Adafruit Servo-HAT: P-Channel MosFet issue

[rubencc]

Hello,
I bought the Adafruit servo HAT, but unfortunately there was an issue with the regulator chip just next to the DC Jack when I first tested the board. (red arrow on picture) I soldered the headers on the board and could communicate with it. (HAT was visible on the Raspberry Pi on the correct standard address) Afterwards I plugged in the external 5V supply on the DC Jack, after which the green LED on the board went on, but the regulator chip started smoking as well. (little packaging burns on top of the chip visible) I quickly disconnected the supply to prevent further damage. You can see a picture of the voltage measurement of the external supply in attachments. The HAT seems to work properly since communication was not an issue and the green LED functions, however the regulator chip is defective. How to proceed with warranty?

Best regards,
Ruben

Reference: HAT-PWM-SERVO
Order Reference 50806 - placed on 12/03/2024

[Dominique]

Hi,
It is not a regulator but a P-Channel MosFet (ref: AOD417) designed as a Sacrificial component to protect the remaining of the board against reverse polarity. The reference can be readed on the component.
The Mosfet is strong component, so it has been exposed to out-of-range usage condition.
This has been cause by human error.

This component can be replaced or you can by-passed the protection Mosfet (see image attached).
In case of by-passing the next polarity (or voltage error) will burn the remaining of the board (and possibly the Pi).

Cheers,
Dominique

[rubencc]

Hi,

Could you explain me how I could have created an out-of-range usage condition?
From what I understand from the datasheet of the P-Channel MosFet, the component should be able to protect to an inverse polarity of 30 V.
This wouldn't be possible with the 5V supply even if it was inverted, since this is the purpose of this Mosfet as I understand?

Best regards,
Ruben

[Dominique]

Hi,

1) First word you have use for that component was "regulator". Meaning you expect it to regulate the voltage down to 5V.
Change are that voltage applied was higher than 5V.

2) The HAT have been designed for 5V, so spec was not to protect up to the Vds voltage (30 volts) but reverse 5V what it certainly does. Keeps in mind that typical value are not real value. Reality is always lower (read 30 think 20 to 25).

3) According to the 5V design, Vgs voltage must also be considered. Due to the low-voltage specs, there is no Zener Diode to protect Vgs against over-voltage (which is perfect in such cas)

Sélection_368.png (4.06 KiB) Viewed 3318 times

4) Another idea come to my mind: have you check for a short-circuit between 5V and GND on the Servo connector ? A very high current could create thermal issue on the MosFet.

Regards,
Dominique

[rubencc]

Hello,
I wrongly used the term regulator since I quickly googled the issue before posting to this forum and someone used this term. I did not look further in to it, since you would of course have all the details. However this doesn't mean I treated it like a regulator, since I showed you the supply voltage that I attached to it: the 5.16V as shown with the multimeter. So this shouldn't have created the issue. I also checked my servo connectors and there is no short-circuit.

I have the same issue as posted on the adafruit forum in the link below. Multiple people posted having the same issue and got their HAT replaced by adafruit, why is it in this case certainly a customer failure?
https://forums.adafruit.com/viewtopic.php?t=106367

[Dominique]

Hi,
The HAT is prototyping device (bare material). Such material is warranty for 15 days from the date of delivery against manufacture issue.
The board was sold in march 2024. Please understand that many month later, we are out of applicable warranty for such prototyping material (it would be the same at Adafruit).

Please, could you post a picture of the servo connectors soldered on the Hat?

Have you check the resistance between the GND and 5V rail on the Servo connector ?

> why is it in this case certainly a customer failure?

MosFet are beefy component. Adafruit have great supply chain (components are tested by manufacturer).
Each Adafruit board is tested before packing. I do myself use lot of Adafruit board from 9 years now.
I do also used and documented that board. So I do also know it.
Except if the component isn't an AOD417 (see labelling on the components), the two only possibilities are:
1) Improper supply condition
2) High current on the power circuit (raison why I'm asking you to measure the resistance between 5V & GND on the servo connectors).

Regards,
Dominique