Motor Driver IC Blown up. Wish to know what went wrong

I am using 11.1V 25C 3700mAh Lipo Battery for powering up Motor driver Card (Dual DC Motor Driver 20A) Motor driver Product Link: http://robokits.co.in/motor-drives/dual-dc-motor-driver-20a .

Basically, I tried connecting two motors instead of single Motor on each motor port on the driver. So in all 4 DC motors connected as the motors had no load. As per my calculations, all 4 DC motors together cannot draw more than 4 Amps of current. DC Motor Specifications 10 RPM High Torque Dc Motor.

Link : http://robokits.co.in/motors/high-torque-dc-geared-motor-10rpm?cPath=2_3&

During this check I noticed that one of the IC LR 7843 on the motor Driver Card got burnt, the moment I powered it up with LiPo Battery.

Really don't Know why this happened.... Can someone please help me....

Can you take a picture of the board a little clearer? The back side too. I am curious as to what kind of drive circuitry they use and what fets are on the back. Those two little caps don't look they will help much to filter out a large power spike.

How do you mean you plugged in two motors per side? In series or parallel? And why?

To troubleshoot we would really need lots more info, schematic, board layout, and wiring to arduino and code.

Gather as much info as you can and we can help you more. We love pictures and schematics!

How long are your battery cables to the driver out of curiosity?

What is the stall or "locked rotor" current? Can you measure the motor resistance with an Ohm meter?

Those motors are described as "load current upto 7.5A" - which suggests you are completely wrong to make this statement:

As per my calculations, all 4 DC motors together cannot draw more than 4 Amps of current

As they can (and will at startup) draw a collective 30A. And maybe more if "load current" is less than stall current.

Ok so the timing of when it burnt out here matters, The OP said the MOSFET burnt the moment it was powered up ( the board ? or the moment the motors started trying to turn? ) .

They are quite heavy duty fets. Even if they were driving 30 amps continuous it would take a couple seconds before they melt down (dissipating 5 watts heat).

The voltage spikes when plugging in the battery can be many times more than the battery voltage. These fets are rated for 30 volts. I am willing to bet when you plug in your lipo (12.6v charged) they will see a spike up to 40-50 volts.

https://www.pololu.com/docs/pdf/0J16/destructive_LC_voltage_spikes.pdf

I am always curious as to why things fail. I hope the OP is still around.