BQ51013B: Output Current Limited to 400mA

Hello

The schematic looks good.

Do not see any problem with the waveform.

If you are using a the Wurth 760308103202, 48mm X 32mm 12uH this should be a good coil.

Things that will keep unit from getting to max current:

1.) ILIM set to low -- Resistors look OK.  Check the voltage at ILIM, current limit starts at 1V.

2.) Thermal limit -- device is getting too hot and limiting current.  PCB looks good but check thermal rise of the device.

3.) The test TX is having problem -- What TX are you using? Check the input voltage, is it dropping? What is operating freq, does the freq get lower with load?

4.) FOD fault could limit current -- Does TX indicate an possible fault condition, flashing Red LED.

Bill

You say you don't see anything wrong with the waveforms but none of the example waveforms in the datasheet show a drop in the rectifier voltage, even at 1A load.

1)  I measured the voltage at the I_LIM pin and it is not close to 1V.  I started at 350mA and increased the load current to 443mA at which point the output shut off.

Blue = RECT, GREEN = OUT, RED = I_LIM, LIGHT BLUE = Load Current 1A/V

The voltage at I_LIM rises to about 448mV when OUT turns off, RECT is sagging down to 3V

I then changed R_FOD to 150ohm with R1 = 100.  Starting at 350mA load the output drops as before, however around 400mA the output begins to momentarily shut off.  I varied the load current above and below 400mA and then the output suddenly jumps back to 5V and is regulated.  At that point I could increase the load further to 550mA before the output completely shut off.  It appears that there is a problem with the dynamic rectifier control and adaptive communication limit.  I'm not able to get the device to switch between Iout < 300mA and Iout > 300mA operation, and it won't startup in the Iout + 50mA mode.  

2)  Measured case temperatures are < 45C

3)  I do not have a testing TX.  I am using two off the shelf Qi chargers

Anker PowerWave Pad - A2503

Harmily Qi - MC-02A

The circuit performs the same for both chargers.  The measured input voltage on the USB input stays constant at 5V.  The input power increases from 2.9W at 350mA output to 5W at 450mA output.  I am not able to measure the output frequency.

4)  Both chargers show a red LED when power is on but not connected to a Qi device, then turn blue when a connection is made and charging begins.  The LED on both chargers stay blue while the output of the BQ51013 turns off.

Thanks for checking my first set of suggestions.

1.) ILIM set to low -- Resistors look OK.  Check the voltage at ILIM, current limit starts at 1V. -- Stays below 1V and out of current limit

2.) Thermal limit -- device is getting too hot and limiting current.  PCB looks good but check thermal rise of the device. --- Device temp less than 45C

3.) The test TX is having problem -- What TX are you using? Check the input voltage, is it dropping? What is operating freq, does the freq get lower with load?  ---- Nothing to indicate the TX is a problem.

4.) FOD fault could limit current -- Does TX indicate an possible fault condition, flashing Red LED.--- No signs of FOD fault / power starving active.

Dynamic Rectifier control and Communications Current limit:

1.) Communications current limit --- can be turned OFF by pulling EN2 high.  The feature will limit the output current at the output regulator during communications time, does not change the RECT voltage operating point, see table 5 in data sheet.

2.) Dynamic Rectifier Control-- will change the target regulation point for RECT voltage as a function of output load. The transition points are determined as a percentage of current limit set point (ILIM), see table 1 in data sheet.  This feature will help with light load to high load transitions.  It cannot be disabled.  

What type of load are you using in your test?