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# AD7705 - current drawn by reference input

Hello,

I want to use a shunt reference voltage to generate 1.225V, as demanded in the AD7705's datasheet. However, to calculate the required impedance before the shunt I need to know the maximum current drawn by the load (in this case the AD7705). This is not given in the datasheet, though. If I assume it to be much smaller than the minimum current drawn by the shunt (45µA) and neglect it I get a value of:

R = ( V_min - V_ref ) / ( I_ref,min + I_load,max )
= (3.3V - 1.225V) / 0.000045A

= 46111 Ohm

However, with a resistor like this I don't get the desired 1.225V so what would be a better assumption or where can I get the exact value?

Regards,

Dominik

• Btw: I also tested it with a 30kOhm resistor. In both cases, I get an output voltage in the range of 3.25V.

• I found out how to calculate the drawn current: the resistance of the reference input is given in the datasheet with 5kOhm.

However, the LM4041 I received had different pins than stated in its datasheet. Hence, all the problems!