# Voltage Reference Fundamentals: The Series Reference Design Equations

From Maxim Integrated Application Note 4003:

A series reference design is fairly easy. Just make sure the input voltage and power dissipation are within the maximums specified for the IC:

P_SER = (VSUP – VREF )IL + (VSUP × IQ )

For a series reference, the worst-case power dissipation occurs for maximum power-supply voltage and maximum load:

WC_P_SER = (VMAX – VREF )ILMAX + (VMAX × IQ )

where:

P_SER = power in series reference

VSUP = power-supply voltage

VREF = reference output voltage

IQ = reference quiescent current

WC_P_SER = worst-case power in series reference

VMAX = maximum power-supply voltage

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## 3 comments on “Voltage Reference Fundamentals: The Series Reference Design Equations”

1. etnapowers
May 20, 2014

WC_P_SER = (VMAX – VREF )ILMAX + (VMAX × IQ )

A solution to minimize the WC_P_SER  is to have a very low series resistance, then the difference VMAX – VREF will be minimum and, at the same time, by providing a good shutdown procedure to minimize the quescient current of the reference.

2. Davidled
May 20, 2014

Worst case circuit analysis is one of interesting area including power dissipation. Junction temperature factor such as Tj might be included in the equation.  A few components are sensitive to temperature. Equation would be nonlinear differential formulation.

3. etnapowers
June 11, 2014

@DaeJ: the junction temperature plays a role in the power dissipation of the single component of the IC, for the Voltage Reference the balance of power supplied and absorbed is the best way to evaluate the efficiency. The worst case is the most interesting case, as you correctly said.

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