Dear all, My situation is to build a battery-powered sensoing device using MSP430F449 and I would like to use the build-in ADC to measure the 0- 3V analog data. We use a DC-DC convertor to provide a stable 3V to all the analog ICs and also I would like to fed it to AVCC and also use it as ADC 's reference. But the efficiency of the DC-DC convertor is not so good, so, I don't want to connect its output to DVCC to save power. And the DVCC uses the main battery supply (3V) which may be droped (~to even 2.6V) as the time passed. When I give 2.6V to DVCC and stable 3V to AVCC (AGND and DGND connected togather), the C-SPY cannot program the code to the internal flash memory. Does it mean that we MUST connect DVCC and AVCC together? We can't give 2 different 2 voltage level to them? Please comments. Thanks!! Danny Chow Electronic Engineer
Can I give 2 different voltage to DVCC and AVCC?
Started by ●July 23, 2003
Reply by ●July 23, 20032003-07-23
chowkamfai wrote: > Dear all, > > My situation is to build a battery-powered sensoing device using > MSP430F449 and I would like to use the build-in ADC to measure the 0- > 3V analog data. > > We use a DC-DC convertor to provide a stable 3V to all the analog > ICs and also I would like to fed it to AVCC and also use it as ADC 's > reference. Clean supplies are as important as stable ones. The internal 1.5V reference would seem a better choice for you. then you can run on batteries quite happily, use the internal power supply monitor to keep tabs on the supply voltage and still get good A/D results as the battery fades. > > But the efficiency of the DC-DC convertor is not so good, so, I > don't want to connect its output to DVCC to save power. And the DVCC > uses the main battery supply (3V) which may be droped (~to even 2.6V) > as the time passed. get a better one. You also need to study the data sheet more closely. It speciifes that no voltage applied to any pin should exceed Vcc by more than 0.3V, and that this is a maximum rating. ie you shouldn't design it with AVcc > Vcc. > > When I give 2.6V to DVCC and stable 3V to AVCC (AGND and DGND > connected togather), the C-SPY cannot program the code to the > internal flash memory. If you look at the specs for the MSP430Fxxx you will see that the minimum voltage for flash programming is 2.7V. personally I would recommend a minimum of 3.0V. Get another Dc/Dc converter. there are hundreds of different types out there, some rated up to 1A in tiny packages. Most of these are very efficient. > > Does it mean that we MUST connect DVCC and AVCC together? > We can't give 2 different 2 voltage level to them? Please comments. You can supply AVcc < DVcc but not the other way round. Al
Reply by ●July 23, 20032003-07-23
Thanks for your comment, onestone~ > Clean supplies are as important as stable ones. The internal 1.5V > reference would seem a better choice for you. then you can run on > batteries quite happily, use the internal power supply monitor to keep > tabs on the supply voltage and still get good A/D results as the battery > fades. The analog output is 0V-3V. So, using 1.5V internal reference is not suitable I think... > > get a better one. You also need to study the data sheet more closely. It > speciifes that no voltage applied to any pin should exceed Vcc by more > than 0.3V, and that this is a maximum rating. ie you shouldn't design it > with AVcc > Vcc. The device in fact is a electronic watch which uses a normal 2032 battery. So, I need try my best to minimize the power consumption. The low noise DC-DC convertor (TI TPS60243) is quite low in efficiency when the load is low. So, when the analog sensing part is off (most of the time), the watch is used as a normal clock. A minimal current is needed (e.g. <20 uA) at normal clock but it cannot be satisfied using this convertor. So, I prefer to use the battery directly as DVCC. Of course, I don't want to use too expensive DC-DC convertor. Datasheet said that ADC input can accept upto AVCC+0.3V. I just think that if we keep the AVCC at 3V even the DVCC is only 2.7V, my circuit can still accept the 0-3V analog ADC data accurately. > > If you look at the specs for the MSP430Fxxx you will see that the > minimum voltage for flash programming is 2.7V. personally I would > recommend a minimum of 3.0V. Get another Dc/Dc converter. there are > hundreds of different types out there, some rated up to 1A in tiny > packages. Most of these are very efficient. > You can supply AVcc < DVcc but not the other way round. >
Reply by ●July 23, 20032003-07-23
When I turn off the ADC part of the device, I would like to turn off also the 3V given to AVCC. Will the MSP430 stills operate? It seems that the AVCC also supplies to FLL+ and port 1... I think it may cause a problem. --- In msp430@msp4..., "chowkamfai" <chowkamfai@y...> wrote: > Thanks for your comment, onestone~ > > > Clean supplies are as important as stable ones. The internal 1.5V > > reference would seem a better choice for you. then you can run on > > batteries quite happily, use the internal power supply monitor to > keep > > tabs on the supply voltage and still get good A/D results as the > battery > > fades. > > The analog output is 0V-3V. So, using 1.5V internal reference is not > suitable I think... > > > > > get a better one. You also need to study the data sheet more > closely. It > > speciifes that no voltage applied to any pin should exceed Vcc by > more > > than 0.3V, and that this is a maximum rating. ie you shouldn't > design it > > with AVcc > Vcc. > > The device in fact is a electronic watch which uses a normal 2032 > battery. So, I need try my best to minimize the power consumption. > The low noise DC-DC convertor (TI TPS60243) is quite low in > efficiency when the load is low. So, when the analog sensing part is > off (most of the time), the watch is used as a normal clock. A > minimal current is needed (e.g. <20 uA) at normal clock but it cannot > be satisfied using this convertor. So, I prefer to use the battery > directly as DVCC. Of course, I don't want to use too expensive DC- DC > convertor. > > Datasheet said that ADC input can accept upto AVCC+0.3V. I just think > that if we keep the AVCC at 3V even the DVCC is only 2.7V, my circuit > can still accept the 0-3V analog ADC data accurately. > > > > > If you look at the specs for the MSP430Fxxx you will see that the > > minimum voltage for flash programming is 2.7V. personally I would > > recommend a minimum of 3.0V. Get another Dc/Dc converter. there are > > hundreds of different types out there, some rated up to 1A in tiny > > packages. Most of these are very efficient. > > You can supply AVcc < DVcc but not the other way round. > >
