DA6505.005
11 June 2018
FUNCTIONAL DESCRIPTION (continued)
Trimming operating modes
MAS6505 has trimming settings for the internal clock
oscillator, temperature sensing, AFE and ADC.
These are needed for example to fit sensors’ signals
with the input range of MAS6505 and to maximize
the noise performance.
temperature sensing, AFE and ADC have the right
trimming settings during each measurement. Thus
the end user of a trimmed sensor system only needs
to start measurement(s) at the selected configuration
settings and read the result(s).
There are five trimming setting registers and
corresponding EEPROM addresses. See table 1.
Four of these are for the AFE, ADC and temperature
sensor trimming settings. See tables 7-10. The fifth
is for internal clock oscillator which should be left
untouched since it is factory trimmed. See table 11.
The corresponding EEPROM trimming setting
addresses are for storing the trimming settings to the
non-volatile memory.
The other two trimming setting operating modes are
only for search of the optimal trimming values. In the
TRIM=01 or 10 setting only internal clock oscillator
trimming setting is read from the EEPROM but the
temperature sensing, AFE and ADC trimming
settings are taken from the registers. This allows fast
search of trimming settings via registers since the
slower EEPROM write procedure is not necessary
until only when the final trimming values are found.
The third TRIM=11 trimming setting operating mode
should not be used since it is only for factory
trimming of the internal clock oscillator.
MAS6505 has three trimming setting operating
modes which are selected by TRIM bits in the Trim
and test register (FA/7AHEX). See table 6. By default
the TRIM=00 which is the normal trimming operating
mode in which all the trimming settings will be
automatically read to registers from the EEPROM
memory in the beginning of each measurement. This
guarantees that the internal clock oscillator,
The Trim and test register (FA/7AHEX) contains also
SOSC, STEST and SCALC bit settings. These are
only for testing purposes and default zero bit values
should be always used (SOSC=0, STEST=0000,
SCALC=0).
Temperature sensing
MAS6505 supports two different temperature
sensing methods. The first method is based on
sensing sensor bridge resistance which changes in
temperature. Nominal sensor bridge resistance
values from 3 kΩ up to 6 kΩ including typical
resistance tolerances are supported. However other
sensor resistance values may also be possible just
by choosing low or unity gain amplification at the
analog front end (AFE) amplifier but at cost of
reduced measurement resolution.
from the temperature sensing diode during the
temperature
measurement.
The
external
temperature diode is connected between VDDS pin
(diode anode) and TD pin (diode cathode). To avoid
signal clipping GAINT=1, SGNGAINT=1 and
OFST%= -28% settings must be used in external
diode temperature measurement.
The temperature sensing method selection and
sensor bridge resistance trimming is done using
Temperature
sensor
configuration
register
The second temperature sensing method is using an
external temperature sensing diode. When selected
the MAS6505 sinks a constant 10 µA bias current
(FB/7BHEX). See table 7. The trimming value is stored
into EEPROM address (BB/3BHEX). See also chapter
Sensor bridge resistance temperature sensing.
11 (44)
MAS [ MICRO ANALOG SYSTEMS ]
