ADC08D502 Datasheet, PDF (39/43 Pages) Texas Instruments – ADC08D502 High Performance, Low Power, Dual 8-Bit, 500 MSPS A/D Converter

ADC08D502
www.ti.com
SNOSC85 – AUGUST 2012
USING THE SERIAL INTERFACE
The ADC08D502 may be operated in the non-extended control (non-Serial Interface) mode or in the extended
control mode. Table 14 and Table 15 describe the functions of pins 3, 4, 14 and 127 in the non-extended control
mode and the extended control mode, respectively.
Non-Extended Control Mode Operation
Non-extended control mode operation means that the Serial Interface is not active and all controllable functions
are controlled with various pin settings. That is, the full-scale range, single-ended or differential input and input
coupling (a.c. or d.c.) are all controlled with pin settings. The non-extended control mode is used by setting pin
14 high or low, as opposed to letting it float. Table 14 indicates the pin functions of the ADC08D502 in the non-
extended control mode.
Table 14. Non-Extended Control Mode Operation
(Pin 14 High or Low)
Pin
Low
High
Floating
3
0.51 V_P-P Output
0.71 V_P-P Output
n/a
4
OutEdge = Neg
OutEdge = Pos
DDR
127
CalDly Low
CalDly High
n/a
14
650 mV_P-P input range
870 mV_P-P input range
Extended Control Mode
Pin 3 can be either high or low in the non-extended control mode. Pin 14 must not be left floating to select this
mode.
Pin 4 can be high or low or can be left floating in the non-extended control mode. In the non-extended control
mode, pin 4 high or low defines the edge at which the output data transitions. If this pin is floating, the output
clock (DCLK) is a DDR (Double Data Rate) clock and the output edge synchronization is irrelevant since data is
clocked out on both DCLK edges.
Pin 127, if it is high or low in the non-extended control mode, sets the calibration delay.
Table 15. Extended Control Mode Operation
(Pin 14 Floating)
Pin
Function
3
SCLK (Serial Clock)
4
SDATA (Serial Data)
127
SCS (Serial Interface Chip Select)
COMMON APPLICATION PITFALLS
Failure to write all register locations when using extended control mode. When using the serial interface, all
8 user registers must be written at least once with the default or desired values before calibration and
subsequent use of the ADC. In addition, the first write to register (Dh) must load the default value (0x3FFFh).
Once all registers have been written once, other desired settings can be loaded.
Driving the inputs (analog or digital) beyond the power supply rails. For device reliability, no input should
not go more than 150 mV below the ground pins or 150 mV above the supply pins. Exceeding these limits on
even a transient basis may not only cause faulty or erratic operation, but may impair device reliability. It is not
uncommon for high speed digital circuits to exhibit undershoot that goes more than a volt below ground.
Controlling the impedance of high speed lines and terminating these lines in their characteristic impedance
should control overshoot.
Care should be taken not to overdrive the inputs of the ADC08D502. Such practice may lead to conversion
inaccuracies and even to device damage.
Incorrect analog input common mode voltage in the d.c. coupled mode. The Input common mode voltage
must remain within 50 mV of the V_CMO output, which has a variability with temperature that must also be tracked.
Distortion performance will be degraded if the input common mode voltage is more than 50 mV from V_CMO .
Copyright © 2012, Texas Instruments Incorporated
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