AD9824 datasheet(21/24 Pages) AD

21 / 24 page

REV. 0

AD9824

–21–

Internal Power-On Reset Circuitry

After power-on, the AD9824 will automatically reset all internal

registers and perform internal calibration procedures. This takes

approximately 1 ms to complete. During this time, normal

clock signals and serial write operations may occur. However,

serial register writes will be ignored until the internal reset opera-

tion is completed.

Grounding and Decoupling Recommendations

As shown in Figure 33, a single ground plane is recommended

for the AD9824. This ground plane should be as continuous as

possible, particularly around Pins 25 through 39. This will

ensure that all analog decoupling capacitors provide the lowest

possible impedance path between the power and bypass pins and

their respective ground pins. All decoupling capacitors should

be located as close as possible to the package pins. A single clean

power supply is recommended for the AD9824, but a separate

digital driver supply may be used for DRVDD (Pin 13). DRVDD

should always be decoupled to DRVSS (Pin 14), which should

be connected to the analog ground plane. Advantages of using

a separate digital driver supply include using a lower voltage

(2.7 V) to match levels with a 2.7 V ASIC, and reducing digital

power dissipation and potential noise coupling. If the digital

outputs (Pins 1–12) must drive a load larger than 20 pF, buff-

ering is recommended to reduce digital code transition noise.

Alternatively, placing series resistors close to the digital out-

put pins may also help reduce noise.

13 14 15 16 17 18 19 20 21 22 23 24

48 47 46 45 44

39 38

43 42 41 40

PIN 1

IDENTIFIER

TOP VIEW

(Not to Scale)

AUX1IN

AVSS

AUX2IN

AVDD2

BYP3

CCDIN

BYP2

BYP1

AVDD1

AVSS

D10

(MSB) D13

AD9824

0.1 F

ANALOG SUPPLY

CCD SIGNAL

ANALOG SUPPLY

DATA

OUTPUTS

SERIAL

INTERFACE

1.0 F

0.1 F

ANALOG SUPPLY

CLOCK

INPUTS

0.1 F

ANALOG SUPPLY

DRIVER

SUPPLY

NC = NO CONNECT

D11

D12

Figure 33. Recommended Circuit Configuration for CCD-Mode

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