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Miniature, Precision Negative Reference Requires No Precisio

2015-02-28 04:22  
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Miniature, Precision Negative Reference Requires No Precision Resistors
Switched-capacitor charge-pumps, which occupy less space than do their inductor-based counterparts, are popular for providing inverted voltages in small hand-held equipment. Combining a switched-capacitor charge-pump with a precision reference, for example, yields an inverted reference from a positive power supply (Figure 1). Unlike the more typical combination of a positive 3-terminal reference and an op-amp inverter, this one delivers accurate inversions without the need for precision resistors and a negative supply. The charge-pump inverter (U2) delivers -5V by inverting the output of a 5V precision reference (U1). U1 accepts inputs between 5.2V and 12.5V. Replacing it with a 2.5V reference that accepts 2.7V to 12.5V, as in the MAX6125, produces a -2.5V output. This circuit is very compact. It needs only three surface-mount capacitors, and the ICs occupy tiny SOT23 packages.