MAX1460 Просмотр технического описания (PDF) - Maxim Integrated

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MAX1460

Low-Power, 16-Bit Smart ADC

Maxim Integrated 

MAX1460

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 Off-

set DAC, ADC, and Temperature Sensor

Before the sensor signal is digitized, it must be gained

and coarse-offset corrected to maximize the ADC dynam-

ic 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 analog

–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

RESISTOR BETWEEN THE

TOP OF THE BRIDGE

AND VDD , THEN

START OVER.

VDD

SERIES

RESISTOR

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

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