DA6502.008
29 November 2012
APPLICATION INFORMATION
Input Signal Range Definitions
The input signal voltage polarity is from positive input PI to the negative input NI. MAS6502 has input signal
range (ISR) and offset (OFFSET) selection options that determines the input signal range of the A/D converter.
The minimum and maximum input signal values in the linear input signal range (ISRLIN) are calculated as
follows.
ISRLIN
VIN _ MIN = OFFSET −
VIN _ MAX = OFFSET +
Equation 1.
Equation 2.
2
ISRLIN
2
Table 11 shows minimum and maximum input signal values in the linear input signal range at different input
signal range and offset selection combinations.
Table 11. Minimum and maximum input signal values in the linear input signal range
VIN_MIN
[mV]
OFFSET
[mV]
ISR
[mV]
ISRLIN
[mV]
VIN_MAX
[mV]
0
33
0
33
0
33
0
33
325
325
220
220
150
150
100
100
260
260
176
176
120
120
80
-130
-97
-88
-55
-60
-27
-40
-7
130
163
88
121
60
93
40
73
80
The digital A/D conversion result, CODE, depends on the input signal as follows.
VIN − OFFSET
CODE = CODE MAX ⋅ 0.5 +
⋅
Equation 3.
ISR
CODE = digital A/D-conversion output code
CODE MAX = A/D-converter maximum code (minimum code is zero)
See page 4 Electrical Characteristics for CODE MAX values at different over sampling ratio (OSR) selections.
Pressure Measurement Configuration
Piezoresistive absolute pressure sensor can be modeled roughly with following signal voltage characteristic
when including only first order pressure and temperature characteristics..
FS ⋅
1+ TCFS
⋅
VDD
VIN
(
p,T
)
=
⋅
⋅ p + OS ⋅
(
1+ TCOS
⋅
(
T −TREF ))
Equation 4.
VDDREF
pFS
VDD = supply voltage
VDDREF = reference supply voltage at which the sensor parameters (FS, OS) have been specified (often 5V)
p = pressure [bar]
pFS = full-scale pressure range [bar]
FS = full-scale span [V]
OS = zero pressure offset [V]
TCFS = full-scale span temperature coefficient [ppm/°C]
TCOS = offset temperature coefficient [ppm/°C]
TREF = reference temperature for resistor values [°C]
T = actual temperature to be measured [°C]
The above linear approximation includes sensor full-scale span and offset signal temperature dependencies.
14 (20)
MAS [ MICRO ANALOG SYSTEMS ]
