Charge pump for bipolar rails — what the ratings mean
The MAX860ISA+T is a charge-pump voltage converter from Maxim Integrated that generates a regulated output from a single input supply. It can produce either a negative voltage equal to -Vin or a doubled positive output of 2Vin, selected by pin-strapping. Input range spans 1.5 V to 5.5 V (with a separate 2.5 V minimum for the doubler mode), and the part delivers up to 50 mA. Three switching frequencies — 6 kHz, 50 kHz, and 130 kHz — are selectable via a logic pin, letting you trade ripple for capacitor size. The 8-SOIC package fits standard surface-mount layouts, and the operating temperature range of -25°C to 85°C covers most indoor and industrial ambient conditions.
Switching frequency — ripple vs. board space
Three frequency options let you choose: 6 kHz for lowest quiescent current and minimal switching noise (good for audio or low-speed analog), 50 kHz as a general-purpose middle ground, and 130 kHz for smallest external capacitors. Higher frequency reduces capacitor value and board area but increases switching losses and output ripple. The trade-off is standard for charge-pump designs — plan your capacitor dielectric (X5R or X7R) to handle the ripple current at the selected frequency.