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Showing posts from February, 2017

Inverting And Combining An Open-Drain Signal

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Lately, I have been working with the LTC4151-1 chip by Linear Technology.  It is used to measure voltage and current with high resolution typically in telecommunications equipment.  In the process of validating my design, I need to test it with the simplest circuit possible in order to simplify fabrication and eliminate variables introduced by other intermediate devices (namely, the required optoisolators).

The LTC4151-1 chip communicates over the I2C bus.  Only problem: its setup breaks out the SDA (serial data) signal into SDAI (data in from the microcontroller) and /SDAO (data out to the microcontroller, inverted).  It is broken out like this (with SDAO inverted) so that people can conveniently wire up optoisolators to reconcile different ground potentials that exist between the MCU and the unit whose voltage is being measured.  (Many times, the V- out of the battery will not be the same as the GND used by your microcontroller logic, computer, or etc., especially if you are measurin…