BQ51050B: disable the charger

Hi Bill,

I think this takes too long.  What happens to the current coming out of BAT when you make TERM 0 volts.

thanks

Phil

Hi Bill,

I found the following from an old post

Tony,

I did some more checking on this.  After discussions with the designer and bench verification, the TERM pin holds the key.

The TERM pin has a comparator that checks the ILIM voltage in relation to the TERM voltage.  When IOUT drops, the ILIM voltage follows.  As the ILIM voltage drops, the TERM comparator will trip when it reaches the termination current.

If the TERM pin is floated, the comparator is disabled.  At that point, there will be no termination.

If the TERM pin is grounded, the effect is quite similar.  The ILIM pin can not go below 0V.  However, due to comparator offset and accuracy it would not necessarily be as consistent as floating.

There is a fast-charge time-out of ~10 hours.  The bq51050B will send an EPT (Battery Failure).  The TX will stop power transfer at that time.  TI Transmitters will not restart power transfer.  That is not a WPC requirement.

Regards,

Dick

so I do not thinking taking TERM to ground will disable the charging.

Phil

Hi Phil

The above info is from a post by Dick Stacey in 2015:

https://e2e.ti.com/support/legacy_forums/wireless_power/f/693/p/394794/1404022

The question and solution is how to disable termination and above is the right approach.  With TERM Float or Ground the device will not terminate, send charge complete EPT, voltage will remain applied to pack. 

NOTE the caution regarding 10 hr safety timer.

This will NOT stop or disable charge only termination.

Another possible option. Combine the above Termination disable with reduce charger current.

The charge current is set by ISET/FOD resistors, low value is high charge current and high value is low charge current.  A mosfet could be used to switch in resistors to increase current to desired fast charge current. 

Possible Charge Disable could be termination disable and charge current reduced to low level.

Thanks Bill .  adding parts to my layout is not an option at this time.

So I will go with taking TS_CTRL high which will cause the BQ51050B to send End Power Transfer (EPT) and TX will turn off. 

I need to know how long this takes.  Since messages are exchanged at about 32 ms intervals it will take at least that long

for the TX to turn off.  Then the BQ51050B will take some time to shut down once it has no power.  I will have to look for this

in the data sheet or measure it.

I assume that as long as I hold TS_CTRL high I assume the BQ51050B will not try to restart.

I do not care about how long it takes to restart.

thanks for your help and patience

Phil

Hi Bill,

I am using an NXQ1TXH5 wireless power transmitter.

In my MCU I took the TS_CTRL pin high for 10 ms. and about 40 ms from the rising edge of this signal the current from the BQ51050B dropped to zero as expected.

What I would like to know is how long must I hold TS_CTRL high for the BQ51050b to send and EPT signal to the NXQ1TXH5 ?

If I hold the TS_CTRL line high for 100 ms then NXQ1TXH5 goes to a fatal error state after pinging the BQ51050B three times.  So my second question is will the BQ51050B respond to a request from the wireless power chip to restart if the TS_CTRL line is high ?

thanks

Phil

Hi Phil

The TS_CTRL has a 10mS deglitch time, typical value. If you hold it high for 15mS that would be long enough.

Then RX will send EPT00 and this will take about 40mS. Most TX shuts down right after the EPT is decoded.

If TS_CTRL is held high it will not restart.  It will go thru SS/ID/Conf phase but not enable output, EPT sent again.

thank you

HI Bill

I made TS_CTRL go high for 15 ms and the NXQ1TXH5 wireless transmitter dropped the power about 40 ms after the rising edge on TS_CTRL.

This worked weill except that about 33% of the time the NXQ1TXH5 went into a "fatal" state.  It remains in this state unless you remove the wireless power transmitter and put it back or if you just wait 10 minutes.  I have sent logs to the NXP support team.

I think the problem might be the EPT00 code the BQ51050B but I am not sure . I am waiting to hear from NXP and will keep you posted.

Phil

Hi Bill,

we are going to change the layout so we can add some parts if you have a better way of shutting down the current.  I need to get it close to zero amps since the fuel gauge will only allow 6ma of current to flow.

thanks

Phil