AME7106 datasheet(12/20 Pages) AME

12 / 20 page

AME, Inc.

AME7106/AME7106A/AME7106R

AME7107/AME7107A/AME7107R

3-1/2 Digit A/D Converter

High Accuracy, Low Power

F u l l sc al e

2 0 0 . 0 m V

2. 0 00V

Ca z

0 . 4 7

µ F0 . 0 4 7 µ F

R i nt

47 K

Ω

47 0 K

Ω

C i nt

0. 2 2

µ F0 . 2 2 µ F

V r e f

10 0. 0m V

1 . 0 00V

Oscillator Components

R-C Oscillator

A 100 K

Ω Rosc is recommended for all frequencies.

Cosc is selected by using the equation:

fosc = 0.45/(RC)

For fosc of 48KHz, Cosc is 100pF nominally.

To achieve maximum line noise rejection, the signal-

integrate period should be a multiple of line period. The

optimum oscillator frequencies for 60 Hz and 50 Hz

rejection are listed as follows:

For 60 Hz rejection:

40KHz, 48KHz, 60KHz etc.

For 50 Hz rejection:

40KHz, 50KHz, 66-2/3KHz etc.

Reference Voltage Selection

A full-scale reading (2000 counts) requires the input

signal be twice the reference voltage.

In some applications a scale factor other than unity may

exist between a transducer output voltage and the re-

quired digital reading. Assume, for example, a pres-

sure transducer output is 600 mV for 2000 Ib/in2. Rather

than dividing the input voltage by three the reference

voltage should be set to 300 mV. This permits the trans-

ducer input to be used directly. The integrator resistor

would be 120K

Ω. In some temperature and weighting

system with variable tare, the offset reading can be

generated by connecting the voltage transducer be-

tween INHI and COMMON and the variable offset volt-

age between COMMON and INLO.

F u ll-S c a le V o lta g e

V re f

20 0.0 m V

10 0.0 m V

2.0 00

1 .0 00

n Component Value Selection

Auto-Zero Capacitor (Caz)

The Caz capacitor size has some influence on system

noise. A 0.47

µF capacitor is recommended for 200 mV

full-scale applications. A 0.047

µF capacitor is recom-

mended for 2.0V full-scale applications. A mylar di-

electric capacitor is adequate.

Reference Capacitor (Cref)

A 0.1

µF capacitor is acceptable when “INLO” is tied

to analog common. If a large common-mode voltage

exists and the application requires 200 mV full-scale,

increase Cref to 1.0

µF. A mylar dielectric capacitor is

adequate.

Integrating Capacitor (Cint)

Cint should be selected to maximize the integrator out-

put voltage swing without causing output saturation. A

±2V full-scale integrator output swing is recommended

if “ANALOG COMMON” is used as signal reference.

For 3 readings/second (fosc = 48 KHz) a 0.22

µF value

is suggested. If a different oscillator frequency is used,

Cint must be changed in inverse proportion to maintain

the nominal 2V integrator swing. An exact expression

for Cint is:

Cint = [(4000)(1/fosc)(Vfs/Rint)] / Vint

where:

fosc= Oscillator clock frequency

Vfs = Full-scale input voltage

Rint = Integrating resistor

Vint = Desired full-scale integrator output swing

Cint must have low dielectric absorption to minimize

rollover error. A polypropylene capacitor is recom-

mended.

Integrating Resistor (Rint)

The input buffer amplifier and integrator both have a

class A output stage with 100

µA quiescent current.

The integrator and buffer can supply 20

µA drive cur-

rents with negligible linearity errors. Rint is chosen to

keep the output stage in the linear region. For a 200mV

full-scale, it is 47K

Ω; 2.0V full-scale requires 470KΩ.

Summary of component selection:

Note: fosc = 48 KHz

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