Maxim Integrated Application Note 4003 explains the fundamentals of the Series Voltage Reference:
A series reference has three terminals: VIN, VOUT, and GND. Though similar in concept to a linear voltage regulator, it is designed for lower current and higher accuracy. A series reference operates in series with the load (Figure 1), and can be regarded as a voltage-controlled resistance between the VIN and VOUT terminals. It regulates by adjusting its internal resistance such that VIN minus the drop across the internal resistance equals the reference voltage at VOUT. Because current flow is necessary to generate a voltage drop, the device draws a small quiescent current to ensure regulation when the load is removed. Series references have the following characteristics:
- The power-supply voltage (VCC) must be high enough to allow a voltage drop across the internal resistance, but not high enough to damage the reference IC.
- The IC and its package must handle power dissipation in the series pass element.
- With no load current, the only source of power dissipation is the reference IC's quiescent current.
- Series references generally have a better initial tolerance and temperature coefficient than do shunt references.
This is the first fundamental on references leading up to our Ask the Experts session on Wednesday, May 21, at 1:00 p.m. EDT (10:00 a.m. PDT). You can sign in using this link on May 21, and you can even enter questions ahead of time.