Datasheet
AD5821A
Rev. 0 | Page 12 of 16
PD X D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X
00
SCL
SDA
START BY
MASTER
ACK BY
AD5821A
1191
ACK BY
AD5821A
ACK BY
AD5821A
STOP BY
MASTER
FRAME 3
LEAST SIGNIFICANT
DATA BYTE
FRAME 2
MOST SIGNIFICANT
DATA BYTE
FRAME 1
SERIAL BUS
ADDRESS BYTE
01 1XXR/W
9
07796-017
Figure 22. Write Operation
PD X D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X
00
SCL
SDA
1191
01 1XXR/W
START BY
MASTER
ACK BY
AD5821A
9
ACK BY
AD5821A
ACK BY
AD5821A
STOP BY
MASTER
FRAME 3
LEAST SIGNIFICANT
DATA BYTE
FRAME 2
MOST SIGNIFICANT
DATA BYTE
FRAME 1
SERIAL BUS
ADDRESS BYTE
07796-018
Figure 23. Read Operation
Table 6. Data Format
Serial Data-
Words
High Byte Low Byte
Bit
15
Bit
14
Bit
13
Bit
12
Bit
11
Bit
10
Bit
9
Bit
8
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
Serial Data
Bits
SD7 SD6 SD5 SD4 SD3 SD2 SD1 SD0 SD7 SD6 SD5 SD4 SD3 SD2 SD1 SD0
Input
Register
R15 R14 R13 R12 R11 R10 R9 R8 R7 R6 R5 R4 R3 R2 R1 R0
Function XSHUTDOWN
1
X D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X
1
XSHUTDOWN = soft power-down; X = unused/don’t care; and D9 to D0 = AC data.
POWER SUPPLY BYPASSING AND GROUNDING
When accuracy is important in an application, it is beneficial
to consider power supply and ground return layout on the PCB.
The PCB for the AD5821A should have separate analog and digital
power supply sections. Where shared AGND and DGND is
necessary, the connection of grounds should be made at only
one point, as close as possible to the AD5821A.
V
BATTERY
Pay special attention to the layout of the AGND return path and,
and trace it between the voice coil motor and I
SINK
to minimize
any series resistance. Figure 24 shows the output current sink
of the AD5821A and illustrates the importance of reducing the
effective series impedance of AGND and the trace resistance
between the motor and I
SINK
. The voice coil is modeled using
Inductor L
C
and Resistor R
C
. The current through the voice coil
is effectively a dc current that results in a voltage drop, V
COIL
,
when the AD5821A is sinking current. The effect of any series
inductance is minimal.
AGND
AD5821A
Q1
GROUND
RETURN
I
SINK
V
DROP
R
SENSE
R
R
G
L
G
V
COIL
R
T
R
C
L
C
TRACE
RESISTANCE
VOICE
COIL
SDA
SCL
SHUTDOWN
DGND
DGND
V
DD
X
07796-019
Figure 24. Effect of PCB Trace Resistance and Inductance