TPSM63608: RBOOT and CBOOT

Vidhya J

Intellectual 400 points

Part Number: TPSM63608

Tool/software:

Hi Team,

What is the current limit on RBOOT and CBOOT pins?

Voltage on these pins is specified as max 5.5V in datasheet.

Regards,

Vidhya

9 months ago

0 Niranjan Nair 9 months ago

TI__Genius 9100 points

Hi Vidhya,

May I know what you need this information for? If it is for selecting Rboot, the range is mentioned in the datasheet (0 to 500 ohms).

Thanks and regards,

Niranjan

0 Vidhya J 9 months ago in reply to Niranjan Nair

Intellectual 400 points

Hi Niranjan,

I need to check the derating for the resistor. 0.1W , 0Ohms, 0402 package resistor?

What is the current?

Regards,

Vidhya

0 Niranjan Nair 9 months ago in reply to Vidhya J

TI__Genius 9100 points

Hi Vidhya,

Rboot does not carry a DC current, it carries the charging and discharging current for the bootstrap capacitor. So the power dissipation in it would be very low. 0.1 W should be more than enough and it is the value used for Rboot in EVMs of other devices in the family.

Please refer to the following thread for more information on power dissipation : https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1060174/faq-tps546d24a-selecting-rboot-and-calculating-rboot-power-dissipation

Regards,

Niranjan

0 Vidhya J 9 months ago in reply to Niranjan Nair

Intellectual 400 points

Hi Niranjan,

The link shared, has power dissipation formula. But I don't have enough data to calculate the same.

Pdiss = R * I^2 * Sqrt ( D)

Rboot * [ (Vdrive - Vplat) / (Rdrive + Vboot) ] ^2 * [ Qg * (Rdrive + Rboot) / { (Vdrive - Vplat) * Tsw } ]

Can you share details to justify 0Ohm, 0.1W, 0402 package will suffice?

Thanks and Regards,

Vidhy

0 Niranjan Nair 9 months ago in reply to Vidhya J

TI__Genius 9100 points

Hi Vidhya,

The above formula can be used when all the FET parameters are known, for an external FET device. I shared the link to show that the typical power dissipation would be very low, in the range of few mW. If you plug in 0 Ohms in the formula, it will anyway give the answer as 0. In this case the power would be dissipated in the parasitics.

0.1 W, 0402 package Rboot is what is used in EVMs of this family of devices and this rating is more than sufficient.

Regards,

Niranjan

0 Vidhya J 9 months ago in reply to Niranjan Nair

Intellectual 400 points

HI Niranjan,

0 ohms will consider 0.005Ohms considering tolerance. so, for the purpose of justification any calculation that can be done for TPSM63608?

Also, Any RC snubber provision can be provided on the SW pin of the IC TPSM63608? or it is taken care internally via SPSP feature? Kindly suggest.

Thanks and Regards,

Vidhya

0 Niranjan Nair 9 months ago in reply to Vidhya J

TI__Genius 9100 points

Hi Vidhya,

Calculating the exact dissipation will be difficult since the parameters of the internal FET are not publicly available. In any case, the dissipation will be well below 0.1 W.

There is no provision to connect RC snubber, the SW pin should not be connected to any external component or signal. Since the device is a module, the expected parasitics and SW node ringing is lower compared to discrete implementations.

Regards,

Niranjan

0 Vidhya J 9 months ago in reply to Niranjan Nair

Intellectual 400 points

Hi Niranjan,

ok.

can connect optional 1uF cap on the VCC pin of TPSM63608RDFR.

Thanks and Regards,

Vidhya

0 Niranjan Nair 9 months ago in reply to Vidhya J

TI__Genius 9100 points

Hi Vidhya,

There is an internal 1 uF capacitor on the VCC pin. There is no need to connect an external capacitor. You can connect an optional capacitor on the VLDOIN pin to improve noise performance.

Regards,

Niranjan

0 Vidhya J 8 months ago in reply to Niranjan Nair

Intellectual 400 points

ok Niranjan,

To connect VLDOIN to VOUT, should connect any 0 Ohm resistor? or can directly short? can add a 0.1uF cap close to VLDOIN pin?

Thanks,

Vidhya

0 Vidhya J 8 months ago in reply to Vidhya J

Intellectual 400 points

Also, what should be the CFF for the following Output voltages

5V 22pF

3.3V 47pF

1.8V 100pF as per table 8-1 in datasheet.

what value to be used for 1.5V, 1.05V? there is no formula.

0 Niranjan Nair 8 months ago in reply to Vidhya J

TI__Genius 9100 points

Hi Vidhya,

You can do either direct short or through 0 ohms, it should not make a difference. Only thing is Vout should be less than 12 V.

Yes, a 0.1 uF capacitor can be added close to the pin for better noise immunity.

Regards,

Niranjan

+1 Niranjan Nair 8 months ago in reply to Vidhya J

TI__Genius 9100 points

Hi Vidhya,

CFF needs to be used only when output capacitance is close to the minimum required value or transient response is unsatisfactory. For the optimum CFF value the crossover frequency has to be determined experimentally.

Please refer to the following application note for information : https://www.ti.com/lit/an/slva289b/slva289b.pdf

Regards,

Niranjan

0 Vidhya J 8 months ago in reply to Niranjan Nair

Intellectual 400 points

HI Niranjan,

How to connect VLDOIN if the VOUT is <3.1V??

Refer to the statement from datasheet. "If the VLDOIN voltage is less than 3.1 V, VIN1 and VIN2 directly power the internal LDO".

Thanks,

Vidhya

0 Niranjan Nair 8 months ago in reply to Vidhya J

TI__Genius 9100 points

Hi Vidhya,

You can still connect to VOUT/ground VLDOIN in that case. Either way the internal LDO will be powered by VIN1 and VIN2.

Regards,

Niranjan

0 Vidhya J 8 months ago in reply to Niranjan Nair

Intellectual 400 points

Hi Niranjan,

VLDOIN cannot be left floating? and it has to be connected to either VOUT or ground?

Thanks,

Vidhya

+1 Niranjan Nair 8 months ago in reply to Vidhya J

TI__Genius 9100 points

Hi Vidhya,

It has to be connected to VOUT (unless VOUT > 12V) or ground.

Regards,

Niranjan

0 Vidhya J 8 months ago in reply to Niranjan Nair

Intellectual 400 points

Thanks Niranjan.

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TPSM63608: RBOOT and CBOOT