MX7837 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MX7837 Datasheet PDF : 12 Pages
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Complete, Dual, 12-Bit
Multiplying DACs
Bipolar Operation (4-Quadrant
Multiplication)
Figure 7 shows the MX7837/MX7847 connected for
binary operation. The offset-binary coding is shown in
Table 4. When VIN is an AC signal, the circuit performs
4-quadrant multiplication. R1, R2, and R3 resistors
should be 0.01% ratio matched to maintain gain-error
specifications. On the MX7847, the RFB feedback
resistor is internally connected to VOUT.
Table 4. Bipolar Code Table
DAC Latch Contents
MSB
LSB
Analog Output, VOUT
1111 1111 1111
+VIN
×
2047
2048
1000 0000 0001
+VIN
×
1
2048
1000 0000 0000
0V
0111 1111 1111
0000 0000 0000
−VIN
×
1
2048
−VIN
×
2048
2048
= − VIN
Note :
1LSB
=
VIN
2048
__________Applications Information
Ground Management
The use of an uninterrupted ground plane is strongly
recommended. AC or transient voltages between ana-
log and digital grounds (between AGNDA/AGNDB and
DGND) can inject noise into the analog circuitry.
Connect the MX7837/MX7847 AGNDs and DGND
directly to the ground plane or to a star ground to
ensure that they are at the same potential. In complex
systems with separate analog and digital ground
planes, connect two diodes (1N914 or equivalent) in
inverse parallel between the AGND and DGND pins.
Power-Supply Decoupling
To minimize noise, decouple the VDD and VSS lines to
DGND using a 10µF capacitor in parallel with a 0.1µF
ceramic capacitor. Minimize capacitor lead lengths for
best noise rejection.
Operation with Reduced
Power-Supply Voltages
The MX7837/MX7847 are specified for operation with
VDD/VSS = ±11.4V to ±16.5V. However, the output
amplifier requires 2.5V of headroom, so the reference
input should not come within 2.5V of VDD/VSS in order to
maintain accuracy at full scale.
VDD
VDD
RFBA*
VIN
VREFA
DAC A
DGND AGNDA VSS
VOUTA*
VOUT
MX7837
VSS MX7847
VSS
* INTERNALLY CONNECTED ON MX7847
Figure 6. Unipolar Binary Operation
VDD
VDD
VIN
VREFA
DAC A
R1
20k
R3
10k
RFBA*
VOUTA
R2
20k
VOUT
MAX427
DGND AGNDA
MX7837
MX7847 VSS
VSS
* INTERNALLY CONNECTED
ON MX7847
Figure 7. Bipolar Offset Binary Operation
8 _______________________________________________________________________________________
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