Ultra low quiescent current gate driver IC - Page 1
Forum section: electronics / projects

author: Manul
author_rank: Super Contributor
timestamp: February 22, 2021, 09:26:46 pm
content: I was looking low side gate driver IC's and sadly the quiescent current is not loudly advertised, so it is a long search through datasheets. What I found is the TPS2828 and TPS2829. The supply current typical 100nA. What I do not like is that maximum is 15uA. Overwise these ICs look ideal for the job. Input current is also nice - 200nA.Do you know any competitors for TPS2828?Quiescent current < 1uA (5uA absolute maximum)Input current < 1uASupply range approx. 5-15VDrive current >100mA

author: Limhes
author_rank: Contributor
timestamp: February 23, 2021, 06:20:51 am
content: Do you really need an IC or could you go discrete? Because there's low leakage MOSFETs around with which you could build your own low quiescent current gate driver.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 23, 2021, 07:32:35 am
content: Don't know of any offhand.I have noticed most use a common-source NMOS input stage, with pull-up bias, presumably to set input threshold and hysteresis (hence TTL input levels on a 18V+ device). This probably accounts for the majority of the ~0.3mA supply consumption they draw.Heh, TPS2828 must be pretty old, datasheet says 1997 at least, looks to be classic BiCMOS. Funny, I remember seeing Fairchild seemingly trademark a "MillerDrive" of very similar design. Would be rather ridiculous for such an obvious method to be novel.Something else to consider: intermediate input levels, and switching loss (typically given as equivalent node capacitance or something like that). The schmitt trigger input stage draws quite a lot of bias current for intermediate voltages, you want to switch it quickly (say from other CMOS logic) to keep supply current down. Illustration,https://www.ti.com/lit/an/scea046/scea046.pdf?ts=1614038564769And the switching loss, you're simply stuck with. The best you can do is use a smaller gate, perhaps 5-6x CD4069UBE in parallel (one less than the full chip in case you need noninverting, put the extra out in front) which gets in the ballpark of a 40 ohm output resistance, good enough for your requirement -- albeit at say 9V+, not down at 5V.74HC or LVC will do quite nicely at low voltages; you'll have a harder time covering all of them (5-15V contiguous) at once.And of course a BJT emitter follower (complementary pair, class C / unbiased) can boost a single CD4000 gate to those levels, without adding supply current; at some expense to saturation voltage (~0.7V in from each rail), which isn't great at low voltages, or for logic-level FETs.For exactly this sort of situation, I have made a low power drive circuit, which manages something like 50uA supply current for ~200ns edges into, what was that, around 60nC total gate charge I think? Not terrifically fast, like 10mA peak, but my concern was more, getting anything at all, than doing it absolutely perfectly.Tim

author: Manul
author_rank: Super Contributor
timestamp: February 23, 2021, 02:42:59 pm
content: Thanks all,Short shoot-through and gate charge is not a problem, because the duty cycle will be extremely low. I calculated that and it all fits well. What I don't want is the circuit to just waste power when it is idle, because idle time is very long and quiescent current becomes dominant. I guess I need to change my mindset and go discrete. I will do simulation with bjt complementary pair, feels like it should do the job, thanks Tim!Generally I avoid going discrete, because it is easier and less messy to take a fully characterized building block. But, man, so much drivers are wasting like milliamps of quiescent! I never noticed that before, but now when I need low quiescent I realize it is a hole in the market.

author: KT88
author_rank: Frequent Contributor
timestamp: February 23, 2021, 10:05:37 pm
content: Could you specify your in- and output voltage as well as (load-) current? In some cases it is possible to 'abuse' ICs that were designed for other puposes.I don't want to start guessing here...CheersAndreas

author: Manul
author_rank: Super Contributor
timestamp: February 23, 2021, 10:42:03 pm
content: For output I need >100mA current to get enough speed and around 10-12V supply.For the input it depends. I'm still juggling ideas. Idealy I would like it to accept supply range levels, let say 0-12V, but other levels might be adapted.If you mean to use comparator, I was not able to find fast enough comparator with low supply current.

author: KT88
author_rank: Frequent Contributor
timestamp: February 23, 2021, 11:44:20 pm
content: This looks like something to start with:https://www.analog.com/en/products/lt8494.html7uA operating, 300nA in sleep...Maybe to large, maybe too expensive - not much fun to build it yourself....

author: Manul
author_rank: Super Contributor
timestamp: February 23, 2021, 11:59:56 pm
content: Quote from: KT88 on February 23, 2021, 11:44:20 pmDo you suggest to somehow use this as a mosfet gate driver? As I understand these can only sink current, no? I mean, the SW is just an open drain.

author: KT88
author_rank: Frequent Contributor
timestamp: February 24, 2021, 12:06:11 am
content: ...it sounded like a boost regulator application...Some more application background would help...

author: Manul
author_rank: Super Contributor
timestamp: February 24, 2021, 12:24:44 am
content: Thank you, KT88, maybe some things were not clear, sorry. Basically, what I'm doing is a fast, floating solid state relay. It is part of bigger project. It does not need to switch often, just fast and has really limited supply current, so I started thinking how to minimise the quiescent current of gate drive.

author: uer166
author_rank: Super Contributor
timestamp: February 24, 2021, 01:03:54 am
content: Why not a normal, fast gate driver (whatever you need), and a FET or HSD upstream to disconnect it from power when not in use?

author: Manul
author_rank: Super Contributor
timestamp: February 24, 2021, 01:41:36 am
content: Quote from: uer166 on February 24, 2021, 01:03:54 amWell, I'm sure it is possible to some extent. But how I would drive that power switch FET? If driver IC uses decoupling capacitance, it will not start quick, or if it is without decoupling the power switch needs to be low Rdson and so it comes back to the same problem of driving FET.

author: Manul
author_rank: Super Contributor
timestamp: February 24, 2021, 02:15:52 am
content: I also found ZXGD3005E6 which has 50nA max quiescent, except that it has current driven input. Strange IC. Still interested if someone knows a modern alternative to TPS2828. Actually I will order that one for next week to test in practice and also I will try discrete driver.It is sad that parametric search is not giving quiescent current for these drivers. Damn, life would be easier.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 24, 2021, 06:03:43 am
content: Quote from: Manul on February 24, 2021, 02:15:52 amHah... compare to this one,https://www.diodes.com/assets/Datasheets/ZXTC2045E6.pdfor any other dual BJT. See the similarities?They're trying to specify it as a gate driver, to avoid having to specify it as a BJT... but it's still a BJT and they can only do a bad job hiding that fact.Tim

author: magic
author_rank: Super Contributor
timestamp: February 24, 2021, 08:12:31 am
content: Quote from: Manul on February 23, 2021, 10:42:03 pmIf the control signal is already rail to rail, a complementary emitter follower seems like the easiest option.If it's not, perhaps find a logic level FET and then same as above.

author: Manul
author_rank: Super Contributor
timestamp: February 24, 2021, 01:56:41 pm
content: Quote from: T3sl4co1l on February 24, 2021, 06:03:43 amOh, so then it means ZXGD3005E6 input current is not static? It is a follower? If yes, then it is not a bad option, it has really high current gain.