TPS65219: TPS65219-08 design and programming questions

Hi Aaron,

I am checking with my other team members but i don't see any other Buck design tools. Even though the design started off from an existing IP, there must haven been changes made specific to this device.

2x is generalized guidance (similar to capacitor deratiing) as we don't want to operate anywhere near the saturation value of the Inductor. Please also remember that we need to account for temperature variation.

Ripple is higher in PFM compared to PWM. The D/S specifies the value in both modes.

There is a user programmable version of this device (TPS6521905) where customer can program the rail voltage, power up and power down sequencing. Please refer to the below NVM programming guide on how to do that.

https://www.ti.com/lit/ug/slvucm5/slvucm5.pdf?ts=1738361643398&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS6521905

Sathish

Is this the one to use?  My thought was this one.

 https://dev.ti.com/gallery/info/PMIC/TPS65219_GUI/

Thank you Sathish, here are a few more questions from the customer:

Question1: For LDO outputs that are enabled in the ’08 PMIC but not used in our design – do we need Cin / Cout caps on them at all?  I plan to disable them via I2C after the AM625 is up, but need the PMIC power-up sequence to complete for that to happen…

Question2: Checking out the NVM programming guide…. I do see where voltage ripple is specified for PFM and PWM modes, but as far as ripple current, I only see the the BuckN current ratings in the spec table - for example

And the design guidelines down in section 8

Inductor Selection - Buck1, Buck2, Buck3

Internal parameters for the buck converters are optimized for 0.47uH inductor. DCR must be 50 mO or lower. Ensure that the selected inductor is rated to support saturation current of at least 7.4A for Buck1 and 5.4A for Buck2/Buck3.

The target is a space constrained application – so trying to identify the smallest package size inductor that we can get by with for the Vin/Vout and expected Iout current in our application.  The inductor Isat in section 8 gives a bit of margin above from the peak current limit from the specification tables, but I believe that peak current limit could be quite a bit lower in this application with a 3.7V Vin, Iout quite a bit lower than Iout-max and using the forced PWM setting.

As an example, using TI’s ripple current guide, I get a nominal ripple current of ~0.8A for forced PWM mode (with 2.3 MHz Fsw) compared to what looks like roughly a 3.4A  max ripple current from the spec table….I can get to much smaller size inductor packages if I can justify taking advantage of lower I-sat requirements based on our usage – trying to verify that the process we use to reduce the max values from the data sheet are valid.

Hi Lucas,

Regarding Question1 on LDOs -> Cin is not of a much concern but i am suspecting if LDO output oscillates because of the missing output cap. TPS65219 has fault detection on Buck and LDO outputs and that could trigger a shutdown event and would never be able to powerup. I would recommend to try it out the desired case to make sure it works for sure.

Regarding Bucks, what is the maximum Iout? I-sat comes from the peak current limit and smaller inductor would increase the ripple. You need to make sure the appropriate output cap is used and the frequency response of the Buck need to be verified. Since TPS65219 is designed for 470nH all these behaviors are not verified.

Sathish

So the question is determining what the ripple current looks like for our particular application….Vin is 3.7 V

 Buck 1 – Iout = 3.0A, 0.85 V

Buck 2 – Iout = ~300mA, 1.8V

Buck 3 – Iout = ~300mA, 1.1V

 We can certainly set them to PWM only once the connected AM625 boots as well…