Electronic Design

50-MHz Op Amps Self-Calibrate Offset

The MCP65X 50-MHz rail-to-rail operational amplifiers from Microchip Technology include an on-chip “mCal” calibration circuit that calibrates offset voltage at powerup or on-command. An internal power on-reset detector or a signal on an external pin initiates calibration. Self-calibration provides a lower initial voltage offset than conventional op amps, along with a means to continually control drift over time and temperature, Microchip says (see the figure). Target applications include microphone preamplifiers, optical detector circuitry, medical devices, digital scales, H-bridge drivers, barcode scanners, and transmission-line drivers.

The guaranteed minimum and maximum offset voltage after calibration are -200 and +200 µV. Calibration step size is typically 37 µV. Typical drift is ±2.5 µV/°C. Typical input bias current is 6 pA at room ambient temperature and 130 pA at 85°C, and it rises to a guaranteed maximum of 5000 pA (1700 pA typical) at 125°C. Typical harmonic distortion plus noise is 0.0012%. Maximum output drive is 95 mA.

There are three versions. The MCP651 is a single op amp, whi l e the MCP652 and MCP655 are duals. The MCP651 single and MCP655 dual have external calibration pins, while the MCP652 dual calibrates only on startup.

Free, downloadable Microchip support software includes the FilterLab analog filtering software tool and the Mindi online simulator tool. FilterLab generates schematic diagrams of filter circuits with component values and di splays the f requenc y responses. Mindi generates circuit diagrams and adds simulation for active-filter, amplifier, and power-management applications

Housed in an eight-pin SOIC, the MCP651 costs $1.21 each. The MCP652, also in an eightpin SOIC, costs $1.49. In a 3- by 3-mm DFN, they cost $1.55. The MCP655comes in a 10-pin MSOP and in 3- by 3-mm DFN packaging for $1.58 each. All prices are for 10,000-unit quantities.



TAGS: Microchip
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