BQ25710EVM-017: Sinusoidal BATFET gate and battery current

Zhen Kit Ho

Part Number: BQ25710EVM-017
Other Parts Discussed in Thread: BQSTUDIO, , BQ25713

Hi,

I am experiencing a sinusoidal waveform for the BATFET gate and battery current. The two waveforms seem to be quite in phase. I believe this also resulted in inaccurate read back of the battery charge current. The battery charge current on the BqStudio seems to increase to 2A as the battery is being charged, but during the process the scope has shown this sinusoidal wave form.

Hence I wanted to ask if:

1) The waveforms are an abnormal occurrence?

2) The increasing current on the battery as it is being charged is normal as well?

3) Does the battery charger have constant current charging? If so, why does the current rise? I am using a 1A constant current electronic load and the supply is 24V,3.75A

Best Regards,

Zhen Kit

over 5 years ago

0 Tiger Zhou over 5 years ago

TI__Mastermind 32745 points

Did you test on BQ25710EVM-017 or your own circuit?

0 Tiger Zhou over 5 years ago in reply to Tiger Zhou

TI__Mastermind 32745 points

This waveform is abnormal. It has low frequency oscillation, which may result from your test setup. Sometimes, lack of input and output caps may result in unstable operation.

0 Zhen Kit Ho over 5 years ago in reply to Tiger Zhou

Intellectual 290 points

Hi Tiger,

Yes i tested this on the BQ25710EVM, with just a 4 pin battery connector attached to the V_BAT output and a DC electronic load connected to the V_SYS and a programmable DC power source.

From further testing, I notice that supplying an V_IN roughly 1.2V higher than the V_SYS and V_BAT would result in this low frequency oscillation. The frequency of the oscillation increased as V_IN was increased.

It was also noted that under the circumstance that V_SYSMIN < V_IN < V_SYS + 1.2V, the EVM exhibits more normal behaviour as shown below:

Best Regards,

Zhen Kit

0 Zhen Kit Ho over 5 years ago in reply to Zhen Kit Ho

Intellectual 290 points

Hi TIger,

I have tested this with a different EVM as well. I still am having the same sinusodial result.

Best Regards,

Zhen Kit

0 Tiger Zhou over 5 years ago in reply to Zhen Kit Ho

TI__Mastermind 32745 points

Hi, Zhen Kit,

Could you specify your test conditions? Did you use a battery? My suggestion is to follow our user's guide when evaluating the EVM.

0 Zhen Kit Ho over 5 years ago in reply to Tiger Zhou

Intellectual 290 points

Hi Tiger,

Currently I am testing with a 18V,,5A source, 1A CC electronic load at V_SYS and V_SYS = 16.5V.

A 4S Li-Ion Battery was used.

Could it be due to PFM mode?

Best Regards,

Zhen Kit

0 Zhen Kit Ho over 5 years ago in reply to Zhen Kit Ho

Intellectual 290 points

Hi Tiger,

Just an update, we tested it using two electronic loads as suggested in the EVM test setup and there was no issue.

The issue seems to lie with the interaction between the smart 4S Li-Ion Battery and the battery charger.

Could I just inquire if this battery has been seen with other smart batteries?

Best Regards,

Zhen Kit

0 Tiger Zhou over 5 years ago in reply to Zhen Kit Ho

TI__Mastermind 32745 points

Hi, Zhen Kit,

If the charge/load current is low, the part will operate in PFM mode. In this mode, there may be pulse-skipping, which causes elevated ripple current. This has nothing to do with stability. When load current increases, the part exits PFM mode, the ripple reduces.

Yes, BQ25713 works with smart batteries.

0 Zhen Kit Ho over 5 years ago in reply to Tiger Zhou

Intellectual 290 points

Hi Tiger,

Thanks for all the help and apologies for the late reply. We have managed to find the source of the issue.

We had a ferrite core on the wire leading to the battery connector. By removing this core, we did not face this issue anymore.

Is there any interference that the ferrite core might cause to the EVM's functionality?

Best Regards,
Zhen Kit

0 Tiger Zhou over 5 years ago in reply to Zhen Kit Ho

TI__Mastermind 32745 points

Good to know. We also observed this type of low frequency sinusoidal waveform if the battery is connected using a long wire. It is setup-related. Since we detect battery voltage by SRN, the ferrite or parasitic inductance could cause a propagation delay, which affects the loop.

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BQ25710EVM-017: Sinusoidal BATFET gate and battery current