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I have this circuit schematic that shows a *2 behind the value for Cin and Cout. Does the designer mean two capacitors of that value in parallel on the input and output? Is that a common way of doing that? It looks very error prone to me. (full datasheet) enter image description here

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  • \$\begingroup\$ What datasheet for the device says? Oh, I see it says nothing, you took this pic from the datasheet. Lack of such info is the first sign to withhold using device until clarified by the device manufacturer. \$\endgroup\$ – Anonymous Jun 2 '17 at 12:24
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    \$\begingroup\$ That sounds to be the most logical explanation: two capacitors of that value in parallel. I have never seen it though in any other datasheet until now. \$\endgroup\$ – nickagian Jun 2 '17 at 12:26
  • \$\begingroup\$ Yes, the datasheet is lacking a whole lot of info. Does indeed give a bad impression about the part. \$\endgroup\$ – PTS Jun 2 '17 at 12:34
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It means you use 2 x 22 uF for the output i.e. two 22 uF caps in parallel and for the input you use 2 x 10 uF caps in parallel. It's not commonly used but I have seen it dozens of times at least.

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  • \$\begingroup\$ The sense of it? Backup capacitor if another fails? \$\endgroup\$ – Anonymous Jun 2 '17 at 12:42
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    \$\begingroup\$ It could be because two caps might be a less expensive way of getting the low value of ESR required. \$\endgroup\$ – Andy aka Jun 2 '17 at 12:45
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    \$\begingroup\$ That they recommend 2 without specifying a part or type is strange. \$\endgroup\$ – StainlessSteelRat Jun 2 '17 at 14:16
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    \$\begingroup\$ It's a poor data sheet. \$\endgroup\$ – Andy aka Jun 2 '17 at 14:17
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    \$\begingroup\$ Their application note is better, but surprisingly it does not reassure me. It would actually make me want to look at alternatives. \$\endgroup\$ – StainlessSteelRat Jun 2 '17 at 14:46
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In Design Consideration with AP3512E/3E, they discuss input and output capacitors.

They do not get into the x2 issue, but the recommended PCB layout shows x2 capacitors on input and output. Their only acknowledgement is big value and total capacitance.

Ultimately on input, although they discuss other types, they recommend a big value, high-quality X5R or X7R type dielectric ceramic capacitor

to filter noise at input voltage source and limit the input ripple voltage

and

better temperature and voltage characteristics

Output capacitor selection depends output ripple (total capacitance and ESR) and transient response. They recommend:

X5R or X7R ceramic dielectric capacitor, or other low ESR tantalum capacitor or aluminum electrolytic capacitor

Lots of design data and recommendations, that is missing in the data sheet, are in Application Note 1092.

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  • \$\begingroup\$ Good, thank you for the link. Now it is clear why the datasheet is poor. The device was developed by the Chinese company BCD Semiconductor Manufacturing Limited datasheetspdf.com/PDF/AP3512E/935208/1, and I am sure Chinese version of datasheet was pretty good. Then BCD was acquired by Diodes Inc with HQ in TX/US, but none cared to improve English datasheets, they just put their logo on it. This is a shame. \$\endgroup\$ – Anonymous Jun 2 '17 at 16:21
  • \$\begingroup\$ @Anonymous It also explains why the schematic is right to left. \$\endgroup\$ – StainlessSteelRat Jun 2 '17 at 17:08

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