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Providing power to the output of a power regulators


Full Member level 2
Mar 13, 2015
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Washington DC, USA
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Hello all,
This may be a super obvious question, but I just wanted to double check before I bring it up to the rest of my work colleagues, and come equipped with a good explanation as to why. We were working on a wideband communication system and are using a a whole host of development boards to make it happen, including a development board for a tunable filter chip, ADMV8818. The ADMV8818's development board has loads of power regulation on it in order to create 3 rails, 3.3, 2.5, and -2.5V (schematic below) (link here). During testing I always used the provided SMA connectors on the dev board to provide VPOS and VNEG to the inputs of the power regulators. However, now that we want to package the system in a chassis, the folks above me simply want to provide the correct rail voltages directly to the 8818 using the test points available on the development board, highlighted below.
Frankly I find this absurd, but it might be OK? below the schematic is the block diagram for the 3.3V power regulator. With no power to the chip, the gate of the output pchannel fet would be floating and Vds would be negative? Looking at FET IV curves, a negative Vds would imply zero current through the device? The outputs of the other two power regulators are similar, however, the negative voltage regulator as a N-channel MOSFET on its output.



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