DA6505.005

11 June 2018

34 (44)

AFE AND ADC INPUT SIGNAL RANGE DEFINITIONS

The MAS6505 has PI and NI input pins which allow measuring differential sensor bridge signal with both positive

and negative polarities. The differential input signal VIN is defined as voltage difference between positive (PI) and

negative (NI) input pin voltages VPI and VNI respectively.

VNI

VPI

VIN

−

=

Equation 2

Overall minimum and maximum differential input signals are defined by AFE GAIN and ADC OFS% settings as

follows.

GAIN

OFS

ISRADC

VIN

MIN

/

%

100

%

2

1













+

−



=

Equation 3

GAIN

OFS

ISRADC

VIN

MAX

/

%

100

%

2

1













+

+



=

Equation 4

where

ISRADC = 1400mV Overall input signal range of ADC

OFS% = -49% .. +49% ADC offset setting in percentage

GAIN = ±(1x .. 55.8x) AFE gain setting

Overall input signal range (ISR) of the MAS6505 is difference between maximum and minimum allowed

differential input signals.

GAIN

ISRADC

VIN

VIN

ISR

MIN

MAX

=

−

=

Equation 5

The ISRADC corresponds to overall input signal range of the ADC but from which 80% is considered linear

(ISRLINADC) and suitable for accurate measurements.

ISRADC

ISRLINADC



=

%

80

Equation 6

The AFE gain and ADC offset settings should be chosen so that minimum and maximum sensor signal voltages

differential input signals in the linear input signal range are as follows.

GAIN

OFS

ISRADC

VINLIN

MIN

/

%

100

%

2

%

80













+

−



==

Equation 7

GAIN

OFS

ISRADC

VINLIN

MAX

/

%

100

%

2

%

80













+

+



==

Equation 8

Linear input signal range (ISRLIN) is difference between maximum and minimum allowed differential input signals

which are in the linear signal range of the MAS6505. Signal distortion occurs beyond this signal range due to

increased non-linearity.

GAIN

ISRADC

GAIN

ISRLINADC

VINLIN

VINLIN

ISRLIN

MIN

MAX



=

=

−

=

%

80

Equation 9

to increased non-linearity.

Example

Temperature signal settings: OFST%=-7%, GAINT=+18.9

 -42.2mV

 +31.9 mV

 -34.8mV

 +24.4mV