TPS62A01: current limit

Hello Noriyuki,

Thank you for reaching out

Noriyuki Takahashi said:

1. How the device operate during over current?

Noriyuki Takahashi said:

2. According to the datasheet, I_HS(OC) and I_LS(OC) have different thersholds. Could you tell why these threshold are different? And which threshold they should take care, high side or low side for the overcurrent?

I see the typical value for over current limit for HS and LS as 1.8A in the datasheet. In a case if the values are different please consider the HS FET limits.

Noriyuki Takahashi said:

3. Are there any app notes to understand how the current limit operate?

See the answer for question1.

If you have any further questions please let me know.

Thank you,

Regards,

Moheddin.

Moheddin

Moheddin Pasha Shaik said:

In a case if the values are different please consider the HS FET limits.

They should use min value of HS FET that is 1.3A, right?

Are there any app notes or training videos that show how Hicupp mode operate?

Regards,

Noriyuki Takahashi

One more question.

In general, when should they use  the LS FET limits?

Regards,

Noriyuki Takahashi

Hi, I jsut found the blog below. 

https://e2e.ti.com/blogs_/b/powerhouse/posts/dc-dc-converter-datasheets-current-limit-part-one

Accoding to this, it seems that they need to use lower value, that is HS current limit in case of TPS62A01. Is this correct?

Then, in order to calculate the acutual current where the device will enter Hiccup mode,  can the equations below are used?

Regards,

Noriyuki Takahashi

Hello Takahashi,

Noriyuki Takahashi said:

In general, when should they use  the LS FET limits?

It's not about using this value, It is the maximum current limit of the LS FET, if the current through the LS FET is more than specified limit then it turns OFF.

Noriyuki Takahashi said:

Accoding to this, it seems that they need to use lower value, that is HS current limit in case of TPS62A01. Is this correct?

Yes, you can use the minimum value of the HS FET current limit, which is 1.3A

Noriyuki Takahashi said:

Then, in order to calculate the acutual current where the device will enter Hiccup mode,  can the equations below are used?

Yes, you can use this formula, but make sure that it will be the minimum value of IOUT to reach Hiccup mode.

Thank you,

Regards,

Moheddin.

Moheddin,

Please let me confirm my understanding again, because this is confusing.

In HICCUP mode, can the upper threshold and lower threshold be defined as the attached?

And can High-side peak current limit and Low-side valley current limit be also used in the equations in the attached?

definition.pptx

Regards,

Noriyuki Takahashi

Hello Noriyuki Takahashi,

Noriyuki Takahashi said:

In HICCUP mode, can the upper threshold and lower threshold be defined as the attached?

The upper threshold is maximum HS FET current limit as defined in the datasheet, in your case as per the formula it is I peak. The lower current limit is something different, let me explain you in this way, during the high side FET is ON, the energy is stored in the inductor and once it reaches the maximum current, the high side FET is OFF and low side FET is ON, in this case the energy stored in the inductor is discharged. when all the energy that is stored is discharged then the high side FET is ON again and this process repeats.

Thank you,

Regards,

Moheddin.

Moheddin,

Thanks. I invetigated more about the valley inductor current limit. Please let me confirm my understanding. This is confusing..

The peak inductor current limit & the valley inductor current limit work as the link below. Is this correct?

https://e2e.ti.com/blogs_/b/powerhouse/posts/understanding-valley-current-limit

Looking at other device datasheet, e.g. TPS562212, it seems that both the peak inductor current limit & the valley inductor current limit can work as below. TPS62A01 can also support both the peak inductor current limit & the valley inductor current limit. Is this correct?

Regards,

Noriyuki Takahashi

Hello Noriyuki Takahashi,

Noriyuki Takahashi said:

The peak inductor current limit & the valley inductor current limit work as the link below. Is this correct?

https://e2e.ti.com/blogs_/b/powerhouse/posts/understanding-valley-current-limit

Yes, peak current limit and valley current limit works differently. It depends upon the control topology of the device.

For example TLV62565 works with Adaptive On-Time Current Control, which detects the valley current limit to turn ON the high-side FET.

Please refer page no.9 in the datasheet - TLV6256x 1.5-A High Efficiency Step-Down Converters in SOT-23 5-Pin Package datasheet (Rev. D) (ti.com)

But TPS62A01 works with Adaptive Off-Time Current Control, which detects the peak current limit to turn OFF the high side FET and turn ON on the low side FET.

Please refer page no.9 in the datasheet - TPS62A0x and TPS62A0xA, 1-A and 2-A High-Efficiency Synchronous Buck Converters in a SOT-563 Package datasheet (Rev. B) (ti.com)

Noriyuki Takahashi said:

 TPS62A01 can also support both the peak inductor current limit & the valley inductor current limit. Is this correct?

No, it supports peak inductor current limit only as explained in my previous reply.

I hope it make clear now.

Thank you,

Regards,

Moheddin.

Moheddin

Thanks a lot!

Maybe, this is the last question.

Moheddin Pasha Shaik said:

 TPS62A01 can also support both the peak inductor current limit & the valley inductor current limit. Is this correct?

No, it supports peak inductor current limit only as explained in my previous reply.

Why  the valley inductor current limit is specified in the datasheet? It seems the valley inductor current limit can't be used in order to design the schematic, because TPS62A01 can support only the peak inductor current limit.

Regards,

Noriyuki Takahashi