AD9945 Analog Devices, AD9945 Datasheet - Page 13

• Manufacturer Part Number: AD9945
• Description: Complete 12-Bit 40 MHz CCD Signal Processor
• Manufacturer: Analog Devices

Internal Power-On Reset Circuitry
After power-on, the AD9945 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 operation
is completed.
Grounding and Decoupling Recommendations
As shown in Figure 11, a single ground plane is recommended for
the AD9945. This ground plane should be as continuous as
possible. This will ensure that all analog decoupling capacitors
provide the lowest possible impedance path between the power
REV. A
OUTPUTS
DATA
NOTE
THE EXPOSED PAD ON THE BOTTOM OF THE AD9945 SHOULD BE
SOLDERED TO THE GND PLANE OF THE PRINTED CIRCUIT BOARD
12
Figure 11. Recommended Circuit Configuration for CCD Mode
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
SUPPLY
DRIVER
1
2
3
4
5
6
7
8
INTERFACE
3V
SERIAL
0.1 F
PIN 1
IDENTIFIER
(Not to Scale)
TOP VIEW
AD9945
3
0.1 F
–13–
3V
ANALOG
SUPPLY
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 AD9945,
but a separate digital driver supply may be used for DRVDD
(Pin 11). DRVDD should always be decoupled to DRVSS (Pin 12),
which should be connected to the analog ground plane. Advan-
tages 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 1 to 10, 31, and 32) must drive a
load larger than 20 pF, buffering is recommended to reduce
digital code transition noise. Alternatively, placing series resis-
tors close to the digital output pins may also help reduce noise.
24
23
22
21
20
19
18
17
NC = NO CONNECT
REFB
REFT
CCDIN
AVSS
AVDD
SHD
SHP
CLPOB
0.1 F
1.0 F
1.0 F
5
CLOCK
INPUTS
0.1 F
3V
ANALOG
SUPPLY
CCDIN
AD9945