参数资料
型号: AD7840KPZ
厂商: Analog Devices Inc
文件页数: 14/16页
文件大小: 0K
描述: IC DAC 14BIT LOW PWR 5V 28-PLCC
产品培训模块: Data Converter Fundamentals
DAC Architectures
标准包装: 1
设置时间: 2.5µs
位数: 14
数据接口: 串行,并联
转换器数目: 1
电压电源: 双 ±
功率耗散(最大): 100mW
工作温度: 0°C ~ 70°C
安装类型: 表面贴装
封装/外壳: 28-LCC(J 形引线)
供应商设备封装: 28-PLCC(11.51x11.51)
包装: 管件
输出数目和类型: 1 电压,双极
采样率(每秒): 400k
AD7840
REV. B
–7–
Table III. Parallel Mode Truth Table
CS
WR
LDAC
Function
HX
H
}Both Latches Latched
XH
H
L
H
Input Latch Transparent
HH
L
}
Input Latch Latched
H
X
L
DAC Latch Transparent
X
H
L
Analog Output Updated
ff
L
Input Latch Transparent
DAC Latch Data Transfer Inhibited
L
g
L
}Input Latch Is Latched
g
L
DAC Latch Data Transfer Occurs
X = Don’t Care
Figure 6. Parallel Mode Timing Diagram
Figure 7. AD7840 Simplified Parallel Input Control Logic
Serial Data Format
The serial data format is selected for the AD7840 by connecting
the CS/SERIAL line to –5 V. In this case, the WR/SYNC,
D13/SDATA, D12/SCLK, D11/FORMAT and D10/JUSTIFY
pins all assume their serial functions. The unused parallel inputs
should not be left unconnected to avoid noise pickup. Serial
data is loaded to the input latch under control of SCLK, SYNC
and SDATA. The AD7840 expects a 16-bit stream of serial data
on its SDATA input. Serial data must be valid on the falling
edge of SCLK. The SYNC input provides the frame synchroni-
zation signal which tells the AD7840 that valid serial data will
be available for the next 16 falling edges of SCLK. Figure 8
shows the timing diagram for serial data format.
Figure 8. Serial Mode Timing Diagram
Although 16 bits of data are clocked into the AD7840, only 14
bits go into the input latch. Therefore, two bits in the stream are
don’t cares since their value does not affect the input latch data.
The order and position in which the AD7840 accepts the 14 bits
of input data depends upon the FORMAT and JUSTIFY in-
puts. There are four different input data modes which can be
chosen (see Table I in the Pin Function Description section).
The first mode (M1) assumes that the first two bits of the input
data stream are don’t cares, the third bit is the LSB and the last
(or 16th bit) is the MSB. This mode is chosen by tying both the
FORMAT and JUSTIFY pins to a logic 0. The second mode
(M2; FORMAT = 0, JUSTIFY = 1) assumes that the first bit in
the data stream is the LSB, the fourteenth bit is the MSB and
the last two bits are don’t cares. The third mode (M3;
FORMAT= 1, JUSTIFY 0) assumes that the first two bits in
the stream are again don’t cares, the third bit is now the MSB
and the sixteenth bit is the LSB. The final mode (M4; FOR-
MAT = 1, JUSTIFY= 1) assumes that the first bit is the MSB,
the fourteenth bit is the LSB and the last two bits of the stream
are don’t cares.
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