BQ2409x how to return from current fold buck

Kuramochi Tadahiko

Guru 28715 points

Hi,

I have some questions.

1. There is LDO Mode on figure 15.

How is this mode? There is no mention on the datasheet.

2. There is LDOHYS on figure 15.

What is this? There is no mention on the datasheet.

3. On P22. of datasheet there are such a following description.

"Once the thermistor reaches ≈–10°C the TS current folds back to keep a cold thermistor (between –10°C and –50°C) from placing the IC in the TTDM mode."

But on figure 15 the device becomes TTDM after Cold Fault.

Which is correct?

4. After folding back how much is VTS when ITS returns to 50uA ?

Thanks and Regards,
Kuramochi

over 10 years ago

0 Wenjia Liu over 10 years ago

TI__Expert 7730 points

Hello Tadahiko-san,

To answer your questions:

1. The LDO mode refers to the same mode as TTDM, in which the TS function, charging termination, battery detection and safety timer are all disabled.

2. Similarly, the VLDO_HYS refers to the VHYS_TTDM(TS) which is in the spec table on page #9.

3. As you can see in figure 15, the cold fault happens as soon as the "Cold Operation" ends and the during whole "Cold Fault" period the TS current is reduced to keep the IC from entering the TTDM mode.

4. After cold fault, the TS current will fold back to ~5uA and will not returns to 50uA. As soon as the temperature rises above -10C, the current will be back to 50uA.

Thanks,

Wenjia

0 Kuramochi Tadahiko over 10 years ago in reply to Wenjia Liu

Guru 28715 points

Wenjia-san,

Thank you for your reply.

Please let me confirm the VTS when the TS current returns to 50uA.
When the Its drops 50uA → 5uA(1/10) the Vts drops to 160mV (≒1600mV(VTTDM(TS))×1/10).
So, I think that the VTS is approximately 60mV(=160mV - 100mV(VHYS_TTDM(TS) ) when the TS current returns to 50uA .
Is it correct?

Thanks and Regards,
Kuramochi

0 Wenjia Liu over 10 years ago in reply to Kuramochi Tadahiko

TI__Expert 7730 points

Kuramochi-san,

Please refer to page 5 and 6 of the datasheet. The Battery-Pack NTC Monitor section has all the VTS values that are corresponding to different temperatures. When the temperature rises from cold fault，the Its will resume to 50uA and the VTS should be between 1600mV and 1200mV which is the threshold for 0 degree.

Thanks,

Wenjia

0 Kuramochi Tadahiko over 10 years ago in reply to Wenjia Liu

Guru 28715 points

Wenjia-san,

Thank you for your information.

I understood the Vts after the Its resumes to 50uA.
How much is the Vts just before the Its resume to 50uA?

Thanks and Regards,
Kuramochi

0 Wenjia Liu over 10 years ago in reply to Kuramochi Tadahiko

TI__Expert 7730 points

The Vts is around 1.475V before Its resumes to 50uA.

Thanks,
Wenjia

0 Kuramochi Tadahiko over 10 years ago in reply to Wenjia Liu

Guru 28715 points

Wenjia-san,

Thank you for your comment.

I understood not to have the the hysteresis voltage when the Its resumes to 50uA.

(The VHYS_TTDM(TS) is not applied when the Its resumes to 50uA.)

And, is the following"Time vs Temperature and VTS" correct?

Thanks and Regards,

Kuramochi

0 Wenjia Liu over 10 years ago in reply to Kuramochi Tadahiko

TI__Expert 7730 points

Kuramochi-san,

The Vts that was shown in the plot is not correct. The lower the temperature, the higher the voltage. Even after the Its is reduced, the Vts is still above ~1.2V which is the threshold for 0 degree. The threshold for ITS fold back is about 1.475V and Vts will stay above this voltage if the temperature stays below -50C.

Thanks,
Wenjia

0 Kuramochi Tadahiko over 10 years ago in reply to Wenjia Liu

Guru 28715 points

Wenjia-san,

Thank you for your support.

I'm sorry for my misunderstanding.

I have modified the plot.

Could you please confirm it?

Thanks and Regards,

Kuramochi

0 Wenjia Liu over 10 years ago in reply to Kuramochi Tadahiko

TI__Expert 7730 points

Yes, it is correct.

Thanks,

Wenjia

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BQ2409x how to return from current fold buck