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TPS63070 DaughterBoard

This board is based on the TI TPS63070 which is a buck-boost converter chip. It boosts a high range of voltages to 3.3V or 5V.

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The goal was to boost a Li battery voltage from 3-4.2V to a usable 3.3V or 5V. Since 3V is smaller than 3.3V and 4.2V is higher I need a buck-boost chip. The size was also a constraint.
The TPS63070 can ouput up to 2A. The circuit is based on the example shown in the datasheet.
Both the schematic and the PCB were made in KiCad 5.0.

The selection of the feedback resistors is critical.

 The standard output voltage is supposed to be 3.3V. For the appropriate resistor values i just checked the datasheet which had a table with values.

Since the I want to be able to select the output voltage I need to work out the R3 resistor value. When VSEL is high FB2 is connected to GND thus changing the feedback voltage divider and the output voltage.

The equation for R3 can also be found in the datasheet:

R3= \frac{Vo1\cdot R1\cdot R2^2}{\left(Vo2-Vo1\right)\cdot\left(R1 \cdot R2 +R2 ^2\right)}

\frac{3.3\cdot470\cdot150^2}{\left(5-3.3\right)\cdot\left(470\cdot150+150^2\right)}

Therefor R3 ~ 221kΩ

The final values are:

Vo1Vo2R1R2R3
3.3V5V470 kΩ 150 kΩ221 kΩ

Inductor selection

Since I already know I want to use a 1.5uH inductor, the peak current is a main factor. Again the datasheet helps us with an equation. First we have to calculate the boost duty cycle:

D=\frac{Vout-Vin}{Vin}=\frac{5-2.8}{2.8}=0.7857142857

Vout is set to 5V, the max output voltage that will occur. To be sure I set the minimum input voltage to 2.8V.

Now finally we can figure out what current we are working with:

\frac{Iout}{ \eta\cdot\left(1-D\right)}+\frac{Vin\cdot D}{2\cdot f\cdot L}=\frac{2000}{0.9\cdot\left(1-0.7857142857\right)}+\frac{2.8\cdot0.7857142857}{2\cdot2.4\cdot1.5}

                                                                           = 10370.67593mA

That is allot of current! Maybe I will not be able to put 2A through this at 2.8V in and 5V out. but a Lipo at 2.8V or 3V will not output 2A anyway. Let's use some more realistic values.

VinVoutIpeakIoutη
2.8V5V10370.67593mA2A0.9
3.0V5V6666.925927mA2A0.9
3.0V5V3333.592593mA1A0.9

I feel confident with a inductor that can handle 4A.

Now let's choose a suitable inductor. The site I am sourcing almost all my components from is Lcsc.com.They provide allot of components at low prices. Sadly they don't have the TPS63070 yet so I have get that somewhere else. Back to the inductor: I need a SMD inductor that can handle 4A at 1.5uH and has the lowest possible DC Resistance for a decent price. I chose the FDSD0630-H-1R5N=P3 from Murata with a rated current  of 8.5A and 13mOhm DCR for ~ 0.37$.

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  • First Prototype

    Jon Random04/24/2019 at 20:07 0 comments

    The first board revision with it's components arrived last week. After a quick inspection I started soldering the QFN-Chip on to the PCB. Since I use lead free solder it was a bit harder, but still possible.

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Discussions

David Wilson wrote 01/07/2021 at 22:46 point

Promising start--are you still working on this? I'm wondering how it worked.

  Are you sure? yes | no

liklev wrote 03/05/2020 at 21:26 point

Hi Jon Random, regarding TPS63070, is it going automatically from boost to buck mode?

With TPS63060 mentioned this features, but not with 70.

I mean if supply voltage not stable (bicycle hub dynamo).

  Are you sure? yes | no

Jon Random wrote 03/05/2020 at 21:37 point

Hi, as far as I know it does switch automatically and fluidly.

  Are you sure? yes | no

liklev wrote 03/06/2020 at 18:30 point

thanx, by the way there are available evaulation modules for these chips:

https://www.digikey.com/catalog/en/partgroup/tps63070-evaluation-module/65111

but a bit oversize to accomodate extra pin heads for experimenting.

  Are you sure? yes | no

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