Teensy 3.5 input power regulator (LDO)

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vagyver

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Hello!

I want to power a teensy 3.5 with a variable voltage of about 6-8.2V but i read that the "Vin" pin has to be "3.6 to 6.0 volts" (from the little piece of page -brochure- i had with the board when i bought them).

So, by reading this i can't do that. That what makes me use an extra 7805, which i don't want to.

Next, by following the schematics i can see that the LDO is a LP38691.
From the manual it seems that this LDO's input is "Wide Input Voltage Range (2.7 V to 10 V" and if i read the absolute maxing rating can be up to 12V.

So, what is the correct one?


Thank you in advance!!!
 
Upon reading the datasheet you've linked, I saw that this part has multiple package types and the one on Teensy is the smallest of the three (WSON with thermal pad, vs. SOT-223 and larger TO-252). Teensy, however has a little PCB "island" underneath the regulator that acts as a heatsink.

Using 6 to 8.2V is feasible, but you have to make sure you're not overheating the regulator.
Using a separate 7805 (with protection diode, see this Datasheet (PDF page 30, Figure 27)) before Teensy is a safe choice.
 
Thank you for your reply.

I tried it too!
No fire or smoke!!! so it proved that it can accept bigger voltage (than the 6 volts it says).


I will keep an eye of the overheating issue too
 
The 6 volt guidance is somewhat conservative, based on the assumption you will also use the 3.3V pin to power other circuitry using 250 mA (plus the ~70 mA Teensy 3.5 uses if you run everything to the max). Many people do connect power-hungry 3.3V boards like WIZ820io and ESP8266. If you do that *and* give Teensy 10 volts, the regulator will overheat. If you don't consume extra power, there is extra capacity to handle higher input voltage without overheating.

Unfortunately, the simple single numbers can't capture these subtle trade-offs, so we just use pretty conservative numbers on the pinout cards and other documentation.
 
Hi Paul!
Fortunately, i know what you are talking about and i am familiar with that and that's why I asked the reason it says up to 6V.

So, now i got the answer and sounds very logical to me.
And sounds also quite -indirectly- protective too, to some people that are not very familiar about calculating power dissipation such as P=(Vin-Vout) * I ).

Thank you for explaining!
 
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