Datasheet

MAX11359A
16-Bit Data-Acquisition System with ADC, DAC,
UPIOs, RTC, Voltage Monitors, and Temp Sensor
59
Maxim Integrated
Power Supplies
AVDD and DVDD provide power to the MAX11359A. The
AV
DD
powers up the analog section, while the DVDD pow-
ers up the digital section. The power supply for both AVDD
and DVDD ranges from +1.8V to +3.6V. Both AVDD and
DVDD must be greater than +1.8V for device operation.
AVDD and DVDD can connect to the same power supply.
Bypass AVDD to AGND with a 10µF electrolytic capacitor
in parallel with a 0.1µF ceramic capacitor, and bypass
DVDD to DGND with a 10µF electrolytic capacitor in paral-
lel with a 0.1µF ceramic capacitor. For improved perfor-
mance, place the bypass capacitors as close to the device
as possible.
ADC Transfer Functions
Figures 20 and 21 provide the ADC transfer functions
for unipolar and bipolar mode. The digital output code
format is binary for unipolar mode and two’s comple-
ment for bipolar mode. Calculate 1 LSB using the fol-
lowing equations:
1 LSB (Unipolar Mode) = V
REF
/(Gain x 65,536)
1 LSB (Bipolar Mode) = ±2V
REF
/(Gain x 65,536)
where V
REF
equals the reference voltage at REF and
Gain equals the PGA gain.
In unipolar mode, the output code ranges from 0 to
65,535 for inputs from zero to full-scale. In bipolar
mode, the output code ranges from -32,768 to +32,767
for inputs from negative full-scale to positive full-scale.
DAC Unipolar Output
For a unipolar output, the output voltages and the refer-
ence have the same polarity. Figure 22 shows the
unipolar output circuit of the MAX11359A, which is also
the typical operating circuit for the DAC. Table 22 lists
some unipolar input codes and their corresponding
output voltages.
For larger output swing, see Figure 23. This circuit
shows the output amplifiers configured with a closed-
loop gain of +2V/V to provide 0 to 2.5V full-scale range
with the 1.25V reference.
DAC Bipolar Output
The MAX11359A DAC output can be configured for
bipolar operation using the application circuit in
Figure 24:
where N is the decimal value of the DAC’s binary input code.
Table 23 shows digital codes (offset binary) and corre-
sponding output voltages for Figure 24 assuming
R
1
= R
2
.
VV
N
OUT REF
=
⎛
⎝
⎜
⎞
⎠
⎟
−
⎡
⎣
⎢
⎤
⎦
⎥
2
1024
1
MAX11359A
DAC A
OUTA
V
REF
= 1.25V
FBA
10kΩ
10kΩ
R
2
R
2
= R
1
R
1
MAX11359A
DAC_
OUT_
V
OUT
+3.3V
-3.3V
FB_
V
REF
= 1.25V
V
REF
Figure 24. DAC Bipolar Output Circuit
Figure 23. DAC Unipolar Rail-to-Rail Output Circuit
DAC CONTENTS
MSB LSB
ANALOG OUTPUT
1111 1111 11 +V
REF
(1023/1024)
1000 0000 01 +V
REF
(513/1024)
1000 0000 00 +V
REF
(512/1024) = +V
REF
/2
0111 1111 11 +V
REF
(511/1024)
0000 0000 01 +V
REF
(1/1024)
0000 0000 00 0
Table 22. Unipolar Code
DAC CONTENTS
MSB LSB
ANALOG OUTPUT
1111 1111 11 +V
REF
(511/512)
1000 0000 01 +V
REF
(1/512)
1000 0000 00 0
0111 1111 11 -V
REF
(1/512)
0000 0000 01 -V
REF
(511/512)
0000 0000 00 -V
REF
(512/512) = -V
REF
Table 23. Bipolar Code