FS970X datasheet(29/46 Pages) FORTUNE

29 / 46 page

FS970X

Rev. 4.4

29/46

Interrupt

read SUM2<15:0>

SUM2<0>

=0 or 1

SUM2<0>=1

SUM2<0>=0

SUM2<15:0>-D

os-SUM2<15:0>

Wait for next

interrupt

Cal and Display

Graph 13. The flow-Chart of operation and display of fast ADC output.

The output frequency of fast ADC is the same as the first zero-point frequency of COMB2. When sampling

frequency

=166 kHz, if set TPS2<1:0>=11, then, the output frequency will be about 650 Hz.

11..3

Scale-type resistance measurement and Analog Bargraph

FS970X is equipped with fast ADC output SUM2. In the application of DMM, it can be used for Analog

Bargraph display.

However, as shown in Formula 6, when performing the scale-type resistor measurement, the reference voltage

of feeding ADC is no longer a constant value. Thus, the equivalent digital value

of the offset voltage is no

longer a constant value, either. It varies with resistor. The method of deduction of

when performing the

calculation, as described in Section 8.5.2, is no longer adequate.

As shown in Graph 14, the reference voltage below 5 M varies between the range of 0.8 V~1.2 V. According

to Formula 4, the

will vary dramatically, and cause problems to the Analog Bargraph.

Generally speaking, the Analog Bargraph display is approx. 50 digits. The accuracy requirement is not strict;

thus, the problem can be solved by using section approximation. That is to say, when measuring the resistor,

the operation of the Analog Bargraph can be processed under the following three conditions:

FS970X データシート(PDF) 29 Page - Fortune Semiconductor Corp.