TPS61175: Is there a programmable boost converter solution

Hi, Helen. My bad; I should have specified those parameters.

Vin: micro USB 5V (4.7~5V)

Vout: I wish to control this using my MSP432 MCU via SPI, I2C, UART.

The range is 15~30V.

Iout Max: 0.1A

- So I was thinking of using the TPS61175 with a digital potentiometer TPL0501-100.

- Or hoping to use an alternative boost converter solution from TI

- Just like TPS61175, I wish to use the ENABLE pin toggling feature. I want to use MSP432's GPIO to turn it on/off.

- The size/price of the boost converter doesn't really matter.

- I do not care about the boost converter's efficiency, but I hope this dissipates low heat (50 °C or less) as possible.

- But I do not prefer Ball Grid Array packages.

Q0. What will be your suggestions?

Q1.

Helen chen said:

For the boost converter, we can change the Vout by injecting a voltage into the FB pin.

I never heard of this. May I ask more details about this, please?

Wow, Helen. This is truly interesting!

Helen chen said:

You can refer to the below sch for a reference, the concept is the same.

Q0. Do you mean to create a schematic like this?

I referred your design and the WEBENCH design as well.

Q1. In your picture, I don't see Rp2. Can you re-arrange your equation, please?

I think this is terrific, Helen! Just a few more things, please.

I think the concept is to use the superposition of voltages to control V_FB.

However, in that example, it uses the LED's current to calculate V_RS.

Whereas for my case, I don't know what value should I set for V_RS and R_RS.

So my questions are

Q0. Since my case is a little bit different, how should I set R_RS and V_RS?

Q1. For my case, should I set VOUT1 = 30.50V for PWM 0% duty cycle and VOUT2 = 3.6V for PWM 100% duty cycle?

Or the opposite, VOUT1 = 3.6V and VOUT2 = 30.50V?

Q2. In equation 1, it says "VFB is the TPS61021’s feedback regulation voltage (VFB=0.795V). "

Does this mean VFB, for both TPS61021 and TPS61175, is constant or fixed?

If not, I wish to know VFB was calculated.

After this, I think I will be able to calculate

R1, R2, R3 using Excel

https://www.hec.ca/en/cams/help/topics/Solving_equations_with_Excel.pdf

Thanks for everything.

P.S.) I haven't received your reply from my other thread.

I hope you can take a look Helen, please.

Dear Helen.

Helen chen said:

You just need to consider the LED currents is 0.

I see. However, I'm still having trouble how to set the values. Because for equation 1, the LED 1 is on so I think there are other considerations.

Q0. Since my case is a little bit different, how should I set R_RS and V_RS?

Q1. For my case, should I set VOUT1 = 30.50V for PWM 0% duty cycle and VOUT2 = 3.6V for PWM 100% duty cycle?

Or the opposite, VOUT1 = 3.6V and VOUT2 = 30.50V?

Q2. In equation 1, it says "VFB is the TPS61021’s feedback regulation voltage (VFB=0.795V). "

Does this mean VFB, for both TPS61021 and TPS61175, is constant or fixed?

If not, I wish to know VFB was calculated.

Thanks.

Helen chen said:

Vout1 and Vout2 is your two target output voltage.

Q0. My desired range is 3.6 ~ 30.50V. Should I set VOUT1 = 30.50V for PWM 0% duty cycle and VOUT2 = 3.6V for PWM 100% duty cycle?

Or the opposite, VOUT1 = 3.6V and VOUT2 = 30.50V?

Q1. How should I set R_RS and V_RS?

Helen chen said:

What is your Vin? Vin should be <Vout1=3.6V. or you need to use Sepic instead of Boost.

I wish to make a correction for my previous input.

My desired VOUT range is 6 ~ 30.50V.

The Vin is 5V by using the micro USB. How should I set R_RS and V_RS for this case?

Thanks, Helen! I did some math.

After referring the WEBENCH design, I fixed R1 (RFBT) to 392k Ohm. I also used the equations from the reference design PMP15037.

By setting VOUT1 (0% PWM, max voltage) = 31V and VOUT2 (100% PWM, min voltage) = 6.5V, I got

R2 (RFBB) = 23.55964641 k Ohm

R3 = 51.68 k Ohm

By choosing

R2 = 23.7 k Ohm

R3 = 51.7 k Ohm

I expect to get VOUT as 6.38477145 ~ 30.87529369 V.

I have 3 questions left before closing this.

Q0. Is my calculation and schematic connection correct?

Q1. I can use the boost converter TPS61175 for this, not the Sepic, right?

Q2. I have the TI's dac7760 DAC chip on my custom PCB. Instead using PWM and the low pass filter, which was connected to R3 for PMP15037,
can I connect a DAC output instead to R3, just like my schematic?