BQ25186EVM: BQ25186EVM

Hello again, 

I have the BQ25186EVM mostly functioning the way I'd expect.

However, I am having trouble exiting SHIP mode.

I can get the EVM to nicely go into SHIP mode by holding the button for 5s then releasing it.

But, I cannot get it to exit SHIP mode by pressing the same button for 2sec (per the datasheet).

The only way it exits SHIP mode is my inserting VIN.

I have the registers programming correctly I believe.

I have the device set for powering when either VIN or VBAT are present

Ship Mode enabled

Pushbutton long press enables SHIP mode and the datasheet says SHIP mode can be exited bywaking the device 

with a TSMR button press OR an adapter insertion. As I said the adapter insertion works, the TSMR will not work.

Any advice will be appreciated.

Thanks,

Dan

Here are the registers.

Hi Dan,

Thanks for sharing the registers values. It looks like these readings were taken while VIN was still connected, and I don't see any issues with your configuration.

What is the battery voltage while in ship mode? If VBAT is below the battery undervoltage lockout threshold (BUVLO), the charger won't be able to wake up from a push button press.

It would be helpful to see a scope capture of VBAT, VSYS, and TS/MR while attempting to exit ship mode using the push button.

Best regards,

Alec

Hi Alec,

Here are some pics, yellow = VBAT, Blue = VSYS, Purple = TSMR

This first one is with just VBAT, no VIN.

This next one is a long PB to get into SHIP mode.

Next one, in SHIP mode and I start pressing the PB, Vsys seems to try to come back but fails

Last one, I re-insert VIN and VSYS comes back

Sure, of course there's a load.

Are you thinkning the load has to be disconnected to get the VSYS rail back ?

Dan

Hi Alec,

I have tried several things to solve the problem, but so far no luck.

The load is about 300ma when I try to wake from SHIP mode. (small DC motor is attached to the VSYS rail via a step-up power supply)

I installed a TPS22917EVM and tried upto 5600pF capacitance to change the ramp-up (inrush).

This did not work.

I tried disconnecting the load and yes the VSYS rail comes back from SHIP mode when I press the PB to wake it, 

but as soon as I reconnect the load, the VSYS rail collapses.

Can you tell me what is the max inrush the VSYS rail can withstand?

Changing the 500ma setting to 1000ma did not change the behavior.

Please provide any other advice you can, 

Thanks,

Dan

Hi Dan,

Thanks for following up.

BATOCP can be set as high as 3A and will trip very quickly.

How much capacitance is on SYS? Does the issue still occur when BATOCP is set to 3A?

It would be helpful if you could share a waveform capture and register dump after SYS falls when the load is connected to VSYS. If we see that the BAT_OCP_FAULT flag is set, we can confirm BATOCP is the root cause. Otherwise, I'd be interested to see whether VSYS is falling below the VSYS_SHORT threshold when the load is applied.

Best regards,

Alec

Hi Alec,

To answer your questions.

1) I tried to set BATOCP to 3A, but the largest number in the menu was 31250, very odd. I did try the setting just below that, it was 1500ma.

That did not work. I checked all the flags and I do not see one that indicates a problem.

2) I measured the capacitance as best I could, the capacitance on VSYS seems to be about 16uF

3) I sent you the picture previously that what happens to VSYS when I try to wake the system. There is no short. VSYS jumps to 2V quickly, oscillates a few cycles then gives up.

Here's the pic again. The blue trace is VSYS trying to turn on when I press the button. If I remove the load, VSYS does turn on and stay on. Clearly, the problem has something to do with the inrush. If I try to connect the load WITHOUT a VIN the VSYS rail crashes just like with the WAKE I described.

Hi Dan,

Thanks for following up.

The "31250" BATOCP setting in the TI Charger GUI is the 3A BATOCP setting. Thanks for pointing this out. We will correct it in the GUI. The typical threshold for the 3A BATOCP setting is 3.125A. Does the issue still occur with this setting?

If the issue still occurs, I recommend incrementally increasing the capacitance on SYS. The maximum amount of capacitance that can be used on SYS is 100uF, as shown in section 7.2.2 of the BQ25186 datasheet.

Increasing the SYS capacitance will increase the inrush current from BAT to SYS during the ship mode exit. However, as long as this inrush current is less than the configured BATOCP threshold, the SYS capacitors will charge, and there will be more stored charge on SYS to help supply the load inrush current.

To clarify my comment about VSYS_SHORT, if SYS cannot support the load applied to it, the SYS capacitors will discharge, causing VSYS to fall. If VSYS falls below the VSYS_SHORT threshold, then the system short protection will trip.

Best regards,

Alec

I did get everything to work as expected by designing and buiding my own slew rate limiter using a PFET and caps.

There was more capacitance on the VSYS rail than I expected so I needed to slow down the inrush to get the charger ro come out of SHIP mode.

Unfortunately that part will not work. In order for my slew rate limiter to work I had to slow down a 24V rail that drives a motor. The TPS22917 is not able to do that.

Hi Dan,

That makes sense. Did the PFET circuit need to be placed after the boost converter to be able to exit ship mode? Was the eFuse placed before the boost (on SYS) when it didn't work?

Yes, I placed the PFET after the boost and I trtied the eFuse before. I think what happened is once the input to the boost rose to

compliance levels the 24V output tried to rise fast and it was the same problem. By putting the slew limiter after the boost the 24V rail itself was slowed dow.