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 signals 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.
23.2.5 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 different steps.
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. Selecting the output filter can reduce errors
associated with comparator oscillation.