DA6505.005

11 June 2018

36 (44)

EXTERNAL TEMPERATURE DIODE TEMPERATURE SENSING

The MAS6505 supports temperature sensing using an external temperature sensing diode. This is selected by

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 @ 10

A) 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.

 +1092mV

 -308 mV

 +952mV

 -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]