TLC2551 Datasheet, PDF (18/23 Pages) Texas Instruments – 5 V, LOW POWER, 12-BIT, 400 KSPS, SERIAL ANALOG-TO-DIGITAL CONVERTERS WITH AUTOPOWER DOWN

TLC2551, TLC2552, TLC2555
5 V, LOW POWER, 12-BIT, 400 KSPS,
SERIAL ANALOG-TO-DIGITAL CONVERTERS WITH AUTOPOWER DOWN
SLAS276 –MARCH 2000
APPLICATION INFORMATION
VDD
TMS320 DSP
XF
RXD
SCLK
10 kΩ
10 kΩ
VDD
FS
SDO
VREF
SCLK
TLC2551
CS
GND
EXT
Reference
Ain
VDD
TMS320 DSP
XF
RXD
SCLK
10 kΩ
10 kΩ
VDD
CS/FSD _VREF
SDO
SCLK
TLC2552/55
† _{For TLC2555 only}
GND
Figure 22. Typical Interface to a TMS320 DSP
EXT
Reference
AIN 0/AIN (+)†
AIN 1/AIN (–)†
simplified analog input analysis
Using the equivalent circuit in Figure 23, the time required to charge the analog input capacitance from 0 to Vs
within 1/2 LSB can be derived as follows.
+ ǒ ǒ ǓǓ ^{The capacitance charging voltage is given by:}
Vc
Vs
1–EXP
–tch
Rt Ci
(1)
Where:
Rt = Rs + Zi
tch = Charge time
The input impedance Zi is 0.5 kΩ at 5 V, and is higher (~ 0.6 kΩ) at 2.7 V. The final voltage to 1/2 LSB is given
by:
ń + ^{ǒ Ǔ} Vc (1 2 LSB)
Vs–
Vs
8192
(2)
18
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