Electronics > Projects, Designs, and Technical Stuff
PSA: do not use the TPS61099 boost reg in your designs
jeremy:
Hi all,
Just reporting a rather poor experience I have had with a new boost regulator on the market. It works like a normal adjustable boost regulator in that there is a resistor divider to set the output voltage (you can also get fixed devices that have it internally). However, if the rise time on the power supply is too slow or there are glitches, it ignores the feedback loop and goes to maximum duty cycle mode and locks up. For example, using the TPS610995 (which is the only one in a DFN package), instead of boosting my 2.8V supply to 3.6V, it occasionally boosts it to a constant 5.7V on startup. The worst part is that I am using the exact supporting components from the datasheet, with the exact same layout as per the datasheet (well, as close as possible; they don't specify dimensions ;) ).
Although this part is designed to be connected directly to a battery (they even have a reference design for it!), I have reproduced this problem using the contact bounce of just putting a battery in a holder. I assume that the same thing would happen with a particularly bouncy mechanical switch.
I wouldn't be so bothered if it would at least fail safe, rather than failing to max duty cycle and boosting to a high enough voltage to kill everything...
More info on the TI forum here: https://e2e.ti.com/support/power-management/f/196/t/756614 if you search the forum, it seems I am not the only one who has discovered this problem. But no satisfactory solution seems to exist.
I have tried to work around it with a voltage supervisor on the EN pin, but there seems to be a related issue I have found today wherein if the output voltage is higher than the input voltage on startup (for example, output capacitors still charged) the same thing can happen.
If anyone has any ideas about how I could work around something like this, I'm all ears :-//
Thanks,
Jeremy
Siwastaja:
Thanks for warning.
Sounds like typical TI engineering. I use their power conversion/management ICs less and less - they are overcomplicated and have excess state space, and therefore tend to hit unwanted states - and a typical "wrong state" tends to mean: blow up everything.
In this case, looking at the TI E2E forum posts, it seems like an UVLO event is running some kind of special startup sequence, which blows everything up if happening more than once inside a small time window. The problem is, it's completely normal and unavoidable that UVLO events happen frequently, and it shouldn't cause erratic behavior.
These things are IC design equivalents of spaghetti code from a total beginner. If this was a software, a fix would be another overcomplicated "UVLO filter unit" which would reduce the number of issues, but increase complexity again. But ICs can't be updated.
Gibson486:
That sucks...I have always had good experiences with TI's power chips (not a boost though). That said, I had a horrible experience with their high power op amps...and it was related to the enable pin as well. I have always relied on Linear Tech for boost converter stuff. It can be pricey, but it usually always works.
SiliconWizard:
Damn, that's good to know. This IC looked interesting on paper.
Reading the datasheet, we can see it's got quite a few different modes of operation. Between the soft-start feature, the "down mode", "pass-through", bust mode and synchronous mode... eek, there's probably a lot of cases, depending on how Vin and Vout relate, to make it go bonkers. In your case, I'm guessing it's probably stuck cycling between two of those modes (or more) in an unexpected way. This IC looks like a bunch of good ideas gone bad.
Not sure what you can do to get something reliable, short of switching to another boost converter altogether. Maybe select one of the Linear boost converters that have a burst mode and very low quiescent current (although this one will be hard to beat). Never had any problem with them.
A zener diode at the output is probably a bit pointless. It may protect your circuit but with the common Zener voltages of 3.6V and 3.9V (off the top of my head), you are likely to be in the diode knee most of the time, wasting unnecessary current... and even if that protects your circuit, I'm not even sure this would get the IC out of this weird mode when it happens, so either way, your device would probably not work properly. Maybe adding a second voltage supervisor at the output with a threshold of say 4V (if 4V is still safe for your circuit), that would disable the boost converter when getting higher than this. But that may just get it into an infinite loop of starting and disabling... and it starts getting a bit much for just one converter. Sucks.
PartialDischarge:
Not saying the IC is perfect but I see some fault on your part for not assuring a stable Vin before enabling the converter. You mention connecting directly the battery, or that the same would happen with a switch, but that is not how you are suppose to turn on the converter, that is what the enable pin is for. This chip has true disconnect so the battery is supposed to be connected at all times and use the enable pin to discoonect.
First connect the Vin source, of course if the impendance is high an input capacitor helps, then enable the converter. I personally would use a resistive divider in the E pin.
I have designed circuits with chained switched converters, and needed to control the enable of each one, assuring that the output of the previous converter was stable.
Navigation
[0] Message Index
[#] Next page
Go to full version