Claudio,
The TPS77733 is a fast transient response Linear Dropout Regulator. Regular LDO's are fairly good as noise filters up to a few MHz. Because this one is designed for fast transient response, it is not quite as effective as a noise filter. Almost any standard LDO that meets your input voltage, output voltage and current requirements will give you decent performance. There are literally hundreds to choose from, so it depends on the amount of space you have, etc. You might also want to put a ferrite bead in series with the power supply pins of the MSP. This will filter any high-frequency noise. However, it only filters noise that is coming in from the power supply. A bigger problem is the internal digital switching noise generated by the MSP. Trying to get very good, low noise performance on an ADC that is in the same chip as a microprocessor is a compromise at best. Make sure your capacitors are low-ESR (e.g. ceramic or polymer tantalum), and that they are placed as close as possible to the supply pins of the MSP. Also, watch out for "false" noise picked up by your scope ground lead. Keep this lead as short as possible and use a ground as close as possible to the MSP VSS pins (a short wire soldered to the negative side of one of the decoupling caps is good). Hope this helps. Good luck. Warren -----Original Message----- From: mspgcc-users-ad...@lists.sourceforge.net [mailto:mspgcc-users-ad...@lists.sourceforge.net] On Behalf Of Claudio Grasso Sent: Wednesday, August 18, 2004 4:27 PM To: 'mspgcc-users@lists.sourceforge.net' Subject: [Mspgcc-users] Low noise power supply. Hi all! I am trying to build an application that uses the ADC12 and I need a low noise power supply. I am using a TPS77733 regulator but it has a high frequency noise of about 10mV uncharged (in the oscilloscope one can see regular isolated pulses). When I charge it with an MSP430f149, noise increases up to 20 mV peak to peak (but now you don't see isolated pulses but a regular oscillation -reflecting the MSP operation for sure- ). This variation is also reflected in Vref and results in fluctuations in measurements of steady voltages. Can anybody please suggest me where to find an example of a low noise power supply? I've been searching in the application notes but I only found examples powered by batteries (what is not an option in my case). I can't understand either, why the noise in the output of the TPS increases so much when charged by the MSP (it drains just a few uA). My test circuit has all the capacitors suggested in the User guide. Any help will be greatly welcome. Best regards, Claudio PS: Sorry this is quite off topic but I'm really lost :-(
