BQ24253: EN pin pull up source

Kazuki Kuramochi

Part Number: BQ24253

Hello Expert,

I have question for the circuit design of BQ24253.
Our customer plat to pull up EN pin through Vsys.
However, I cannot found any comment when Vsys is enabled.
So I worried about that Failing EN detection due to Vsys is disabled during EN detection.

Do you tell me whether there is any concern when we connecting EN to Vsys though pull-up resistor?

Thank you and best regards,
Kazuki Kuramochi

over 2 years ago

0 Jeff F over 2 years ago

TI__Guru*** 149265 points

Hi Kazuki,

Per the abs max table, ENx can be pulled up to 7V max so pulling up to VSYS is okay.

Regards,

Jeff

0 Kazuki Kuramochi over 2 years ago in reply to Jeff F

TI__Genius 9160 points

Hello Jeff,

Thank you for your prompt reply.
I understood there isn't any issue from the point of view of AbsMax.
However, I cannot found any explanation regarding the timing of Vsys start to supply.

Does Vsys start to supply at the same time as Vin is applied?

Thank you and best regards,
Kazuki Kuramochi

0 Jeff F over 2 years ago in reply to Kazuki Kuramochi

TI__Guru*** 149265 points

HI Kazuki,

If battery is attached, SYS=BAT will be available. If battery is not attached, SYS will not be available until D+/D- completes, which varies depending on the input source attached but could be up to 1 second.

Regards,

Jeff

0 Kazuki Kuramochi over 2 years ago in reply to Jeff F

TI__Genius 9160 points

Hi Jeff,

There is the case of waking up without battery in customer's use case.
The chart of "figure18 bq24253 D+/D- and EN1/EN2" said EN1/2 detection is later than D+/D- detection.
Based on your explanation, could I regard that EN1/2 detection will proceed after VSYS is available during the condition of battery isn't connected?

Also, could you tell me when LDO is enabled in figure18?
I'll suggest to use LDO out for pull-up power source if there is possibility that VSYS doesn't wake up during EN1/2 detection.

Best regards,
Kazuki Kuramochi

0 Jeff F over 2 years ago in reply to Kazuki Kuramochi

TI__Guru*** 149265 points

Hi Kazuki,

D+/D- must complete before EN1/EN2 are read (unless they are both high, which is HiZ as I recall). Also, EN1/EN2 must make a state change after D+/D- for ENx to become active.

LDO comes up after power source detection and before D+/D- starts.

Regards,
Jeff

0 Kazuki Kuramochi over 2 years ago in reply to Jeff F

TI__Genius 9160 points

Hi Jeff,

I'm also asking about when VSYS is powered-up.
Would you answer this question?

Should I change power source of pull up resistor?

Best regards,
Kazuki Kuramochi

0 Jeff F over 2 years ago in reply to Kazuki Kuramochi

TI__Guru*** 149265 points

HI Kazuki,

ENx pins are enabled after D+/D- completes, which should be after /PG pin goes low and definitely by the time SYS is up.

Regards,

Jeff

0 Kazuki Kuramochi over 2 years ago in reply to Jeff F

TI__Genius 9160 points

Hi Jeff,

Sorry for bothering you but I'd like to make sure about your comment.

My understanding is VSYS is wake up before EN detection after /PG goes low.
So they can use VSYS for pull up power source of ENx pin.

Is this right?

Also, if VSYS will wake up after D+/D- detection, Can this behavior triggers ENx detection when ENx is connected to VSYS?

Best regards,
Kazuki Kuramochi

0 Jeff F over 2 years ago in reply to Kazuki Kuramochi

TI__Guru*** 149265 points

Hi Kazuki,

Yes, SYS can be used to pull up ENx.

Regards,

Jeff

0 Kazuki Kuramochi over 2 years ago in reply to Jeff F

TI__Genius 9160 points

Hi Jeff,

I'm not just asking whether they can use VSYS for pull-up.
I'm also asking about whether they can use VSYS start-up for overwriting ILIM setting from D+/D- detection by ENx detection.

