# Voltage calculations for FK33

## VCCINT

Taking into account the two equations for resistance calculation (reciprocal sum for parallel, straight sum for series) and knowing that the formula for VCCINT is as follows:

Knowing that the value and placements of the named resistors in a SQRL FK33's voltage sense circuit are as follows:

By their placements, we can deduce that:

And by substituting the resistors with their values, we can calculate that:

and that:

By looking at the rheostat's datasheet, we can confirm that the resistance value for any given VID is as follows:

The datasheet for the MCP4552T-503E states the following typical resistance value for the part, with a tolerance of +/- 20%:

With that information, we can replace the value of tAB in the rheostat calculation with the value 50.

Simplifying the above equations, we can arrive at the conclusion that, with the resistor values in the SQRL FK33 and the typical resistance value of MCP4552T-503E, the equation to arrive at VCCINT is:

## VCCHBM

For VCCHBM, the voltage calculation is the same; the only thing that changes is how we define R1 and Radj.

In the case of VCCHBM, the resistance values and placements are as follows:

Leading us to these definitions:

The rheostat used for VCCHBM is the same as VCCINT's, the MCP4552T-503E. Therefore, we can use the same formula to calculate its resistance for any given VID.

We can then simplify R1 and Radj by substituting their resistor values to leave Rrheo as the only variable:

Arriving at the final formula, with D as the only remaining variable required to calculate VCCHBM.

## VCCBRAM

VCCBRAM is very similar to the earlier two. Again, the voltage calculation is the same; the only thing that changes is how we define R1 and Radj.

In the case of VCCBRAM, the resistance values and placements are as follows:

Leading us to these definitions:

The rheostat used for VCCBRAM is, once again, the MCP4552T-503E. Therefore, we can use the same formula to calculate its resistance for any given VID.

Simplifying:

Arriving at the final formula, with D as the only remaining variable required to calculate VCCBRAM.