Charge pump converts –5V to 5V

Versatile switched-capacitor charge-pump voltage converters can provide a negative supply voltage from a positive-voltage source or double a positive source's voltage. However, certain applications that consist entirely of ECL (emitter-coupled-logic) circuits provide only a negative-voltage supply—for example, –5.2V. Figure 1 shows how you can use a switched-capacitor converter to obtain a positive power-supply voltage suitable for powering ECL-to-TTL (transistor-to-transistor-logic)-level translators and other circuits.

Although connections to IC₁ may appear to be reversed, the bilateral characteristics of IC₁'s internal switches allow use of IC₁'s output pin as its power input. Capacitor C₁ acquires a charge when IC₁'s internal switches connect the CAP+ pin to ground and CAP– to the negative-voltage power source via the output pin, OUT. During the next half-cycle, IC₁ connects CAP– to ground and CAP+ to IN (normally used as the input), transferring C₁'s positive charge to output capacitor C₃ and the load. With FSEL connected to OUT, an internal oscillator sets the charge-discharge cycle's frequency to approximately 1 MHz.

As Figure 2 shows, IC₁'s switches present internal resistances that affect the output voltage's magnitude, which is lower than the input voltage and subject to less-than-ideal regulation as output-load current increases. For optimum performance, use low-ESR capacitors for C₁, and input and output bypass capacitors C₂ and C₃.