MAX525 Maxim, MAX525 Datasheet - Page 14

• Manufacturer Part Number: MAX525
• Description: Low-Power / Quad / 12-Bit Voltage-Output DAC with Serial Interface
• Manufacturer: Maxim

Low-Power, Quad, 12-Bit Voltage-Output DAC
with Serial Interface
Figure 10. Unipolar Rail-to-Rail Output Circuit
Figure 11. Bipolar Output Circuit
14
V
REFAB
REF_
MAX525
______________________________________________________________________________________
DAC
= V
REFCD
REFAB
= 2.5V
MAX525
REFERENCE INPUTS
DAC A
DAC B
DAC C
DAC D
R1
REFCD
AGND
OUT_
FB_
R1 = R2 = 10k ± 0.1%
V
DD
+5V
DGND
+5V
-5V
R2
FBA
FBB
FBC
FBD
OUTA
OUTB
OUTC
OUTD
10k
10k
10k
10k
10k
10k
10k
10k
V
OUT
In applications where the reference has AC signal com-
ponents, the MAX525 has multiplying capability within
the reference input range specifications. Figure 12
shows a technique for applying a sine-wave signal to
the reference input where the AC signal is offset before
being applied to REFAB/REFCD. The reference voltage
must never be more negative than DGND.
The MAX525’s total harmonic distortion plus noise (THD
+ N) is typically less than -72dB, given a 1Vp-p signal
swing and input frequencies up to 25kHz. The typical
-3dB frequency is 650kHz, as shown in the Typical
Operating Characteristics graphs.
The circuit of Figure 13 places an NPN transistor
(2N3904 or similar) within the op-amp feedback loop to
implement a digitally programmable, unidirectional cur-
rent source. This circuit can be used to drive 4mA to
20mA current loops, which are commonly used in
industrial-control applications. The output current is cal-
culated 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 13.
Figure 12. AC Reference Input Circuit
REFERENCE
500mVp-p
INPUT
+5V
AC
Digitally Programmable Current Source
26k
I
OUT
10k
= (V
REF
Using an AC Reference
DAC_
/ R) x (NB / 4096)
1/2 MAX492
REF_
AGND
MAX525
V
DD
DGND
OUT_