The LM2660/LM2661 switched capacitor voltage converter is a CMOS charge pump voltage converter that inverts a positive voltage in the range of 1.5V to 5.5V to the corresponding negative voltage. The LM2660/LM2661 uses two low cost capacitors to provide 100mA of output current without the cost, size, and EMI related to inductor based converters. With an operating current of only 120µA and operating efficiency greater than 90% at most loads, the LM2660/LM2661 provides ideal performance for battery powered systems. The LM2660/LM2661 may also be used as a positive voltage doubler. The oscillator frequency can be lowered by adding an external capacitor to the OSC pin. Also, the OSC pin may be used to drive the LM2660/LM2661 with an external clock. For LM2660, a frequency control (FC) pin selects the oscillator frequency of 10kHz or 80kHz. For LM2661, an external shutdown (SD) pin replaces the FC pin. The SD pin can be used to disable the device and reduce the quiescent current to 0.5µA. The oscillator frequency for the LM2661 is 80kHz.
The LM2660 and LM2661 are switched‑capacitor voltage converters that can invert a positive supply (1.5 V‑5.5 V) to a negative output or double the voltage for positive output. They use two low‑cost external capacitors, provide up to 100 mA of output current, and achieve typical conversion efficiencies of 88 % at 100 mA. The devices are offered in narrow SO‑8 and Mini SO‑8 packages.
Typical specifications include selectable oscillator frequencies of 10 kHz or 80 kHz, a typical output resistance of 6.5 Ω, and a very low quiescent current (120 pA for LM2661). The datasheet details pin functions, application circuits for negative‑voltage conversion, positive‑voltage doubling, and other uses such as voltage splitting, as well as guidelines for capacitor selection and device paralleling.
| Typical conversion efficiency (100 mA) | 88 % |
|---|---|
| Oscillator frequency (selectable) | 10 kHz or 80 kHz |
| Typical output resistance | 6.5 Ω |
For the LM2660, the FC pin selects 10 kHz when open or 80 kHz when tied to V+. For the LM2661 the oscillator runs at 80 kHz, or an external capacitor can be added to adjust the frequency.