EVAL-AD5398EB【PDF 11/16 页】120 mA, Current Sinking, 10-Bit, I2C DAC

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Sheet目录362800

7页 8页 9页 10页 [11页]12页 13页 14页 15页

AD5398

Rev. A | Page 11 of 16

SCL

SDA

START BY

MASTER

ACK BY

AD5398

ACK BY

AD5398

ACK BY

AD5398

STOP BY

MASTER

FRAME 3

LEAST SIGNIFICANT

DATA BYTE

FRAME 2

MOST SIGNIFICANT

DATA BYTE

FRAME 1

SERIAL BUS

ADDRESS BYTE

R/W

Figure 17. Write Operation

SCL

SDA

START BY

MASTER

ACK BY

AD5398

ACK BY

AD5398

ACK BY

AD5398

STOP BY

MASTER

FRAME 3

LEAST SIGNIFICANT

DATA BYTE

FRAME 2

MOST SIGNIFICANT

DATA BYTE

FRAME 1

SERIAL BUS

ADDRESS BYTE

R/W

Figure 18. Read Operation

Table 6. Data Format

Serial Data-Words

Serial Data Bits

Input Register

Function

PD = soft power-down; X = unused/don’t care; D9 to D0 = DAC 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 AD5398 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 AD5398.

High Byte

SD7

R15

Low Byte

SD7

SD6

R14

SD5

R13

SD4

R12

SD3

R11

SD2

R10

SD1

SD0

SD6

SD5

SD4

SD3

SD2

SD1

SD0

Special attention should be paid to the layout of the AGND

return path and track between the voice coil motor and I

SINK

minimize any series resistance. Figure 19 shows the output

current sink of the AD5398 and illustrates the importance of

reducing the effective series impedance of AGND, and the track

resistance between the motor and I

SINK

. The voice coil is

modeled as inductor L

and resistor R

. The current through

the voice coil is effectively a dc current that results in a voltage

drop, V

, when the AD5398 is sinking current; the effect of any

series inductance is minimal. The maximum voltage drop

allowed across R

SENSE

is 400 mV, and the minimum drain to

source voltage of Q1 is 200 mV. This means that the AD5398

output has a compliance voltage of 600 mV. If V

DROP

falls below

600 mV, the output transistor, Q1, can no longer operate

properly and I

SINK

might not be maintained as a constant.

AGND

GROUND

RESISTANCE

GROUND

INDUCTANCE

SINK

SENSE

DROP

BAT

TRACE

RESISTANCE

VOICE

COIL

ACTUATOR

Figure 19. Effect of PCB Trace Resistance and Inductance

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