Hi Doctormord, hopefully you will get answers. Datasheets never have everything that you wish for. Sometimes we have to do measurements ourselves. I apologize for not clearly stating that the Cstart info I provided was extrapolation based on my own board measurements. I got a bit excited when I saw that output common mode moved with Cstart, and I saw Cstart move with PVDD. Still haven't figured out exactly how they are doing that. I will stop guessing from now on!
I don't see a problem here, as long at the comparators reference voltage on the other input remains the same.
I actually figured out I was wrong about Cstart from these measurements:
1. At PVDD=24V, Cstart voltage was 2.38V. At 36V Cstart was 2.98V. So it definitely moves with PVDD.
2. Monitoring Vin on channel A I noticed Vin did not move: Vin stays 3.9V constant at both 24V and 36V. So it's not following Cstart directly, therefore Cstart is not the VCM.
3. Moving Cstart externally with a supply through a 10K resistor: It lowers Vout DC from 18V to 9V as you pull Cstart down from 3V to 1.5V.
TI has responded about the question of PSRR and Cstart - increasing does improve PSRR and even better in SE mode.
PSRR is 60dB with Cstart=10nF in BTL mode. It can be increased to 80dB by increasing Cstart to 100nF. In SE mode, Cstart is 1uF, so PSRR is helped. No plots are available, but PSRR is quite flat with frequency up to at least 10KHz.
TPA3251D2 - Audio Amplifiers Forum - Audio Amplifiers - TI E2E Community
PSRR is 60dB with Cstart=10nF in BTL mode. It can be increased to 80dB by increasing Cstart to 100nF. In SE mode, Cstart is 1uF, so PSRR is helped. No plots are available, but PSRR is quite flat with frequency up to at least 10KHz.
TPA3251D2 - Audio Amplifiers Forum - Audio Amplifiers - TI E2E Community
Well then nobody reads the datasheet, to see that either the block diagram or the answer is wrong. To me, having a bigger value for Cstart in SE mode is due to the output coupling caps. (to not have a loud ompf while powering up)
We might know better when the EVM is out.
We might know better when the EVM is out.
That totally makes sense as the voltage at this pin controls VOUTx, as seen in the datasheet. So a "misuse" of this feature would/could be output volume attenuation. 🙂 Nothing related to PSRR here. 😉
I know, I noticed that. I've bought from TI before and the service is quite excellent. I hope they get some back in stock soon. Digikey and Mouser both have lead times in the order of months. I hope TI prioritise their own internal stock first!
TI too? seems a lot of OEMs are enabling buying small quantities from their websites AFAIK Coilcraft was the leader in that movement, On Semi wasn't too far behind. In fact I don't think you can get them from the regular channels anymore at least in NA.
I'll really miss TI's easy order sample program. I reckon you can talk a local distributor/reps into still handing out some if you tell them a cool story. unless that's their goal cutting out the middlemen, then the reps will give you an earful on the phone LOL
I'll really miss TI's easy order sample program. I reckon you can talk a local distributor/reps into still handing out some if you tell them a cool story. unless that's their goal cutting out the middlemen, then the reps will give you an earful on the phone LOL
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I got my 5 samples in less than a week.
Layout a board this weekend.
Just can't make up my mind what configuration to use...maybe all.
well these G jobs , TI sent me an email informing me to re-register and bring a dot com email address.
what are you doing for a power supply?
In my stash I found a lil XFMR 500VA with dual 25V windings and +/- 10% taps on the primary. a couple of 25A bridges and dual 33,000uF i'll be in chip amp PS heaven. switchers are for losers, ill have 5 times your current and better eff.
custom XFMR sampled from one of my old jobs
what are you doing for a power supply?
In my stash I found a lil XFMR 500VA with dual 25V windings and +/- 10% taps on the primary. a couple of 25A bridges and dual 33,000uF i'll be in chip amp PS heaven. switchers are for losers, ill have 5 times your current and better eff.
custom XFMR sampled from one of my old jobs
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TI recently changed their policies such that you need academic or company email addresses in order to request free samples. If you do not posses one of these then you are allowed to buy samples from TI.
They may have gone one step further than this since though and now perhaps require all email addresses at a .com.
There are plenty of people out there who do abuse the free sample programmes that many of the chip manufacturers provide, so I can see why they've done this. I certainly do not mind providing the service exists and is affordable. With TI there is no minimum order, the prices are competitive and the postage is reasonable. I am glad they moved in this direction rather than simply stopping the programme altogether though.
They may have gone one step further than this since though and now perhaps require all email addresses at a .com.
There are plenty of people out there who do abuse the free sample programmes that many of the chip manufacturers provide, so I can see why they've done this. I certainly do not mind providing the service exists and is affordable. With TI there is no minimum order, the prices are competitive and the postage is reasonable. I am glad they moved in this direction rather than simply stopping the programme altogether though.
yes I reckon they'd consider a dot gov too. just weeding out the yahoos ( and Gmails ) so to speak.
there are other ways too...on a good day , you can hit up the reps for a handout, they like to talk.
there are other ways too...on a good day , you can hit up the reps for a handout, they like to talk.
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big iron and pure copper baby, in a few years most of you can only have dreams bout the good ol' days. heck it's getting harder to buy real copper hook up wire. As long as the outside is shiny and new you youngsters are fine hehe
yeah that and the folks that have to have a cool new iphone and shiny new hip car every two years... they say what about the environment...
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