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SDG #066 MLCC Capacitors Values Not What You Think! Tests with JLCPCB

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Language: en

00:00:00.290
hi in this video we're going to be
00:00:02.600 00:00:02.610 taking a look at ceramic capacitors and
00:00:04.700 00:00:04.710 why once you've deployed them in your
00:00:06.440 00:00:06.450 circuit the capacitance value of those
00:00:09.020 00:00:09.030 capacitors might not be what was
00:00:10.669 00:00:10.679 specified in the datasheet so this might
00:00:13.400 00:00:13.410 be already common knowledge to some of
00:00:15.289 00:00:15.299 you and obviously some of you may have
00:00:16.970 00:00:16.980 never come across this phenomenon but
00:00:18.740 00:00:18.750 basically what happens is once you've
00:00:20.810 00:00:20.820 applied a DC voltage to a Class two
00:00:23.120 00:00:23.130 ceramic capacitor the capacitance value
00:00:25.790 00:00:25.800 will be less than what was originally
00:00:27.109 00:00:27.119 specified in the datasheet so this is
00:00:30.080 00:00:30.090 particularly class 2 capacitors so
00:00:32.479 00:00:32.489 things like x7r y5e those type of
00:00:35.840 00:00:35.850 dielectric material ceramic capacitors
00:00:38.180 00:00:38.190 and what I've done is I've built up a
00:00:40.520 00:00:40.530 little circuit so that we can have a
00:00:42.049 00:00:42.059 look at the effect and how different
00:00:43.970 00:00:43.980 ceramic capacitors are affected in a
00:00:46.430 00:00:46.440 different way right so here's a
00:00:48.950 00:00:48.960 schematic for what I've implemented on
00:00:50.660 00:00:50.670 the PCB and basically we've got an RC
00:00:52.910 00:00:52.920 oscillator based around an op-amp so we
00:00:56.810 00:00:56.820 set our reference voltage 0.7 volts with
00:00:59.090 00:00:59.100 this diode here and then we've got an
00:01:01.220 00:01:01.230 op-amp setup as a comparator and as the
00:01:04.670 00:01:04.680 output increases to 5 volts then we
00:01:06.500 00:01:06.510 start charging the capacitor and then
00:01:08.660 00:01:08.670 once we reach a threshold then we set
00:01:10.820 00:01:10.830 the output to zero volts and that starts
00:01:13.070 00:01:13.080 discharging the capacitor so we see a
00:01:14.719 00:01:14.729 waveform of charging and discharging the
00:01:16.910 00:01:16.920 capacitor and the output looks like a
00:01:19.310 00:01:19.320 square wave pulse train then we've got a
00:01:22.910 00:01:22.920 little bit of circuitry here which gives
00:01:24.350 00:01:24.360 us a sawtooth and then a filter here
00:01:27.830 00:01:27.840 which gives us an output that's
00:01:29.030 00:01:29.040 proportional to the oscillation
00:01:30.740 00:01:30.750 frequency and that's what I've
00:01:32.480 00:01:32.490 implemented on this PCB and this PCB is
00:01:35.719 00:01:35.729 one made by a jail C PCB and this is the
00:01:38.870 00:01:38.880 first red PCB that I've had made and
00:01:40.880 00:01:40.890 actually the solder mask gives really
00:01:42.859 00:01:42.869 good coverage on this particular board
00:01:44.569 00:01:44.579 but yeah here's our bias voltage that we
00:01:46.999 00:01:47.009 apply here these are active pastors
00:01:49.340 00:01:49.350 under test obviously we only test one at
00:01:51.230 00:01:51.240 a time but I laid out a few different
00:01:52.819 00:01:52.829 footprints and then here's our DC output
00:01:55.550 00:01:55.560 which gives the proportional voltage
00:01:57.520 00:01:57.530 based on what the capacitance value is
00:02:01.090 00:02:01.100 all right so here's our circuit all
00:02:03.139 00:02:03.149 connected open what we want to do is
00:02:04.550 00:02:04.560 tweak the potentiometer so it reads one
00:02:06.649 00:02:06.659 ball exactly and so with zero bias we're
00:02:11.180 00:02:11.190 reading a value of one so that means our
00:02:13.010 00:02:13.020 term doesn't win
00:02:13.790 00:02:13.800 nanofied caster is at 220 nanofarads now
