TPS63050: Can I apply voltage directly to VBUS pin through resistor?

Chase Jeong

Genius 5060 points

Part Number: TPS63050

Hi all,

We are testing TPS63050 chipset on my PCB, I have one question about customized circuit;

my partner gave us the schematics as below, to control VBUS voltage in three ways;

- PG pin is directly connected to MCU.

- VIN is connected to Li-ion battery that has 3.7V nominal voltage.

- VBUS_MOD is directly connected to MCU, we can make VBUS_MOD to 2.8V(MCU high output) or 0V(MCU low output)

We tested this PCB, and the result is as below;

apply voltage to VBUS_MOD=0V --> VBUS=4.1V

apply voltage to VBUS_MOD=2.8V --> VBUS=0.5V

leave VBUS_MOD as floating --> VBUS=5.05V (this is normal operation)

the schematic is working as we expected, but still I have a question that is schematic is right or not.

reference circuit in datasheet, we cannot see the resistors R3, R9, just we added it because of our specific purpose.

if you can simulate this circuit, please let me know.

and I also want to know that it is okay to use TPS63050 this way and any harmful damage to IC if I use like this.

Please check this issue. Thanks.

Best Regards,

Chase

over 3 years ago

0 Minqiu Xie over 3 years ago

TI__Mastermind 21565 points

Hi Chase:

Thanks for reaching out. We will check your circuit soon.

0 Chase Jeong over 3 years ago in reply to Minqiu Xie

Genius 5060 points

Hi Minqui,

Thanks for the review, please let me know after checking this issue.

Best regards,

Chase

0 Yichen Xu over 3 years ago in reply to Chase Jeong

TI__Expert 4760 points

Hi Chase,

The circuit can be simulated using PSpice model in the hyberlink you inserted.

The result is as below(I think you switched the results):

apply voltage to VBUS_MOD=0V --> VBUS=4.95V

apply voltage to VBUS_MOD=2.8V --> VBUS=0.56V

leave VBUS_MOD as floating --> VBUS=4.17V

It is Ok to use the device this way but the PG pin requires pullup resistor connecting to any voltage rail less than 5.5 V. You can connect it to Vout with a 1MΩ resistor.

Best Regards,

Yichen Xu

0 Chase Jeong over 3 years ago in reply to Yichen Xu

Genius 5060 points

Hi Yichen,

Thank you for the review.

actually PG in is already have 100K pullup resistor with 3.3V MCU supply voltage. is it okay to use the device?

or changing 1M pullup resistor to Vout as you said is better?

Best regards,

Chase

0 Yichen Xu over 3 years ago in reply to Chase Jeong

TI__Expert 4760 points

Hi Chase,

It is Ok to set PG pin in this way. By the way, why do you use 5 resistor to achieve adjustable output voltage? It seems a little complex and the current consumption is large on R9 and R15 when VBUS_MOD=2.8V.

Best Regards,

Yichen Xu

0 Chase Jeong over 3 years ago in reply to Yichen Xu

Genius 5060 points

Hi Yichen,

Thank you for your reply,

I agree that the schematic is little complicated, just my partner designed for us.

can you suggest the best way to get a same VBUS result without R9 and R15?

we have a very busy time now, but we can apply your suggestion on next sample.

and i have one more question, could you send me the PSpice simulation project files through my personal email?

it can be very helpful to us.

Best regards,

Chase

0 Minqiu Xie over 3 years ago in reply to Chase Jeong

TI__Mastermind 21565 points

Thank you, Yichen!

Hi Chase:

May I know why you change the Vout? How do you care about the precise?

For Vout=0.5V. Actually, we won't recommend to operate with such low Vout for TPS63050.

0 Minqiu Xie over 3 years ago in reply to Minqiu Xie

TI__Mastermind 21565 points

Hi Chase:

May I know is there any update?

0 Chase Jeong over 3 years ago in reply to Minqiu Xie

Genius 5060 points

Hi Minqui,

Sorry for the late reply.

We want to create PLC(Power Lone Communication) signal using TPS63050, because the PCB is too small to add more schematics for PLC.

anyway there are 2 questions about this schematic.

1. my partner gave us this schematics and the result is good so far, but we don't know know exactly how it works. can you explain this?

(ex; when applying 2.8V on VBUS_MOD, VREG_FB and FB pin become ??V because of dividing resistors and it makes VBUS to 0.5V... and something)

2. last time you said that the current consumption on R9 and R15 is large, and the schematic is little complex.

could you recommend more simple way to get same results? (by removing some resistors)

Please check those issues. Thanks.

Best regards,

Chase

0 Yichen Xu over 3 years ago in reply to Chase Jeong

TI__Expert 4760 points

Hi Chase,

The circuit can be regarded as below

Vo and VBUS_MOD are two separate voltage source for VFB. The current through FB line can be ignored. And Superposition theorem can be used be calculate this circuit. This means, VFB are composed by two parts, on of them(VFB1) is supplied by Vo while the other(VFB2) is supplied by VBUS_MOD. When calculating VFB1, VBUS_MOD should be regarded as short circuit and vise versa. For example, VFB1=Vo*(R9||R15+R5)/(R9||R15+R5+R1). Because VFB is constant 0.8V, you can use VFB1+VFB2=VFB to calculate Vo.

And for simpler resistor design, you can take the link below as reference. If VBUS_MOD is a DAC output, 3 resistors should be enough if you need 3 output voltages. But 2 output voltages would be easier to design.

https://www.ti.com/lit/an/slva251/slva251.pdf?ts=1603785227318&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS63050

Best Regards,

Yichen Xu

0 Yichen Xu over 3 years ago in reply to Chase Jeong

TI__Expert 4760 points

Hi Chase.

The simulation model can be downloaded here

https://www.ti.com/product/TPS63050?keyMatch=TPS63050&tisearch=Search-EN-everything&usecase=GPN

Best Regards,

Yichen Xu

0 Chase Jeong over 3 years ago in reply to Yichen Xu

Genius 5060 points

Hi Yichen,

I saw the document below which you noticed me;

https://www.ti.com/lit/an/slva251/slva251.pdf?ts=1603785227318&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS63050

I can see only 2 output options, VOUT_LOW and VOUT_HI. also there are also 2 variables, VDAC_LOW and VDAC_HI.

i think this means it can make 2 different outputs with 3 resistors, and i cannot see the explain to make 3 different outputs for our purpose.

could you explain it more how can I design the resistors for 3 outputs?

Best regards,

Chase

0 Yichen Xu over 3 years ago in reply to Chase Jeong

TI__Expert 4760 points

Hi Chase,

In the document, it is easy to know that VFB=Vout*(R2||R3)/(R1+R2||R3)+VDAC*(R1||R2)/(R3+R1||R2). Once you have designed the value of R1, R2 and R3(using the values in the document as example), you can calculate a VDAC if you need another Vout. For example, if you need 2.5V Vout, VDAC should be 1.875V. In fact, if the pin support DAC rather than just 1 and 0, you can get many output as you desired.

Best Regards,

Yichen Xu

0 Minqiu Xie over 3 years ago in reply to Yichen Xu

TI__Mastermind 21565 points

Hi Chase:

As long time no hear from you, I assume you have solved the issue. If not, just reply below. Thank you!

0 Chase Jeong over 3 years ago in reply to Minqiu Xie

Genius 5060 points

Hi Minqui,

finally we checked this schematic all. and we decided to use this circuit.

Thank you for your help.

Best regards,

Chase

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TPS63050: Can I apply voltage directly to VBUS pin through resistor?