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參數資料
| 型號： | AD7849TQ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | DAC |
| 英文描述： | Serial Input, 14-Bit/16-Bit DAC |
| 中文描述： | SERIAL INPUT LOADING, 7 us SETTLING TIME, 16-BIT DAC, CDIP20 |
| 封裝： | CERDIP-20 |
| 文件頁數： | 14/15頁 |
| 文件大小： | 211K |
| 代理商： | AD7849TQ |
REV. B
–
14
–
AD7849
APPLICATIONS
Opto-Isolated Interface
In many process control type applications it is necessary to
provide an isolation barrier between the controller and the unit
being controlled. Opto isolators can provide voltage isolation in
excess of 3 kV. The serial loading structure of the AD7849
makes it ideal for opto-isolated interfaces as the number of
interface lines is kept to a minimum.
Figure 25 shows a 4-channel isolated interface using the
AD7849. The DCEN pin must be connected high to enable the
daisy-chain facility. Four channels with 14-bit or 16-bit resolu-
tion are provided in the circuit shown, but this may be expanded
to accommodate any number of DAC channels without any
extra isolation circuitry. The only limitation is the output up-
date rate. For example, if an output update rate of 10 kHz is
required, then all the DACs must be loaded and updated in a
time period of 100
μ
s. Operating at the maximum clock rate of
5 MHz means that it takes 3.2
μ
s to load a DAC. This means
that the total number of channels for this update rate would be
31. This leaves 800 ns for the
LDAC
pulse. Of course, as the
update rate requirement decreases, the number of possible
channels increases.
The sequence of events to program the output channels in Fig-
ure 25 is as follows.
1. Take the
SYNC
line low.
2. Transmit the data as four 16-bit words. A total of 64 clock
pulses is required to clock the data through the chain.
3. Take the
SYNC
line high.
4. Pulse the
LDAC
line low. This updates all output channels
simultaneously on the falling edge of
LDAC
.
To reduce the number of opto-couplers, the
LDAC
line could
be driven from a one-shot which is triggered by the rising edge
on the
SYNC
line. A low level pulse of 100 ns duration or
greater is all that is required to update the outputs.
V
DD
DATA OUT
CLOCK OUT
SYNC OUT
CONTROL OUT
CONTROLLER
V
OUT
A
+5V
QUAD OPTO-COUPLER
*ADDITIONAL PINS OMITTED FOR CLARITY
V
DD
V
DD
V
DD
SCLK
SYNC
LDAC
SDIN
V
OUT
DCEN
SDOUT
AD7849*
V
OUT
B
+5V
SCLK
SYNC
LDAC
SDIN
V
OUT
DCEN
SDOUT
AD7849*
V
OUT
C
+5V
SCLK
SYNC
LDAC
SDIN
V
OUT
DCEN
SDOUT
AD7849*
V
OUT
D
+5V
SCLK
SYNC
LDAC
SDIN
V
OUT
DCEN
SDOUT
AD7849*
Figure 25. Four-Channel Opto-Isolated Interface
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