00:02:18.320 00:02:18.330 if we increase the bias to 5 volts you
00:02:22.180 00:02:22.190 can see that this has now dropped to
00:02:24.710 00:02:24.720 about 0.7 4 volts so that means our 220
00:02:29.750 00:02:29.760 nanofied capacitor is now 162 nano cards
00:02:35.840 00:02:35.850 and if we increase that to 10 volts its
00:02:43.540 00:02:43.550 0.45 so 220 times 0.45 we're at 99 nano
00:02:49.340 00:02:49.350 farad's and if we do it up to its
00:02:51.410 00:02:51.420 maximum work in voltage of 16 volts
00:02:59.380 00:02:59.390 we're at 0.3 so to 20 times 0.3 out of
00:03:05.090 00:03:05.100 220 nano farad capacitor is now only 66
00:03:08.210 00:03:08.220 nanofarads so you can see that if you
00:03:10.550 00:03:10.560 were to use this in your circuit and you
00:03:12.200 00:03:12.210 were relying on that value specifically
00:03:14.590 00:03:14.600 then it wouldn't be behaving exactly as
00:03:18.199 00:03:18.209 you intended so what I've done is I've
00:03:20.570 00:03:20.580 tested a whole range of different
00:03:21.770 00:03:21.780 capacitors and then logged all of the
00:03:24.050 00:03:24.060 whistles first of all we've got the y 5v
00:03:27.160 00:03:27.170 dielectric capacitors they're all 50
00:03:29.420 00:03:29.430 volt 100 nano farad capacitors the only
00:03:32.480 00:03:32.490 difference here is the case sizes but
00:03:34.820 00:03:34.830 you can see here they all start off at
00:03:36.230 00:03:36.240 their specified capacitance but by the
00:03:38.660 00:03:38.670 time they've reached their maximum
00:03:39.860 00:03:39.870 working voltage they're only at 20% of
00:03:42.410 00:03:42.420 their original capacitance value and one
00:03:44.810 00:03:44.820 thing that you can note here is that the
00:03:46.310 00:03:46.320 larger 12:06
00:03:47.540 00:03:47.550 capacitor does drop very slightly less
00:03:50.210 00:03:50.220 rapidly than the smaller o 6:03
00:03:53.000 00:03:53.010 capacitor and then we've got the x7r
00:03:56.090 00:03:56.100 dielectric capacitors and I've tested a
00:03:58.070 00:03:58.080 few parameters here so different case
00:04:00.260 00:04:00.270 sizes different working voltages and
00:04:02.540 00:04:02.550 then different capacitance values so
00:04:04.760 00:04:04.770 these were all 100 nanofarads except for
00:04:07.520 00:04:07.530 these two 1 micro farad capacitors and
00:04:09.500 00:04:09.510 these both declined more rapidly than
00:04:12.650 00:04:12.660 the lower capacitance capacitors and
00:04:15.550 00:04:15.560 also the lower working voltage pasteur
00:04:18.680 00:04:18.690 declined more rapidly than the high
00:04:20.390 00:04:20.400 working voltage and that's illustrated
00:04:22.790 00:04:22.800 more promptly here by the 200 volt
00:04:25.219 00:04:25.229 capacitor which is declining
00:04:26.360 00:04:26.370 significantly
00:04:27.590 00:04:27.600 than all of the others then we've got
00:04:30.110 00:04:30.120 basically the same story as before so as
00:04:32.150 00:04:32.160 the capacitor size physical dimensions
00:04:34.460 00:04:34.470 increase the decline in capacitance
00:04:37.340 00:04:37.350 value is slower and I did test that 200
00:04:40.640 00:04:40.650 volt capacitor all the way up to 150
00:04:43.220 00:04:43.230 volts which is about as much as I could
00:04:44.540 00:04:44.550 take it to and you can see it follows
00:04:46.700 00:04:46.710 exactly the same shape and it's sort of
00:04:48.920 00:04:48.930 asymptotes towards the same sort of
00:04:52.030 00:04:52.040 nominal value at the end of its working
00:04:54.260 00:04:54.270 voltage but if you did want to use your
00:04:56.810 00:04:56.820 capacitor at 50 volts it might make more
00:04:59.120 00:04:59.130 sense to use a 200 volt capacitor as
00:05:01.760 00:05:01.770 opposed to something rated at 50 volts
00:05:04.870 00:05:04.880 and then just for completeness I also
00:05:07.760 00:05:07.770 tested a few different technologies of
00:05:09.710 00:05:09.720 capacitors so I've kept on this graph
00:05:11.780 00:05:11.790 one of the y5v capacitors that's this
