MAS6505 datasheet(11/44 Pages) MAS

11 / 44 page

DA6505.005

11 June 2018

11 (44)

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 sensor

s’ signals

with the input range of MAS6505 and to maximize

the noise performance.

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.

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,

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).

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.

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.

The second temperature sensing method is using an

external temperature sensing diode. When selected

the MAS6505 sinks a constant 10 µA bias current

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

(FB/7BHEX). See table 7. The trimming value is stored

into EEPROM address (BB/3BHEX). See also chapter

Sensor bridge resistance temperature sensing.

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