MAX1460 Datasheet, PDF (7/20 Pages) Maxim Integrated Products – Low-Power, 16-Bit Smart ADC

Low-Power, 16-Bit Smart ADC
ducer by applying power and the START signal. Latch
the 12-bit parallel digital output using the EOC pulse.
The maximum conversion rate of the MAX1460 is 15Hz,
using a 2MHz resonator. If an analog output is desired,
build a simple lowpass filter using the OUT pin, the
uncommitted op amp, and a few discrete components
(Figure 8).
Analog Front End, Including PGA, Coarse
Offset DAC, ADC, and Temperature Sensor
Before the sensor signal is digitized, it must be gained
and coarse-offset corrected to maximize the ADC
dynamic range. There are 2 bits (four possible settings)
in the configuration register for the PGA gain, and 3 bits
(eight possible settings) for the CO DAC. The flowchart
(Figure 1) shows a procedure for finding the optimum
–MAKE A TEST SYSTEM VARIABLE CALLED “NoMoreGain.”
–SET THE TEMPERATURE TO WHERE THE SENSOR’S SENSITIVITY IS HIGHEST. THIS IS NORMALLY COLD FOR SILICON PRTs.
–SET THE PGA GAIN SETTINGS TO MINIMUM.
–CLEAR THE VARIABLE “NoMoreGain.”
–APPLY MIDSCALE EXCITATION TO THE SENSOR.
–FIND THE COARSE OFFSET DAC SETTING WHERE THE DIGITIZED SIGNAL REGISTER IS CLOSEST TO ZERO (MIDSCALE).
–APPLY MAXIMUM SENSOR EXCITATION.
–TEST FOR CLIPPING (DIGITIZED SIGNAL > 0.85).
–APPLY MINIMUM SENSOR EXCITATION.
–TEST FOR CLIPPING (DIGITIZED SIGNAL < -0.85).
YES
DID ADC CLIP?
IS THE PGA AT
MINIMUM GAIN?
THE SENSOR SENSITIVITY
IS TOO LARGE. ADD A
V_DD
RESISTOR BETWEEN THE
TOP OF THE BRIDGE
AND V_DD , THEN
SERIES
RESISTOR
START OVER.
YES
NO
NO
SENSOR
–REDUCE THE PGA GAIN ONE STEP.
–SET THE VARIABLE “NoMoreGain.”
IS THE PGA AT
MAXIMUM GAIN?
NO
NO
IS “NoMoreGain” SET?
YES
YES
INCREASE THE PGA GAIN ONE STEP.
RECORD THE PGA AND COARSE OFFSET SETTINGS.
CAUTION: CLIPPING IS STILL POSSIBLE FOR LARGE SENSOR’S OFFSET TC AND LARGE TEMPERATURE RANGES.
IF NECESSARY, GUARDBAND AGAINST CLIPPING BY REDUCING THE ±0.85 CLIPPING CONSTANTS ABOVE.
Figure 1. Flowchart for Determining PGA and CO Settings
_______________________________________________________________________________________ 7