ADC08DL502
SNAS582B –MARCH 2012–REVISED MARCH 2013
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The minimum tCAL_L and tCAL_H input clock cycle sequence is required to ensure that random noise does not
cause a calibration to begin when it is not desired. As mentioned for best performance, a calibration should be
performed 20 seconds or more after power up and repeated when the operating temperature changes
significantly relative to the specific system design performance requirements.
By default, On-Command calibration also includes calibrating the input termination resistance and the ADC.
However, since the input termination resistance, once trimmed at power-up, changes marginally with
temperature, the user has the option to disable the input termination resistor trim, which will ensure that the
DCLK is continuously present at the output during subsequent calibration. The Resistor Trim Disable can be
programmed in register (address: 1h, bit 13) when in the Extended Control mode.
Calibration Delay
The CalDly input (pin 141) is used to select one of two delay times after the application of power to the start of
calibration, as described in Calibration. The calibration delay values allow the power supply to come up and
stabilize before calibration takes place. With no delay or insufficient delay, calibration would begin before the
power supply is stabilized at its operating value and result in non-optimal calibration coefficients. If the PD pin is
high upon power-up, the calibration delay counter will be disabled until the PD pin is brought low. Therefore,
holding the PD pin high during power up will further delay the start of the power-up calibration cycle. The best
setting of the CalDly pin depends upon the power-on settling time of the power supply.
Note that the calibration delay selection is not possible in the Extended Control mode and the short delay time is
used.
Output Edge Synchronization
DCLK signals are available to help latch the converter output data into external circuitry. The output data can be
synchronized with either edge of these DCLK signals. That is, the output data transition can be set to occur with
either the rising edge or the falling edge of the DCLK signal, so that either edge of that DCLK signal can be used
to latch the output data into the receiving circuit.
When OutEdge (pin 6) is high, the output data is synchronized with (changes with) the rising edge of the DCLK+
(pin 92). When OutEdge is low, the output data is synchronized with the falling edge of DCLK+.
At the very high speeds of which the ADC08DL502 is capable, slight differences in the lengths of the DCLK and
data lines can mean the difference between successful and erroneous data capture. The OutEdge pin is used to
capture data on the DCLK edge that best suits the application circuit and layout.
Reliable data capture can be achieved by using just one DCLK+/- signal for the full 32 signal data bus. However,
if desired, the user may configure the OR+/- output as the second DCLK+/- output instead.
LVDS Output Level Control
The output level can be set to one of two levels with OutV (pin 5). The strength of the output drivers is greater
with OutV high. With OutV low there is less power consumption in the output drivers, but the lower output level
means decreased noise immunity.
For short LVDS lines and low noise systems, satisfactory performance may be realized with the OutV input low.
If the LVDS lines are long and/or the system in which the ADC08DL502 is used is noisy, it may be necessary to
tie the OutV pin high.
Power Down Feature
The Power Down pins (PD and PDQ) allow the ADC08DL502 to be entirely powered down (PD) or the "Q"
channel to be powered down and the "I" channel to remain active. See Power Down for details on the power
down feature.
The digital data (+/-) output pins are put into a high impedance state when the PD pin for the respective channel
is high. Upon return to normal operation, the pipeline will contain meaningless information and must be flushed.
If the PD input is brought high while a calibration is running, the device will not go into power down until the
calibration sequence is complete. However, if power is applied and PD is already high, the device will not begin
the calibration sequence until the PD input goes low. If a manual calibration is requested while the device is
powered down, the calibration will not begin at all. That is, the manual calibration input is completely ignored in
the power down state.
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