We use an ADR430B as the external reference. This device has an external trim adjust pin. The datasheet shows how to connect this to a pot for adjustment. We have been considering some possible circuits which would measure the temperature and then adjust this trim node to compensate. To do this, we would need additional information on the trim input. Regarding the trim pin, could you please tell us:
Can we drive the the pin with an opamp from a DAC?
Is it a voltage or a current input?
What is the input range?
What is the input impedance?
When we move the potentiometer to a higher voltage, does the ouput voltage of the ADR430B go up or down?
Is there an equation which relates the ouput voltage to the voltage or resistnace at the trim pin?
Thanks and Best Regards,
-Tim Starr on behalf of RD@AT
Apologies for the delayed response. I already contacted the application engineer for this product regarding your query. I will get back to you as soon as I hear from him. Also, if you look at figure 29, R2 and R3 are trimmed and the impedance of the trim pin varies from part to part. Because of this, there is no equation that relates to the output voltage.
Can I drive it with an opamp or some other device?
Driving the Trim pin with a source other than the voltage divider shown in the datasheet (Figure 34) is not recommended as it was not designed for that purpose and has never been tested or characterized.
Is it a voltage or current input?
The voltage on the Trim input creates a current through internal resistors.
What is its input range?
This has not been specified in any of the original design documentation because the input has a designated topology as shown in the datasheet.
The internal resistors are trimmed during production so they do not have a fixed resistance.
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