TLC1550I Datasheet, PDF (7/9 Pages) Texas Instruments – 10-BIT ANALOG-TO-DIGITAL CONVERTERS WITH PARALLEL OUTPUTS

TLC1550I, TLC1550M, TLC1551I
10-BIT ANALOG-TO-DIGITAL CONVERTERS
WITH PARALLEL OUTPUTS
SLAS043C – MAY 1991 – REVISED MARCH 1995
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:
+ ǒ ń Ǔ The capacitance charging voltage is given by
VC VS 1– e– ^{tc RtCi}
(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)
* ǒ ń Ǔ + ǒ ń Ǔ Equating equation 1 to equation 2 and solving for time tc gives
VS VS 512 VS 1– e– ^{tc RtCi}
(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
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
2–7