Would you provide your opinion for this perspective?

Best regards,
Kazuki Kuramochi

0 Jeff F over 2 years ago in reply to Kazuki Kuramochi

TI__Guru*** 149265 points

Hi Kazuki,

Yes. SYS does not come up until D+/D- completes.

Regards,
Jeff

0 Kazuki Kuramochi over 2 years ago in reply to Jeff F

TI__Genius 9160 points

Hi Jeff,

Sorry for bothering you again and again.
However, I'd like to make sure about start-up procedure.
I made flow chard at Start-up when they pulling-up ENx for Vsys as below.

Is this understanding correct?

Also, BQ24253 cannot detect ENx at start-up when they pull-up ENx by internal LDO output.
This is because, this pin will wake-up before starting D+/D- detection.

Is this understanding right as well?

Best regards,
Kazuki Kuramochi

0 Jeff F over 2 years ago in reply to Kazuki Kuramochi

TI__Guru*** 149265 points

Hi Kazuki,

Yes, your flowchart illustrates my understanding. I am still waiting on some ICs to test on the bench.

Regards,

Jeff

0 Kazuki Kuramochi over 2 years ago in reply to Jeff F

TI__Genius 9160 points

Hello Jeff-san,

Thank you for your explanation.
As far as my understanding, LDO out wake up before D+/D- detection.
So ENx cannot activate by LDO out start-up against D+/D- detection.
is this correct?

Best regards,
Kazuki Kuramochi

0 Jeff F over 2 years ago in reply to Kazuki Kuramochi

TI__Guru*** 149265 points

Hi Kazuki,

That is correct.

Regards,

Jeff

0 Jeff F over 2 years ago in reply to Jeff F

TI__Guru*** 149265 points

Hi Kazuki,

I apologize. I was wrong about several items. SYS comes up when LDO comes up as shown in the plot below so it cannot be used to indicate D+/D- complete. /PG is the signal that indicates when D+/D- completes and ENx lines are active. You could use a PFET with gate driven by /PG to turn on ENx lines pullup. Keep in mind that would count as the status change from ENx=Low to something different.

Please note the following:

1. LDO needs a 1kohm resistor to ground in order to slow its startup or ILIM pin may be ignored and ILIM set to max.

2. If D+=D-,as in the case of a DCP adapter, ILIM and VINDPM are set by external resistors on those pins regardless of ENx pin status.

3. For other D+/D- detection, VINDPM is 4.8V and ILIM is set as detected until ENx status change.

Because of item 2, I recommend setting EN1=high and EN2=low all the time and use external resistors to set ILIM and VINDPM.

Regards,

Jeff

0 Kazuki Kuramochi over 2 years ago in reply to Jeff F

TI__Genius 9160 points

Hello Jeff-san,

Thank you for your kindly support.

I understand but I'd like to confirm about test condition.
I think you don't connect battery during this test.
Is this understanding correct?

Best regards,
Kazuki Kuramochi

0 Michael Emanuel35 over 2 years ago in reply to Kazuki Kuramochi

TI__Mastermind 34325 points

Hello Kazuki-san,

I will get back to you by next Monday.

Thanks,

Mike Emanuel

+1 Michael Emanuel35 over 2 years ago in reply to Michael Emanuel35

TI__Mastermind 34325 points

Dear Kazuki-san,

I verified the waveform and there was indeed no battery connected.

Thanks,

Mike Emanuel

Please click "Resolved" if this answered your question.

0 Kazuki Kuramochi over 2 years ago in reply to Michael Emanuel35

TI__Genius 9160 points

Hello Mike-san,

Thank you for your confirmation.
I understand.

Thank you and best regards,
Kazuki Kuramochi

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BQ24253: EN pin pull up source