DA6505.005
11 June 2018
EXTERNAL TEMPERATURE DIODE TEMPERATURE SENSING
The MAS6505 supports temperature sensing using an external temperature sensing diode. This is selected by
setting TSENSOR=1 in the Temperature sensor configuration register (FB/7BHEX). In this configuration the
external temperature sensing diode is connected between VDDS (anode) and TD (cathode). During temperature
measurement the MAS6505 sinks a constant 10 µA bias current from the external temperature sensing diode and
the temperature dependent diode forward voltage (VF~390mV @ 10A) is measured.
Figure 11. External temperature diode temperature sensing circuit illustration
The external temperature diode forward voltage has roughly -2.2mV/C temperature dependency as follows.
VF(T)=390mV-2.2mV/°C*(T-25°C)
Equation 14
Following AFE and ADC settings must be used to avoid external diode signal VF(T) clipping.
GAIN=-1 (GAINT= 1, SGNGAINT=1)
OFS%=100%*(-390mV)/1400mV -28% => OFST%= -28%
Unity AFE gain needs to be used to keep the large diode voltage within input signal range of the ADC. Negative
gain value is for achieving positive temperature dependency in the AD conversion result. The ADC offset setting
needs to be negative since the negative gain value reverses signal polarity at the ADC input. The above GAIN
and OFS% settings correspond to following input signal range limits.
VINMIN =1400mV*(-0.5-28%/100%)/(-1) +1092mV
VINMAX=1400mV*(0.5-28%/100%)/(-1) -308 mV
VINLINMIN =1400mV*(-0.5*80%-28%/100%)/(-1) +952mV
VINLINMAX=1400mV*(0.5*80%-28%/100%)/(-1) -168mV
From equation 14 we can calculate that the temperature diode signal is between 247mV and 533mV in
temperature range from -40°C to +90°C. Figure 12a shows falling temperature diode voltage signal VF (blue line)
and overall (red continuous lines) and linear (red dashed lines) input signal range limits.
Using equation 10 the corresponding ADC output code can be also calculated. Figure 12b illustrates ADC output
code showing desired positive temperature dependency. Figure includes also both overall (red continuous lines)
and linear (red dashed lines) input signal range limits as ADC code values.
Figure 12a. Temp diode VF signal [mV]
Figure 12b. ADC output code [dec]
36 (44)
MAS [ MICRO ANALOG SYSTEMS ]
