hi ritesh,
have u checked the tx and rx pins are properly connected with ur board? if u have multimeter pls check the reset pin when u initiate the loading.. if possible check any voltage drops.. sometimes usb to uart go bad. i faced with usb to uart converter bf810.
. and i can give u another suggestion too.. i want u to check download again with ur desktop pc using the same usb to uart converter. i think this may clear ur doubt on driver..
thanks and regarda,
karthikkr