00:05:14.210 00:05:14.220 one with the steepest slope then we've
00:05:16.460 00:05:16.470 got the x7r they've got an electrolytic
00:05:18.920 00:05:18.930 in orange here and that actually
00:05:20.480 00:05:20.490 increased in capacitance with voltage
00:05:22.790 00:05:22.800 and then we've got three overlapping
00:05:25.040 00:05:25.050 lines here which are very stable across
00:05:27.320 00:05:27.330 the band and that is the class one
00:05:29.360 00:05:29.370 ceramics or a C 0 G or an MP 0 ceramic
00:05:32.660 00:05:32.670 capacitor those are excellent but
00:05:34.640 00:05:34.650 they're generally not available in
00:05:35.840 00:05:35.850 higher capacitance values then we've got
00:05:38.330 00:05:38.340 a Weiner MKS 2 metalized polyester
00:05:40.580 00:05:40.590 capacitor and was very stable and then
00:05:43.760 00:05:43.770 we've got a Panasonic polyester
00:05:46.100 00:05:46.110 capacitor and that Panasonic one was
00:05:48.650 00:05:48.660 stable right up until its highest
00:05:50.540 00:05:50.550 voltages here so at 100 volts it had
00:05:53.720 00:05:53.730 just started to tail off there but the
00:05:55.550 00:05:55.560 the wiemer MKS 2 was stable all the way
00:05:58.280 00:05:58.290 up to its maximum working voltage so
00:06:01.520 00:06:01.530 what is it about the ceramic capacitors
00:06:03.350 00:06:03.360 that causes the capacitance to decrease
00:06:06.290 00:06:06.300 with DC bias applied to the capacitor
00:06:09.050 00:06:09.060 plates
00:06:09.530 00:06:09.540 well the dielectric material within
00:06:11.360 00:06:11.370 ml/cc capacitors is derived from barium
00:06:13.760 00:06:13.770 titanate and as the voltage on these
00:06:16.010 00:06:16.020 plates has increased the molecular shape
00:06:18.470 00:06:18.480 of the barium titanate molecule shifts
00:06:20.510 00:06:20.520 resulting in a clarity of the dipoles in
00:06:23.030 00:06:23.040 the capacitor structure so with no DC
00:06:25.580 00:06:25.590 bias on these plates
00:06:26.960 00:06:26.970 all of these dipoles are free to rotate
00:06:29.450 00:06:29.460 and that gives us the highest
00:06:31.990 00:06:32.000 capacitance because the dielectric
00:06:33.950 00:06:33.960 constant is a is maximum once we apply a
00:06:37.610 00:06:37.620 DC bias to these plates some of the
00:06:40.460 00:06:40.470 dipoles start
00:06:41.420 00:06:41.430 become locked in position and they're no
00:06:43.430 00:06:43.440 longer free to move that means that
00:06:45.920 00:06:45.930 we've got a lower dielectric constant
00:06:48.260 00:06:48.270 and therefore the capacitance is
00:06:49.790 00:06:49.800 decreased and as the DC bias voltage
00:06:52.969 00:06:52.979 increases more and more of these dipoles
00:06:54.980 00:06:54.990 start to lock in place resulting in a
00:06:57.560 00:06:57.570 lower capacitance this gives us some of
00:07:00.080 00:07:00.090 the reasoning behind why we end up with
00:07:01.790 00:07:01.800 these curves here so first of all for
00:07:04.550 00:07:04.560 the high-voltage capacitors like this
00:07:06.439 00:07:06.449 200 volt capacitor here the dielectric
00:07:08.840 00:07:08.850 material is much much thicker than on
00:07:10.969 00:07:10.979 the low voltage capacitors so what we
00:07:13.700 00:07:13.710 actually see is that the electric field
00:07:16.100 00:07:16.110 between the two plates is lower because
00:07:17.960 00:07:17.970 there's a greater distance and therefore
00:07:19.370 00:07:19.380 less dipoles are affected when the bias
00:07:22.370 00:07:22.380 voltage increases that's also a similar
00:07:25.430 00:07:25.440 effect to using smaller physical size
00:07:27.770 00:07:27.780 capacitors so when the physical size is
00:07:30.080 00:07:30.090 smaller for a given capacitance and
00:07:32.029 00:07:32.039 voltage the actual dielectric layers are
00:07:34.580 00:07:34.590 much thinner and therefore there's a
00:07:36.710 00:07:36.720 much higher electric field so the
00:07:38.300 00:07:38.310 dipoles become locked in place much
