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ADC081000 View Datasheet(PDF) - National ->Texas Instruments

Part NameDescriptionManufacturer
ADC081000 High Performance, Low Power 8-Bit, 1 GSPS A/D Converter National-Semiconductor
National ->Texas Instruments National-Semiconductor
ADC081000 Datasheet PDF : 30 Pages
First Prev 21 22 23 24 25 26 27 28 29 30
To help ease data capture, the output data may be caused to
transition on either the positive or the negative edge of the
output data clock (DCLK). This is chosen with the OutEdge
input. A high on the OutEdge input causes the output data to
transition on the rising edge of DCLK, while grounding this
input causes the output to transition on the falling edge of
DCLK.
1.5 The LVDS Outputs
The data outputs, the Out Of Range (OR) and DCLK are
LVDS compliant outputs. Output current sources provide 3
mA of output current to a differential 100 Ohm load when the
OutV input is high or 2.2 mA when the OutV input is low. For
short LVDS lines and low noise systems, satisfactory perfor-
mance may be realized with the OutV input low, which results
in lower power consumption. If the LVDS lines are long and/
or the system in which the ADC081000 is used is noisy, it may
be necessary to tie the OutV pin high.
Note that the LVDS levels are not intended to meet any given
LVDS specification, but output levels are such that interfacing
with LVDS receivers is practical.
1.6 Out Of Range (OR) Indication
The input signal is out of range whenever the correct code
would be above positive full-scale or below negative full scale.
When the input signal for any given sample is thus out of
range, the OR output is high for that word time.
1.7 Power Down
The ADC081000 is in the active state when the Power Down
pin (PD) is low. When the PD pin is high, the device is in the
power down mode, where the device power consumption is
reduced to a minimal level and the outputs are in a high
impedance state. 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 se-
quence 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.
1.8 Summary of Control Pins and Convenience Outputs
Table 1 and Table 2 are provided as a guide to the use of the
various control and convenience pins of the ADC081000.
Note that this table is only a guide and that the rest of this data
sheet should be consulted for the full meaning and use of
these pins.
TABLE 1. Digital Control Pins
PIN DESCRIPTION
LOW
HIGH
3
OutV
440mV Outputs 600mV Outputs
4
OutEdge
Data Transition Data Transition
at DCLK Fall at DCLK Rise
14
DC_Coup
A.C. Coupled D.C. Coupled
Inputs
Inputs
26
PD
Normal
Operation
Power Down
30
CAL
Normal
Operation
Run Calibration
35
FSR
600 mVP-P Full- 800 mVP-P Full-
Scale In
Scale In
127
CalDly
224 Clock
Cycles
230 Clock
Cycles
TABLE 2. Convenience Output Pins
PIN DESCRIPTION
USE / INDICATION
7
VCMO
Common Mode Output Voltage.
31
VBG
1.25V Convenience Output.
79
OR+
Differential Out-Of-Range
80
OR−
Indication; active high.
126
CalRun
Low is normal operation. High
indicates Calibration is running.
Applications Information
2.0 THE REFERENCE VOLTAGE
The voltage reference for the ADC081000 is derived from a
1.254V bandgap reference which is made available at the
VBG output for user convenience and has an output current
capability of ±100 μA. The VBG output should be buffered if
more current than this is required of it.
The internal bandgap-derived reference voltage causes the
full-scale peak-to-peak input swing to be either 600 mV or 800
mV, as determined by the FSR pin and described in Section
1.3. There is no provision for the use of an external reference
voltage.
3.0 THE ANALOG INPUT
The analog input is a differential one to which the signal
source may be a.c. coupled or d.c. coupled. Table 3 gives the
input to output relationship with the FSR pin high. With the
FSR pin grounded, the millivolt values in Table 3 are reduced
to 75% of the values indicated.
The buffered analog inputs simplify the task of driving these
inputs and the RC pole that is generally used at sampling ADC
inputs is not required. If it is desired to use an amplifier circuit
before the ADC, use care in choosing an amplifier with ade-
quate noise and distortion performance and adequate gain at
the frequencies used for the application.
23
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