MAX5501 Maxim Integrated Products, MAX5501 Datasheet - Page 13

• Manufacturer Part Number: MAX5501
• Description: (MAX5500 / MAX5501) 12-Bit Voltage-Output DACs
• Manufacturer: Maxim Integrated Products

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The circuit of Figure 12 places an npn transistor
(2N3904 or similar) within the op-amp feedback loop to
implement a digitally programmable, unidirectional cur-
rent source. This circuit drives 4mA to 20mA current
loops, which are commonly used in industrial-control
applications. The output current is calculated with the
following equation:
where NB is the numeric value of the DAC’s binary input
code and R is the sense resistor shown in Figure 12.
On power-up, all input and DAC registers are cleared
(set to zero code) and D
shifted out of DOUT on the clock’s falling edge).
Figure 11. Bipolar Output Circuit
REF_
Digitally Programmable Current Source
DAC
MAX5500
MAX5501
Voltage-Output DACs with Serial Interface
I
OUT
Power-Supply Considerations
______________________________________________________________________________________
= (V
R1
REF
OUT
/R) x (NB/4096)
OUT_
FB_
R1 = R2 = 10kΩ ± 0.1%
is in mode 0 (serial data is
+5V
-5V
R2
V
OUT
Low-Power, Quad, 12-Bit
For rated MAX5500/MAX5501 performance, limit V
V
capacitor in parallel with a 0.1µF capacitor to AGND.
Use short lead lengths and place the bypass capaci-
tors as close as possible to the supply inputs.
Digital or AC transient signals between AGND and
DGND create noise at the analog outputs. Connect
AGND and DGND together at the DAC, and then con-
nect this point to the highest-quality ground available.
Good PCB ground layout minimizes crosstalk between
DAC outputs, reference inputs, and digital inputs.
Reduce crosstalk by keeping analog lines away from
digital lines. Do not use wire-wrapped boards.
PROCESS: BiCMOS
Figure 12. Digitally Progammable Current Source
REFCD
Grounding and Layout Considerations
to 1.4V below V
REF_
DAC_
MAX5500
MAX5501
DD
. Bypass V
Chip Information
OUT_
FB_
DD
2N3904
V
with a 4.7µF
L
R
I
OUT
REFAB
13
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