Reply by ●July 23, 20032003-07-23
chowkamfai wrote: > Thanks for your comment, onestone~ > > >>Clean supplies are as important as stable ones. The internal 1.5V >>reference would seem a better choice for you. then you can run on >>batteries quite happily, use the internal power supply monitor to > > keep > >>tabs on the supply voltage and still get good A/D results as the > > battery > >>fades. > > > The analog output is 0V-3V. So, using 1.5V internal reference is not > suitable I think... I use it to monitor 12V incoming supplies, simple resistro divider. > > >>get a better one. You also need to study the data sheet more > > closely. It > >>speciifes that no voltage applied to any pin should exceed Vcc by > > more > >>than 0.3V, and that this is a maximum rating. ie you shouldn't > > design it > >>with AVcc > Vcc. > > > The device in fact is a electronic watch which uses a normal 2032 > battery. So, I need try my best to minimize the power consumption. > The low noise DC-DC convertor (TI TPS60243) is quite low in > efficiency when the load is low. Check its current when in shut down. You will need to take that into consideration as well. > So, when the analog sensing part is > off (most of the time), the watch is used as a normal clock. A > minimal current is needed (e.g. <20 uA) at normal clock but it cannot > be satisfied using this convertor. So, I prefer to use the battery > directly as DVCC. Of course, I don't want to use too expensive DC-DC > convertor. Then don't use any, follow my first suggestion. use the battery directly. monitor it using the Vcc/2 multiplexed A/D signal then use the 1.5V internal reference for your analog reference. You still need to follow normal analog power supply rules, decouiple the AVcc supply separately from DVcc etc etc. I monitor Vin using nearly 1M voltage divider. It works quite happily and ensures low current. > > Datasheet said that ADC input can accept upto AVCC+0.3V. I just think > that if we keep the AVCC at 3V even the DVCC is only 2.7V, my circuit > can still accept the 0-3V analog ADC data accurately. Look in the absolute ratings it very clearly states that no voltage on any pin should exceed DVcc+0.3V That includes AVcc. All other ratings are subordinate to that. >>If you look at the specs for the MSP430Fxxx you will see that the >>minimum voltage for flash programming is 2.7V. personally I would >>recommend a minimum of 3.0V. Get another Dc/Dc converter. there are >>hundreds of different types out there, some rated up to 1A in tiny >>packages. Most of these are very efficient. >>You can supply AVcc < DVcc but not the other way round. Al
Reply by ●July 23, 20032003-07-23
chowkamfai wrote: > When I turn off the ADC part of the device, I would like to turn off > also the 3V given to AVCC. Will the MSP430 stills operate? > It seems that the AVCC also supplies to FLL+ and port 1... > I think it may cause a problem. Throw away the DC/Dc converter. You don't need it. All you need to do is ensure that you have 3V available for flash programming. DON'T TRY AND PROGRAM ON ANYTHING BUT BRAND NEW BATTERIES. In fact I would have a separate battery like a Li-Ion or LTC for programming. Al > > --- In msp430@msp4..., "chowkamfai" <chowkamfai@y...> wrote: > >>Thanks for your comment, onestone~ >> >> >>>Clean supplies are as important as stable ones. The internal 1.5V >>>reference would seem a better choice for you. then you can run on >>>batteries quite happily, use the internal power supply monitor to >> >>keep >> >>>tabs on the supply voltage and still get good A/D results as the >> >>battery >> >>>fades. >> >>The analog output is 0V-3V. So, using 1.5V internal reference is > > not > >>suitable I think... >> >> >>>get a better one. You also need to study the data sheet more >> >>closely. It >> >>>speciifes that no voltage applied to any pin should exceed Vcc by >> >>more >> >>>than 0.3V, and that this is a maximum rating. ie you shouldn't >> >>design it >> >>>with AVcc > Vcc. >> >>The device in fact is a electronic watch which uses a normal 2032 >>battery. So, I need try my best to minimize the power consumption. >>The low noise DC-DC convertor (TI TPS60243) is quite low in >>efficiency when the load is low. So, when the analog sensing part > > is > >>off (most of the time), the watch is used as a normal clock. A >>minimal current is needed (e.g. <20 uA) at normal clock but it > > cannot > >>be satisfied using this convertor. So, I prefer to use the battery >>directly as DVCC. Of course, I don't want to use too expensive DC- > > DC > >>convertor. >> >>Datasheet said that ADC input can accept upto AVCC+0.3V. I just > > think > >>that if we keep the AVCC at 3V even the DVCC is only 2.7V, my > > circuit > >>can still accept the 0-3V analog ADC data accurately. >> >> >>>If you look at the specs for the MSP430Fxxx you will see that the >>>minimum voltage for flash programming is 2.7V. personally I would >>>recommend a minimum of 3.0V. Get another Dc/Dc converter. there > > are > >>>hundreds of different types out there, some rated up to 1A in > > tiny > >>>packages. Most of these are very efficient. >>>You can supply AVcc < DVcc but not the other way round. >>> > > > > > . > > > > ">http://docs.yahoo.com/info/terms/ > > >