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I'm trying to identify a burnt component on a PCB. This is receiver from Hubsan H301 RC glider. Wings got detached mid air and it slammed into high grass. I forgot to release throttle stick and prop got entangled in the grass. When I found glider there was a smoke coming from the plane. I quickly removed battery but damage was already done. As soon as battery is connected motor is spinning at full power and immediate smoke from the board is observed again. All other functions of the board work as before. Visual inspection revealed obvious damage to one component. See the picture below. This component controls power to the motor. To my surprise positive lead of the 2S battery supplying power to this board has direct connection to the motor. Second wire of the motor is connected to the common top row of the damaged component therefore it controls ground connection to the motor. Leftmost three leads in the bottom row of the 8 pin component are also connected together. As far as I can tell writing on the component is 330CSAD or 3300SAD. I think this is some mosfet similar to SIR330DP. http://www.vishay.com/docs/67089/sir330dp.pdf Is this true or did I get it completely wrong?

enter image description here

Picture of the board. Original is from http://images.amain.com/images/large/hub/hubh301f-07.jpg

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    \$\begingroup\$ It's probably a mosfet. \$\endgroup\$
    – Andy aka
    Dec 6, 2015 at 13:31
  • \$\begingroup\$ If you're certain it's connected like that... Based on the part number I would have guessed FDMC3300... which is a dual mosfet package. \$\endgroup\$
    – Fizz
    Dec 6, 2015 at 13:41
  • \$\begingroup\$ Yes, I'm pretty sure it's connected like that. I was using 20x magnifier to check. \$\endgroup\$
    – Farid83
    Dec 6, 2015 at 13:45
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    \$\begingroup\$ @RespawnedFluff I don't think so. It is clearly being used to PWM the brushed DC motor that turns the prop, along with the freewheeling diode visible closer to the connector. A dual N-channel would not make any sense there. \$\endgroup\$
    – jms
    Dec 6, 2015 at 13:46
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    \$\begingroup\$ @Farid83 - Are the common three connections connecting into GND (black battery wire)? If so it would tend to confirm that the FET is an N-Channel one and your data sheet guess is pretty close if not the correct part. \$\endgroup\$
    – Michael Karas
    Dec 6, 2015 at 13:49

1 Answer 1

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The broken component is a N-channel power MOSFET being used to control the motor current.

schematic

simulate this circuit – Schematic created using CircuitLab
The MOSFET was packaged in one of the propietary variants of the 8 pin SOIC, such as PowerPAK SO-8, P-TDSON8 or LFPAK power-SO8. It probably had a maximum drain to source voltage of 20 V or more, an on state resistance of 10 mΩ or less, and a continous current rating of 10 A or more. In order to save costs, it was likely being driven by a microcontroller directly instead of a proper gate driver, necessitating good performance at a low gate to source voltage. As such, the mosfet was probably of the "logic level" type, having a very low treshold voltage.

You do not have to find the exact same transitor that blew up. Find a power MOSFET in a compatible package which is sure to be electrically equivalent or better than the original. There are many suitable mosfets out there from different manufacturers and distributors. For example SIR158DP, BSC014N04LS, PHK31NQ03LT or AO4310 should all work just fine.

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    \$\begingroup\$ I confirmed it's driven by gate driver but my package guess turned wrong. Actually footprint is only 3mmx3mm and most likely a DFN package. \$\endgroup\$
    – Farid83
    Dec 12, 2015 at 11:46
  • \$\begingroup\$ @Farid83 Allright, it was hard to gauge the size from the picture, sorry for confusing things up. For reference, SO-8 is 4x5 mm in size. I thought that the 3-pin SOT package below the blown MOSFET was not driving the gate but was somehow related to the 3 pin header next to it. \$\endgroup\$
    – jms
    Dec 12, 2015 at 21:51

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