TPS25940-Q1: Current limit and Shutdown mode

Hi Tateo,

I'm moving this thread to the appropriate forum.

-Aramis

Hi Tateo,

May I know where this device is going to be used by the customer?
What is the application use case? and Requirements?
The device monitors load current using Rds(on) drop.
To detect overload condition, the device does not need 1V drop across it. The device detects over-current whenever the load current exceeds set current limit value. The datasheet mentions under a typical test condition.
Are you talking about difference between thermal shutdown and shutdown control.?

Regards,
Rakesh

Thank you for your reply.
We'll send you a project detail by e-mail.

According to datasheet, the device has two different EN/UVLO threshold voltage. What's the difference of two threshold except for supply current?

Best Regards,
tateo

Thank you for your reply.

They have additional question. The variation of Rds(on) is over +/-50% at over temperature.
They are thinking that if the device monitors load current using Rds(on) drop, current limit accuracy might be over +/-50%.
Does the device have compensation circuit?

Best Regards,
tateo

Thank you for your support.
They consider to control EN/UVLO by MCU GPIO. If GPIO low-level output voltage is 0.4V, two case might be happend that detecting threshold voltage for low Iq or not.
Is there any concerns this usage? Should they input either threshold voltage for EN/UVLO?

UVLO threshold: 0.63~0.9V
Low Iq threshold: less than 0.3V
-> Should they input either threshold voltage for EN/UVLO?

Best Regards,
tateo

Hi Tateo,

Either of the threshold voltage EN/UVLO can be used to control the device.
There should not be any concern from device functional perspective.

Regards,
Rakesh

Thank you for your reply. Our customer has additional question.
Could you provide internal circuit of detecting current limit? And what is related with the variation of current limit threshold except for accuracy of the resistor?
They are worried that equation 4 and electrical characteristics are not match.

Best Regards,
tateo

Hi Tateo,

We cannot share internal circuit details or methods used to achieve specific function.
We guarantee the data mentioned in the Electrical Characteristics table of the datasheet when the device used under recommended operating conditions.

Can you please elaborate what exactly not matching with relate to equation 4. Are you referring to typical ILIM values?

Thanks
Rakesh

Hi, Sorry to bother you again. We got an additional question. Could you help us?

- How much is the current limit accuracy except for the variation of R(lim)?
- Does the I(lim) value in EC table include the variation of R(lim)?
  These value are measured Pulse-testing. So I think the variation of R(lim) is included.
- If the I(lim) value in EC tavle include the variation of R(lim), how much is the accuracy of R(lim) did you use for measurement?
- If they use R(lim)=40k, how much is the variation of I(lim)? They would like to make sure estimation method.

According to top page of datasheet, 0.6-A to 5.3-A adjustable current limit (+/-8%). But several value in EC table is out side of +/-8% from caluculated value of equation 4.
So they want to know above question.

Best Regards,
tateo

Hi Tateo,

Figure 17 in the datasheet shows the variation of I(lim) at various current limit settings.  As shown in Fig 17, the accuracy go beyond +/-8% at lower currents. The variation of R(lim) is not included in the EC table. To keep the minimal effect of R(lim) variation on current limit accuracy, we recommend to use standard 1% tolerance for R(lim).

What level of accuracy is the target for the customer? and any specific reason for this?

Best Regards,

Rakesh

Thank you for your reply. They are concerned about below points.

- I(lim) typical value in EC table is not match with calculation result from equation (4).
  They want to know how the typical value was specified.

- I(lim) minimum and maximum value in EC table are out side of +/-8% from calculation result from equation (4).
  ex. I(lim)=5.27A -9.23% / +6.72% at R(lim)=16.9k
  They want to know how to estimate the typical value and the variation.

- They consider to use R(lim)=40k. They would like to make sure how much is the variation of I(lim).

Best Regards,
tateo

Hi Tateo,

The I(lim) values mentioned in the EC table are based on the large sample tested data. The min, max values are derived based on possible worst case calculations including process, temperature, measurement errors.
The equation (4) is basically derived by data fitting the typical current limit value across wide current range. Hence, you could see minor deviation between the calculated value using equation(4) and typical value in EC table at certain current limit value.

Can you please let me know What level of accuracy is the target for the customer? and any specific reason for this?

Regards,
Rakesh

Thank you for your reply.

Actually they don't need high accuracy current limit. For example, 10% should be ok. But they need to define the variation(min, typ, max) of current limit.
So they want to know how to estimate the typical value and the variation at R(lim)=47k.
How should we suggest for customer?

Best Regards,
tateo

Thank you for your reply. Please let me confirm your suggestion?
I think we can estimate like below.

typ: 89/47 - 1.4% = 1.87A
min: 1.87*0.92*0.99= 1.70A
max: 1.87*1.08*1.01= 2.04A

Is it right?

Best Regards,
tateo

Hi Tateo,
What you estimated is correct, it should be -1.4% then the typical value will be 1.87A.

Best Regards,
Rakesh