From: David Van Horn <david.vanhorn@backcountryaccess.com>
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Date: Tue, 21 Apr 2020 08:57:40 -0700
Subject: Re: [EE] LDO reg keeps failing. Looking for suggestions.
Thread-Topic: [EE] LDO reg keeps failing. Looking for suggestions.
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The spinning motor will act as a generator when it's not being driven. and =
there are inductive transients to consider.   I'd want to see a scope trace=
 with voltage and current, but the fact that the regulator is dying is stro=
ng evidence that this is happening.

The reverse polarized diode across the regulator from output to input pins =
is easy, cheap, and never a bad idea.
________________________________
From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Isaac =
Marino Bavaresco <isaacbavaresco@gmail.com>
Sent: Tuesday, April 21, 2020 9:38 AM
To: piclist@mit.edu <piclist@mit.edu>
Subject: Re: [EE] LDO reg keeps failing. Looking for suggestions.

How could Vout raise without the regulator suplying the voltage? Are
there any other power sources to the MCU?


Em 20/04/2020 22:33, David Van Horn escreveu:
> I disagree.
> The failure mechanism is well documented, where Vout > Vin.
> The point of D8 is to prevent the input pin from being more than a diode =
drop below Vout in that situation.
> But the problem mechanism here isn't Vin falling, it's Vout rising.
> ________________________________
> From: piclist-bounces@mit.edu <piclist-bounces@mit.edu> on behalf of Isaa=
c Marino Bavaresco <isaacbavaresco@gmail.com>
> Sent: Monday, April 20, 2020 7:12 PM
> To: piclist@mit.edu <piclist@mit.edu>
> Subject: Re: [EE] LDO reg keeps failing. Looking for suggestions.
>
> I think D8 is not necessary and may be detrimental in case of reverse
> polarity connection.
>
> If added, D8's cathode should be connected to where D9's  cathode is. As
> you added D9, D8 is not necessary.
>
> That configuration used to be suggested in older regulators datasheets
> for application where Vin could fall too quickly as result of a sudden
> current sink from other circuits, then current would backflow from the
> output capacitor to the input pin. With D9 present, that not possible,
> the only path to discharge C1 is through the regulator itself.
>
> Cheers,
>
> Isaac
>
>
>
>
> Em 20/04/2020 21:56, James Burkart escreveu:
>> Thanks for the info, everyone!
>>
>> So I added a 4.7uF cap to the output of the reg, added a shunt schottky
>> diode across the regulator, and another schottky diode feeding the input
>> filter cap.
>>
>> How does that look?
>>
>> --
>> Sincerely,
>>
>> James Burkart
>> *925.667.7175*
>>
>> [image: image.png]
>>
>
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