What the 50 mA output and bipolar configuration mean for your rail
The MAX860IUA+: The ratiometric topology means the output voltage is a fixed multiple of the input — either -Vin (inverted) or 2Vin (doubled) — set by the pin configuration, not an external resistor divider. This makes it a compact, low-part-count solution for generating a negative rail or a boosted positive rail in mixed-voltage systems. The 50 mA current ceiling is the continuous output limit; the actual load current the part can sustain depends on the switching frequency selected and the flying capacitor value. At the lowest 6 kHz switching rate, the output impedance is higher, so the available current at the rated output voltage is lower than at 130 kHz. For a 50 mA load, use the 130 kHz pin-strap option and a low-ESR ceramic capacitor to keep ripple under control.
Switching frequency selection and capacitor sizing
Three pin-selectable switching frequencies — 6 kHz, 50 kHz, and 130 kHz — let the designer trade off output ripple against capacitor size and quiescent current. At 130 kHz, the flying and output capacitors can be as small as 0.22 µF ceramic, keeping the total BOM footprint under 10 mm². Dropping to 6 kHz cuts the switching losses but requires 10 µF electrolytics to hold the output ripple within 100 mV at full load. The part does not use synchronous rectification, so the Schottky diode drop (typically 0.4 V at 50 mA) subtracts from the output voltage in the inverting configuration. For a -5 V output from a 5 V input, budget 0.4 V headroom — the actual output settles at about -4.6 V under load unless the input is raised to 5.5 V.
Housed in the 8-uMAX/uSOP package (3.00 mm × 3.00 mm body, 0.65 mm pitch), the MAX860IUA+ occupies a standard MSOP-8 footprint. The tube delivery means the parts arrive in anti-static tubes of 50 or 100; for reflow, the MSOP-8 body handles standard lead-free profiles with a 260 °C peak. Operating temperature range is -25 °C to +85 °C, covering most commercial and industrial indoor environments. The part is rated for continuous operation at 85 °C ambient; above 70 °C the output current should be derated per the thermal impedance of the PCB copper pour under the package.
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