DA6505.005
11 June 2018
FUNCTIONAL DESCRIPTION (continued)
Analog front-end and ADC trimming
The pressure and temperature sensors are
interfaced with analog front-end (AFE) which
comprises of a low noise chopper amplifier with 32
selectable gain options from 1x up to 55.8x and an
input signal polarity selection. The amplified sensor
signal is then fed to input of the delta-sigma (ΔΣ)
analog-to-digital converter (ADC). The input signal
range of the ratiometric ADC is ISRADC=1400 mV
at the nominal sensor supply voltage VDDS=1.68 V.
This corresponds to differential signal ranging from -
700mV to +700mV. The ADC offers eight input offset
options with both polarities to adjust to different
sensor signals.
the ADC. The ISRLIN is 10%...90% of the ISR i.e.
ISRLIN = 80%*ISR = 1120 mV at VDDS=1.68 V. See
further details in chapters AFE AND ADC INPUT
SIGNAL RANGE DEFINITIONS and AFE GAIN AND
ADC OFFSET SELECTIONS.
MAS6505 has individual AFE and ADC trimming
settings for both pressure and temperature
measurement. The AFE gain and polarity for
pressure is trimmed using Pressure gain trim register
(FC/7CHEX). See table 8. The corresponding
EEPROM storage address is (BC/3CHEX). The AFE
gain and polarity for temperature is trimmed using
Temperature gain trim register (FD/7DHEX). See table
9. The corresponding EEPROM storage address is
(BD/3DHEX). The ADC offsets and polarities for
pressure and temperature are trimmed using
Temperature and pressure offset trim register
(FE/7EHEX). See table 10. The corresponding
EEPROM storage address is (BE/3EHEX).
For the best resolution and to avoid signal clipping
the amplifier gain and the ADC offset settings need
to be trimmed optimally for both the temperature and
the pressure sensor signals. In optimal cases the
signal ranges of amplified sensor signals cover
maximally the linear input signal range (ISRLIN) of
Internal clock oscillator
MAS6505 has an internal clock oscillator making
external clock unnecessary. In the forced mode it is
turned on only during the A/D conversions and
turned off when the sleep mode is entered. In the
normal mode the internal clock oscillator is turned on
continuously to run selected measurements
periodically.
The internal oscillator frequency is factory trimmed
to 250 kHz using a 7-bit register. See table 11 for
Clock oscillator frequency trim register (FF/7FHEX).
The factory trimming value has been stored into
EEPROM address (BF/3FHEX). Note: it is
recommended to not touch the factory trimming
value of the internal clock oscillator. The converter
runs from a divided system clock which is 125 kHz.
EEPROM memory
The 512-bit (64 byte) EEPROM memory is available
for storing trimming and calibration data on chip. Six
of the EEPROM bytes are reserved for trimming
purposes. One byte is for selecting temperature
sensor and trimming sensor bridge resistance that is
used in sensor bridge resistance based temperature
measurements. Three bytes are for trimming AFE
gain and ADC offset in the pressure and temperature
measurements. Two EEPROM addresses are
reserved for storing factory trimming values of
EEPROM oscillator and internal clock oscillator.
These EEPROM addresses must be left untouched.
The remaining 464 bits (58 bytes) in addresses
80/00HEX … B9/39HEX are free for other use such as
storing sensor calibration coefficients. See table 1.
After power on reset the EEPROM is by default
inactive. To use EEPROM (read or write) it needs to
be first activated. To prevent accidental overwriting
or erasing of the trimming and calibration memory
the EEPROM write requires an additional enable
setting. These EEPROM functions are controlled
using EEPROM control register (ED/6DHEX). See
table 2 for EON and EWE bit settings. When
activated the EEPROM draws typically 60µA current.
To save current the EEPROM should be always
disabled after use.
See also chapters EEPROM WRITE PROCEDURE
and EEPROM READ ONLY PROCEDURE.
Calibration
MAS6505 performs pressure and temperature
measurements resulting raw measurement values.
Thus calibrated temperature and pressure reading
calculations need to be done outside in the host
system by utilizing calibration coefficients that are
stored into the EEPROM during sensor calibration
procedure. See additional DAE6505 document
regarding sensor system calibration.
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MAS [ MICRO ANALOG SYSTEMS ]
