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We use your CS8182 LDO, which has a note on page 7 warning the user that the ESR of the output cap is important to have within some unspecified range for stability. We have an application using them where they have 15Vin and produce 5Vout, at about 20mA, with intent of a 10uF ceramic bypass and a 0.1uF ceramic bypass on that output. ON Semi makes a similar part with nearly identical datasheet, the NCV8184, that has identical wording on its page 7, but goes on to add a paragraph saying one should look into an App note on your website called "Compensation for Linear Regulators" doc # SR003AN/D ... I have tried all sorts of things and can not find that doc on your site. Further, the NCV8184 does give the user stability plots on its page 3 (Figs 4-5) which would be great, except you will notice that Fig 5 claims for C2=0.1uF the Unstable region is below the line and on Fig 4 it claims that C2=0.1uF is stable below the line ... that is, for ESR=1 Ohm and C2=0.1uF, Fig 4 says you would be stable for all loads and then Fig 5 says you would be unstable for all loads ... I think ON Semi wants to rethink at least one of those plots. So we get back to my question on seeing suggested ranges of ESR for let's say 10uF at 5Vout and around 20mA for a CS8182 ... can you shed some light? Thanks
There is an unstable low ESR region for 0.1 uF only (and lower capacitor values). It is shown on figure 5 where the ESR of let say 1 Ohm would cause stability issue in case of 0.1 uF capacitor value. The 1 uF capacitor (and higher values) does not exhibit low ESR requirement for stable operation, in other words there is possible to use ultra low ESR 1 uF (or higher value) capacitor (e.g. ceramic) to achieve stable operation of the tracker. The higher ESR limit depicted on Figure 4 shows that ESR of 6 Ohm would also cause stability issue for 0.1 uF while with 10 uF capacitor and 6 Ohm ESR the tracker would operate stable. As there is not used logarithmic axis scaling these ESR charts has been just split into the two different charts showing the low and high ESR limits separately.
Regarding CS8182:
I recommend using 22 uF ceramic capacitor with (0.33 Ohm) additional series resistor to emulate ESR of capacitor to achieve stable operation over full output current, input voltage and temperature range. This would be the most stable solution.
The 10 uF capacitor would require 0.6 Ohm ESR for stable operation at 20 mA of an output current
Answered by: ON Semiconductor
2013-02-25 08:11:06.359