If I got it right, all intup and T+ T- too are provided internal protection diode for max continuaous current 20mA.
Tthese diodes allow on T+ T- vlong time voltage +-45V and short time ESD 2000V .
The first option to increase protection is add to input resistr for example R4,R5 20k , voltage lost for 20k and 20mA is 400V
i.e. voltage protection for long time willbe 400+45V , but the impact on ESD will be marginal.
the inserted resistors impair the thermal bond between the thermocouple end and the temperature sensor for compensation in MAX31856.
My idea is add ESB protection diode D3.
This diode increase ESD protection on 4kV human body modem and 15kV air, increase cuccent on long time, my estimate min by another 20mA.
disadvantages
- increase parasitic capacitance, I thing no problem, diode have max 200pA and on T+T- are 10nF C
- leacage current diode have max 300nA for 5V and on thermocouple id thecmocouple voltage +735mV BIAS I thing no problem but I am not sure
- something else ?
DRDY - in datasheet is not described in detail electrical chracteristic of this output. I theng stnadart outpit with pulup resistor and MOSFET which pulls the output to the ground. It is not a problem to connect several of them to one output, but I'm not sure yet again.