AD7762 datasheet(17/28 Pages) AD

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AD7762

Rev. 0 | Page 17 of 28

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

CPB1/2

Normal

51 pF

12 pF

20 pF

Low Power

13 pF

12 pF

5 pF

USING THE AD7762

The following is the recommended sequence for powering up

and using the AD7762.

Apply power.

Start the clock oscillator, applying MCLK.

Take RESET low for a minimum of 1 MCLK cycle.

Wait a minimum of 2 MCLK cycles after RESET has been

released.

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.

Write to Control Register 1 to set the output data rate.

Wait a minimum of 5 MCLK cycles after CS has been

released.

Take SYNC low for a minimum of 4 MCLK cycles, if

required, to synchronize multiple parts.

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.

AD7762 Datasheet(PDF) 17 Page - Analog Devices

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