EVAL-AD7762EB View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7762EB' PDF : 28 Pages View PDF
The sampling switches SS1 and SS3 are driven by ICLK, whereas
the sampling switches SS2 and SS4 are driven by ICLK. When
ICLK is high, the analog input voltage is connected to CS1. On
the falling edge of ICLK, the SS1 and SS3 switches open, and the
analog input is sampled on CS1. Similarly, when ICLK is low, the
analog input voltage is connected to CS2. On the rising edge of
ICLK, the SS2 and SS4 switches open, and the analog input is
sampled on CS2.
Capacitors CPA, CPB1, and CPB2 represent parasitic capacitances
that include the junction capacitances associated with the MOS
switches.
Table 9. Equivalent Component Values
Mode
CS1
CS2
CPA
Normal
51 pF
51 pF
12 pF
Low Power 13 pF
13 pF
12 pF
CPB1/2
20 pF
5 pF
USING THE AD7762
The following is the recommended sequence for powering up
and using the AD7762.
1. Apply power.
2. Start the clock oscillator, applying MCLK.
3. Take RESET low for a minimum of 1 MCLK cycle.
4. Wait a minimum of 2 MCLK cycles after RESET has been
released.
5. Write to Control Register 2 to power up the ADC and the
differential amplifier as required. The correct clock divider
(CDIV) ratio should be programmed now.
6. Write to Control Register 1 to set the output data rate.
7. Wait a minimum of 5 MCLK cycles after CS has been
released.
8. Take SYNC low for a minimum of 4 MCLK cycles, if
required, to synchronize multiple parts.
AD7762
Data can then be read from the part using the default filter,
offset, gain, and overrange threshold values. The conversion
data read is not valid, however, until the group delay of the filter
has passed. When this has occurred, the DVALID bit read with
the data LSW is set, indicating that the data is indeed valid.
The user can then download a different filter, if required
(see Downloading a User-Defined Filter). Values for gain, offset,
and overrange threshold registers can be written or read at this
stage.
BIAS RESISTOR SELECTION
The AD7762 requires a resistor to be connected between the
RBIAS pin and AGND1. The value for this resistor is dependant
on the reference voltage being applied to the device. The resistor
value should be selected to give a current of 25 μA through the
resistor to ground. For a 2.5 V reference voltage, the correct
resistor value is 100 kΩ and for a 4.096 V reference, the correct
resistor value is 160 kΩ.
Rev. 0 | Page 17 of 28
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