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零件编号 | ZN428 | ||
描述 | 8-BIT LATCHED INPUT D-A CONVERTER | ||
制造商 | ETC | ||
LOGO | |||
1 Page
THIS DOCUMENT IS FOR MAINTENANCE
PURPOSES ONLY AND IS NOT
RECOMMENDED FOR NEW DESIGNS
UNIPOLAR ADJUSTMENT PROCEDURE
(i) Set all bits to OFF (low) with ENABLE low and adjust
zero until VOUT = 0.0000V.
(ii) Set all bits ON (high) and adjust gain until VOUT = FS
- 1LSB.
UNIPOLAR SETTING UP POINTS
Output Range, +FS
LSB
FS - 1LSB
+5V
19.5 mV
4.9805V
+10V
39.1mV
9.9609V
1LSB = FS
256
ZN428
UNIPOLAR LOGIC CODING
Input Code
(Binary)
11111111
11111110
11000000
10000001
10000000
01111111
01000000
00000001
00000000
Analog Output
(Nominal Value)
FS - 1LSB
FS - 2 LSB
3/4 FS
1/2 FS + 1LSB
1/2 FS
1/2 FS - 1LSB
1/4 FS
1LSB
0
Fig.9 Bipolar operation - basic circuit
(2) Bipolar D-A Converter
For bipolar operation the output from the ZN428 is offset
by half full-scale by connecting a resistor R3 between VREF
IN and the inverting input of the buffer amplifier (Fig.9).
When the digital input to the ZN428 is zero the analog
output is zero and the amplifier output should be -Full-scale.
An input of all ones to the D-A will give a ZN428 output of
VREF IN and the amplifier output required is +Full-scale. Also,
to match the ladder resistance the parallel combination of
R1, R2 and R3 should be 4kΩ.
The nominal values of R1, R2 and R3 which meet these
conditions are given by
R1 = 8GkΩ, R2 = 8G/(G-1)kΩ and R3 = 8kΩ.
where the resultant output range is ±G VREF IN. A bipolar
output range of ±VREF IN (which corresponds to the basic
unipolar range 0 to VREF IN) is obtained if R1 = R3 = 8kΩ and
R2 = ∞.
Assuming that VREF IN = 2.5V the nominal values of
resistors for ±5 and ±10V output ranges are given in the
following table:
Output Range G
+5V 2
+10V
4
R1
16kΩ
32kΩ
R2
16kΩ
10.66kΩ
R3
8kΩ
8kΩ
Minus full scale (0ffset) is set by adjusting R1 about its
nominal value relative to R3. Plus full-scale (gain) is set by
adjusting R2 relative to R1.
Practical circuit realisations are given in Fig.10.
Note that in the ±5V case R3 has been chosen as 7.5kΩ
(instead of 8.2kΩ) to get a more symmetrical range of
adjustment using standard potentiometers. Settling time for a
major transition is 1.5µs typical.
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页数 | 9 页 | ||
下载 | [ ZN428.PDF 数据手册 ] |
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