The current rating of D4 on your Feather V2 board

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FRDM4236
 
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The current rating of D4 on your Feather V2 board

Post by FRDM4236 »

I recently bought your Feather V2 based on the new ESP32-PICO-V3-02. It's a very nice board.
I have a question and would like to ask. You have 2 LDO regulators on board, they can totally at least provide 1A as you stated, the 1A is from the VBUS through the reversing current blocking diode D4. The D4, MBR540 (I think it's misprinted on your schematic, it may be a MBR0540, SOD-123 package), is only rated at 0.5A in the datasheet. Will it be overheated in an application that requires 0.9A?

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Re: The current rating of D4 on your Feather V2 board

Post by dastels »

Exactly which Feather do you mean? What product ID?

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Re: The current rating of D4 on your Feather V2 board

Post by FRDM4236 »

Sorry, it's ESP32 Feather V2. ID: 5400

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dastels
 
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Re: The current rating of D4 on your Feather V2 board

Post by dastels »

According to the MBR540 datasheet at https://pdf1.alldatasheet.com/datasheet ... BR540.html, it's rated for an average forward current of 5A.

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Re: The current rating of D4 on your Feather V2 board

Post by FRDM4236 »

I don't believe it's a MBR540. Why would you need a 5A diode for an 1A circuit? The MBR540 will have 100uA-2mA reverse leakage current. If you disconnect the USB cable and plug in a 4V LiPo battery, the voltage on the VBUS pin will be 4V with a 100K load resistor (R12). If there is a LED connected to the VBUS, it will be lit. So it couldn't be a MBR540.
I believe it's a MBR0540. Please ask the person who designed the circuit to verify it.

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Re: The current rating of D4 on your Feather V2 board

Post by dastels »

You bet

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Re: The current rating of D4 on your Feather V2 board

Post by adafruit2 »

hiya, yes we've placed a MBR0540 or MBR0520 with low Vf and ultra low reverse leakage. we've used it on our boards with single regulators and it got recycled into this. while *technically* you could draw 1A continuously from both regulators, in reality the SOT23-5 package will start to struggle dissipating that much heat. we'll look at bumping it to a PMEG2020 next time we fabricate, but for now you can either draw 0.5A continuous or up to 1A with a 50% duty cycle.
if you need a ton of current, grab it from the USB or VBAT pins, they are 'direct connect' and you can get up to 1A without going through the regulator :)

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Re: The current rating of D4 on your Feather V2 board

Post by FRDM4236 »

Thanks for the reply.
The MBR0540 is a 0.5A diode with low leakge, it's not a bad choice. I saw some boards would even use a 0.35A diode.  I am afraid that if an electronic part works out specs, it could degrade rapidly as it's shown on some graphs of datasheets. 
With all due respect, I am not sure that the PMEG2020 is the best choice, it's a 2A diode with higher leakage.  If users don't have problems with the MSR0540 (0.5A), a 1A diode will only be better for them.  You already have a low leakage 1A diode (NSR0320) on your QtPy boards. That could be a good choice to replace the MBR0540. 

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