REV. 0

AD9845A

–21–

Internal Power-On Reset Circuitry

After power-on, the AD9845A will automatically reset all inter-

nal 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. Pin 43 (formerly RSTB on the AD984x non-A

products) is no longer used for the reset operation. Toggling Pin

43 in the AD9845A will have no effect.

Grounding and Decoupling Recommendations

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

for the AD9845A. 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 AD9845A, 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, reducing digital power

dissipation, and reducing potential noise coupling. If the digital

outputs (Pins 3–12) must drive a load larger than 20 pF, buffer-

ing is recommended to reduce digital code transition noise.

Alternatively, placing series resistors close to the digital out-

put pins may also help reduce noise.

36

35

34

33

32

31

30

29

28

27

26

25

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

1

2

3

4

5

6

7

8

9

10

11

12

37

48 47 46 45 44

39 38

43 42 41 40

PIN 1

IDENTIFIER

TOP VIEW

(Not to Scale)

AUX1IN

AVSS

AUX2IN

AVDD2

BYP4

NC

CCDIN

BYP2

BYP1

AVDD1

AVSS

AVSS

D0

D1

D2

D3

D4

D5

D6

D7

D8

(MSB) D11

AD9845A

0.1 F

0.1 F

0.1 F

0.1 F

0.1 F

0.1 F

3V

ANALOG SUPPLY

CCD SIGNAL

3V

ANALOG SUPPLY

12

DATA

OUTPUTS

3

SERIAL

INTERFACE

0.1 F

1.0 F

1.0 F

0.1 F

3V

ANALOG SUPPLY

8

CLOCK

INPUTS

0.1 F

0.1 F

3V

ANALOG SUPPLY

3V

DRIVER

SUPPLY

NC = NO CONNECT

D9

D10

Figure 33. Recommended Circuit Configuration for CCD-Mode