AME811A AME [Analog Microelectronics], AME811A Datasheet - Page 11

• Manufacturer Part Number: AME811A
• Description: 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs
• Manufacturer: AME [Analog Microelectronics]

AME811/AME811A/AME811R
Integrating Capacitor (Cint)
Cint should be selected to maximize the integrator out-
put voltage swing without causing output saturation. A
if “ANALOG COMMON” is used as signal reference.
For 3 readings/second (fosc = 48 KHz) a 0.22 F value
is suggested. If a different oscillator frequency is used,
Cint must be changed in inverse proportion to maintain
the nominal
sion for Cint is:
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 A quiescent current.
The integrator and buffer can supply 20 A 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 ; 2.0V full-scale requires 470K .
Summary of component selection:
Note: fosc = 48 KHz
2V full-scale integrator output swing is recommended
Cint = [(4000)(1/fosc)(Vfs/Rint)] / Vint
F u l l s c a l e
where:
C a z
R i n t
C i n t
V r e f
fosc= Oscillator clock frequency
Vfs = Full-scale input voltage
Rint = Integrating resistor
Vint = Desired full-scale integrator output swing
Analog Microelectronics, Inc.
2V integrator swing. An exact expres-
2 0 0 . 0 m V
1 0 0 . 0 m V
0 . 4 7 F
0 . 2 2 F
4 7 K
0 . 0 4 7 F
4 7 0 K
0 . 2 2
2 . 0 0 0 V
1 . 0 0 0 V
F
With HOLD And Differential Reference Inputs
Oscillator Components
R-C Oscillator
A 100 K
Cosc is selected by using the equation:
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:
For 50 Hz rejection:
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/in
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 . 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.
Low Battery Flag (LB)
The low battery flag is set when the supply voltage (V+
to V-) is lower than seven volts, typical. Once the LB is
set, the waveform of the LB will be out of phase with
the BP (Back Plane) to turn on a low battery annuncia-
tor for AME811.
F u l l -S c a l e V o l ta g e
2 0 0 . 0 m V
2 . 0 0 0
40KHz, 48KHz, 60KHz etc.
40KHz, 50KHz, 66-2/3KHz etc.
3-1/2 Digit A/D Converter - Low Power
fosc = 0.45/(RC)
Rosc is recommended for all frequencies.
V
V r e f
1 0 0 . 0 m V
1 . 0 0 0
2
. Rather
V
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