TLC1550I_15 Datasheet, PDF (8/18 Pages) Texas Instruments – 10-BIT ANALOG-TO-DIGITAL CONVERTERS WITH PARALLEL OUTPUTS

TLC1550I, TLC1550M, TLC1551I
10ĆBIT ANALOGĆTOĆDIGITAL CONVERTERS
WITH PARALLEL OUTPUTS
SLAS043G − MAY 1991 − REVISED NOVEMBER 2003
APPLICATION INFORMATION
simplified analog input analysis
Using the circuit in Figure 2, the time required to charge the analog input capacitance from 0 to V_S within 1/2
LSB can be derived as follows:
The capacitance charging voltage is given by
ǒ Ǔ VC + VS 1−e–tc^ńRtCi
(1)
Where:
R_t = R_s + r_i
The final voltage to 1/2 LSB is given by
V_C (1/2 LSB) = V_S − (V_S /1024)
(2)
Equating equation 1 to equation 2 and solving for time t_c gives
ǒ Ǔ ǒ Ǔ VS * VSń512 + VS 1–e–tc^ńRtCi
(3)
and
t _c (1/2 LSB) = R_t × C_i × ln(1024)
(4)
Therefore, with the values given, the time for the analog input signal to settle is
t _c (1/2 LSB) = (R_s + 1 kΩ) × 60 pF × ln(1024)
(5)
This time must be less than the converter sample time shown in the timing diagrams.
Driving Source†
TLC1550/1
Rs
VI
ri
VS
VC
1 kΩ MAX
Ci
50 pF MAX
VI = Input voltage at AIN
VS = External driving source voltage
Rs = Source resistance
ri = Input resistance
Ci = Input capacitance
† _{Driving source requirements:}
• Noise and distortion for the source must be equivalent to the resolution of the converter.
• Rs must be real at the input frequency.
Figure 2. Input Circuit Including the Driving Source
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