A low voltage reference can be constructed using two small ICs and a few external resistors, cutting down on the current consumption from an average of about 440 µA of quiescent current to a meager 2.4µA. This low voltage reference circuit can be particularly useful in power constrained devices such as PDAs and inventory control units improving their battery life.

Although the lower voltage reference circuits have been in existence since the birth of the bandgap cell, the inferior line and load regulation than the high power consuming circuits was a major drawback. Modern op amps which draw low current have enabled the design of low voltage reference circuits which provide excellent line and load regulation and enhanced performance. This ultra-low-power reference circuit combines a shunt reference and an op amp. These modern designs combine a low power shunt reference with an ultra low power op amp to significantly reduce current consumption in voltage reference circuits.

This circuit is based on the MAX6006 1µA, +1.25V shunt reference, which provides minimal line-regulation error as it draws bias current directly from the amplified reference voltage. Load and line regulation is greatly improved from the resistively biased bandgap references due to the use of the MAX4470 op amp to supply the load current. . Line regulation is 90dB from VIN = 2.2V to 5.5V, and load regulation (with VIN = 2.5V) is 1µV per 10µA of output current and the total supply current is 2.4 µA.

Read and download: http://pdfserv.maxim-ic.com/en/an/AN834.pdf