MAX1415 Datasheet, PDF (32/36 Pages) Maxim Integrated Products – 16-Bit, Low-Power, 2-Channel, Sigma-Delta ADCs

16-Bit, Low-Power, 2-Channel,
Sigma-Delta ADCs
Applications Information
Applications Examples
Strain-Gauge Measurement
Connect the differential inputs of the MAX1415/
MAX1416 to the bridge network of the strain gauge. In
Figure 12, the analog positive supply voltage powers the
bridge network and the MAX1415/MAX1416 along with
the reference voltage in a ratiometric configuration. The
on-chip PGA allows the MAX1415/MAX1416 to handle an
analog input voltage range as low as 20mV to full scale.
Optical Isolation
For applications that require an optically isolated inter-
face, see Figure 13. With 6N136-type optocouplers, the
maximum clock speed is 4MHz. The maximum clock
speed is limited by the degree of mismatch between
the individual optocouplers. Faster optocouplers allow
faster signaling at a higher cost.
Layout, Grounding, and Bypassing
Use PC boards with separate analog and digital
ground planes. Connect the two ground planes togeth-
er at the MAX1415/MAX1416 GND. Isolate the digital
supply from the analog with a low-value resistor (10Ω)
or ferrite bead when the analog and digital supplies
come from the same source.
Ensure that digital return currents do not pass through
the analog ground and that return-current paths are low
impedance. A 5mA current flowing through a PC board
ground trace impedance of only 0.05Ω creates an error
voltage of approximately 250µV.
Layout the PC board to ensure digital and analog signal
lines are kept separate. Do not run digital lines (especial-
ly the SCLK and DOUT) parallel to any analog lines. If
they must cross one another, do so at right angles.
Bypass V_DD to the analog ground plane with a 0.1µF
capacitor in parallel with a 1µF to 10µF low-ESR capac-
itor. Keep capacitor leads short for best supply-noise
rejection. Bypass REF+, REF-, and all analog inputs
with a 0.1µF capacitor to GND. Place all bypass capac-
itors as close to the device as possible to achieve the
best decoupling.
Definitions
Integral Nonlinearity
Integral nonlinearity (INL) is the deviation of the values
on an actual transfer function from a straight line. This
straight line is either a best-straight-line fit or a line
drawn between the endpoints of the transfer function,
once offset and gain errors have been nullified. INL for
the MAX1415/MAX1416 is measured using the end-
point method. This is the more conservative method.
V_{DD 10µF}
0.1µF
R_REF
ACTIVE
GAUGE
DUMMY
GAUGE
0.1µF
REF+
V_DD CLKIN
REF-
CLKOUT
0.1µF
MAX1415 ^CS
R
MAX1416 _SCLK
AIN1+
0.1µF
DIN
DOUT
AIN1-
0.1µF
R
DRDY
RESET
GND
Figure 12. Strain Gauge Measurement
Unipolar Offset Error
For an ideal converter, the first transition occurs at 0.5
LSB above zero. Offset error is the amount of deviation
between the measured first transition point and the
ideal point.
Bipolar Zero Error
In bipolar mode, the ideal midscale transition occurs at
AIN+ - AIN- = 0. Bipolar zero error is the measured
deviation from this ideal value.
Gain Error
With a full-scale analog input voltage applied to the
ADC (resulting in all ones in the digital code), gain error
is defined as the amount of deviation between the ideal
transfer function and the measured transfer function
(with the offset error or bipolar zero error removed).
Gain error is usually expressed in LSB or a percent of
full-scale range (%FSR).
Positive Full-Scale Error
For the ideal transfer curve, the code edge transition
that causes a full-scale transition to occur is 1.5 LSB
below full scale. The positive full-scale error is the dif-
ference between this code transition of the ideal trans-
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