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# LM5161-Q1: The variation of ton

Part Number: LM5161-Q1

Hi,

We got a question from the customer about LM5161-Q1.
Could you help us?

[Question]
How much is the variation of the constant 1.008*10^(-10) under the following condition?

Topology: Inverting Buck-Boost
Vin: 6~32V, 6~20V
Vout: 8V

They are concerned about reaching the current limit due to the variation of ton. Therefore they need this to estimate ton.

Best Regards,
tateo

• Hello,

In order to understand the variation of TON, you can find the variation of TON across the VIN range for given RON values in the typical characteristics section of the datasheet. I would recommend looking at Figures 10 and 11 to get an idea for the variation of on time.

Also, the device will enter current limit when the peak current exceeds 1.6A (typical) and at this point the ON time will immediately terminate, which means the off timer will be initiated to protect the device. The length of the OFF-time is controlled by the FB voltage and the input voltage VIN.

Best Regards,
Katelyn
• In reply to Katelyn Wiggenhorn:

They are concerned about the inductor current hits the current limit. The ton varies by the IC at one condtion. For example, IC-A has short ton which the inductor current doesn't hit the current limit, but IC-B has long ton which makes the current limit condition.

We assume we can estimate the variation from the datasheet section 6.6. But it seems to depend on VIN condition and becomes worse as the input voltage increases. Therefore they want to make sure the variation at their own condition. Could you provide the variation of the constant 1.008*10^(-10)? We don't need guarantee. They will use it as reference.

Topology: Inverting Buck-Boost
Vin: 6~32V, 6~20V
Vout: -8V

Best Regards,
tateo

• In reply to Katelyn Wiggenhorn:

Hi, There was typo on previous post. Vout is -8V. I corrected that and inform you.

Best Regards,
tateo

• In reply to Katelyn Wiggenhorn:

Hi, Is there any update on that. If you need more information for this, I could send it by e-mail. Could you provide your e-mail address?

I would appreciate it, if you could give us your feedback.

Best Regards,
tateo

• In reply to tateo yamashiro:

Hi Tateo,

You can calculate the Ron by using the information in section 7.3.6 of the datasheet.

You can see that: "RON must be selected for a minimum on-time (at maximum VIN) greater than 150 ns for proper operation. This
minimum ON-time requirement limits the maximum switching frequency of applications with relatively high VIN
and low VOUT."

As you mention, the RON should be calculated for the maximum VIN case since this is the limitation for Constant On time operation.

Can you share the schematic for your design? If necessary, you can send to my e-mail (k-wiggenhorn@ti.com).

In parallel, I will reach out to the product expert to see if we have any additional information on the constant from the datasheet.

Best Regards,
Katelyn Wiggenhorn
• In reply to Katelyn Wiggenhorn:

Hi, I have sent you an e-mail. Have you received it? We would appreciate it if you give us your feedback.

Best Regards,
tateo

• In reply to tateo yamashiro:

Hi Tateo,

Yes, I received this e-mail, and I will share feedback today.

Thank you,
Katelyn Wiggenhorn
• In reply to Katelyn Wiggenhorn:

Hi Tateo,

Let's continue this discussion via e-mail, and I will close this e2e thread.

Best Regards,
Katelyn