00:07:40.430 00:07:40.440 lower DC bias voltage and similarly for
00:07:44.120 00:07:44.130 the higher value capacitors so these 1
00:07:46.159 00:07:46.169 microfarad capacitors in order to fit
00:07:47.990 00:07:48.000 them into an Ohio v component size the
00:07:51.140 00:07:51.150 layers are way thinner than they are for
00:07:53.510 00:07:53.520 a 100 nano farad capacitor and therefore
00:07:56.270 00:07:56.280 the electric field is even greater in
00:07:57.920 00:07:57.930 those meaning that the dielectric
00:08:00.980 00:08:00.990 constant decreases much more rapidly as
00:08:04.040 00:08:04.050 a result of the DC bias across the two
00:08:06.020 00:08:06.030 plates so there's a few things that you
00:08:08.480 00:08:08.490 might want to consider when you're
00:08:09.500 00:08:09.510 designing your circuit the first is that
00:08:11.450 00:08:11.460 it may make more sense to use multiple
00:08:13.730 00:08:13.740 smaller value capacitors than one large
00:08:16.370 00:08:16.380 one because you'll be further up a slope
00:08:18.080 00:08:18.090 here with your multiple smaller values
00:08:21.080 00:08:21.090 in parallel the next is that you should
00:08:24.830 00:08:24.840 consider looking at using a higher
00:08:26.540 00:08:26.550 voltage capacitor where possible you
00:08:30.140 00:08:30.150 know so even if your circuit is
00:08:31.520 00:08:31.530 operating at 25 volts it may make more
00:08:34.040 00:08:34.050 sense to use a 200 volt capacitor and
00:08:36.500 00:08:36.510 just because it may get you further up
00:08:38.690 00:08:38.700 the curve and then finally potentially
00:08:42.380 00:08:42.390 the less desirable is that a physically
00:08:44.630 00:08:44.640 larger capacitor will hold its value
00:08:46.790 00:08:46.800 higher and a higher bias voltage the
00:08:50.690 00:08:50.700 downside to that is that very small
00:08:53.690 00:08:53.700 ceramic capacitors are excellent for
00:08:55.850 00:08:55.860 decoupling because they have such a low
00:08:57.590 00:08:57.600 inductance so by moving to a higher and
00:09:00.850 00:09:00.860 physical size then the inductance will
00:09:04.010 00:09:04.020 be increased and therefore you may have
00:09:05.900 00:09:05.910 other effects but there's a few
00:09:07.430 00:09:07.440 trade-offs to be made there and I would
00:09:09.650 00:09:09.660 recommend that you potentially build up
00:09:11.240 00:09:11.250 a little circuit like this they don't
00:09:12.740 00:09:12.750 always publish the data in the data
00:09:15.170 00:09:15.180 sheets I think the manufacturer TDK do
00:09:18.530 00:09:18.540 have some very basic slopes in the
00:09:21.020 00:09:21.030 datasheet for the ceramic capacitors but
00:09:23.570 00:09:23.580 obviously they don't really want people
00:09:24.710 00:09:24.720 seeing that their capacitors not going
00:09:27.380 00:09:27.390 to perform as expected so if you design
00:09:29.930 00:09:29.940 a little board like this and then you
00:09:32.180 00:09:32.190 can quickly test different types of
00:09:33.950 00:09:33.960 capacitors and see what kind of result
00:09:35.540 00:09:35.550 they're going to have if your circuit is
00:09:37.340 00:09:37.350 that critical so this would be
00:09:39.320 00:09:39.330 particularly useful for things like
00:09:40.610 00:09:40.620 switch mode power suppliers where you're
00:09:42.260 00:09:42.270 really relying on the capacitance value
00:09:44.330 00:09:44.340 to keep your circuit stable and say you
00:09:47.120 00:09:47.130 might want to design something like this
00:09:48.410 00:09:48.420 and then give a few different types of
00:09:50.690 00:09:50.700 capacitor a test so I hope you found
00:09:53.030 00:09:53.040 that useful leaving a comments or
00:09:55.130 00:09:55.140 thoughts or your experiences down in the
00:09:57.020 00:09:57.030 comments down below but until next time
00:09:59.000 00:09:59.010 thanks for watching
00:10:03.630 00:10:03.640 you
00:10:13.820 00:10:13.830

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