ADM8660:  CMOS Switched-Capacitor Voltage Converter w/ Low Power Shutdown Pin

The ADM660/ADM8660 is a charge-pump voltage converter that can be used to either invert the input supply voltage giving V_OUT = -V_IN or double it (ADM660 only) giving V_OUT = 2 x V_IN. Input voltages ranging from +1.5 V to +7 V can be inverted into a negative -1.5 V to -7 V output supply. This inverting scheme is ideal for generating a negative rail in single power supply systems. Only two small external capacitors are needed for the charge pump. Output currents up to 50 mA with greater than 90% efficiency are achievable, while 100 mA achieves greater than 80% efficiency.

A Frequency Control (FC) input pin is used to select either 25 kHz or 120 kHz charge-pump operation. This is used to optimize capacitor size and quiescent current. With 25 kHz selected, a 10 µF external capacitor is suitable, while with 120 kHz the capacitor may be reduced to 2.2 µF. The oscillator frequency on the ADM660 can also be controlled with an external capacitor connected to the OSC input or by driving this input with an external clock. In applications where a higher supply voltage is desired it is possible to use the ADM660 to double the input voltage. With input voltages from 2.5 V to 7 V, output voltages from 5 V to 14 V are achievable with up to 100 mA output current.

The ADM8660 features a low power shutdown (SD) pin instead of the external oscillator (OSC) pin. This can be used to disable the device and reduce the quiescent current to 300 nA.