BQ51050B: BQ51050B

Hello

Can you send schematics for review?

Also coil P/N or data sheet?

 The schematic shown along with the coil PN.

Hi 

Circuit looks OK.

A possible problem is the L value of the coil, 8uH is on the low side.  You will see problems with low gain, at higher output  voltage cannot deliver current.

As a test try higher L coil similar to Wurth 760308103215, 14.3uH and  48mm X 32mm.

What is the coil to coil distance?

Thanks for the information.  I will try increasing the inductance.  The distance is 4mm

I used the a 14uH coil from TDK with similar results.  Attached is the battery voltage plot.

the PN for the above test is: WR383245-17F5-G

I also tried another Wurth coil, PN:760308103205 with similar results.

The new coils look OK, thought they would have helped.

Just to double check you did re-tune C61, C65, C66.

WR383245-17F5-G -- 13.9uH -- total C about 165nF ( 13.9uH + 10%)

760308103205 -- 11uH -- total C about 210nF ( 11uH + 10%)

Couple of other things to check:

1.) Output current is set to 1.1A, unit could be hitting thermal limit. -- Does unit seem to be overheating and does reducing output current help?

2.) Comm caps are 47nF, should work but have you tried 68nF.  If Communications is a problem the higher value will help.

3.) Try increasing R-FOD to 235 or 250 ohms.  If FOD is a problem this will help.

A scope capture of RECT vs OUT when unit is dropping out will help.