Status: Unknown, document is kind of a mess and has been neglected

Past Owner: @Steven Wang @Allan Liu

Project Goal was to output 5V USB - 24V @0.25A

Initial idea: use the TPS61175 to boost 5V input to ~40V before using buck converters to drop voltage down to the required 5V, 12V, 18V, 24V.

Efficiency calculations assuming maximum power draw of 5V @ 2.5A

Use TPS61175 to boost 5Vin to 24V, assuming maximum current draw of 2.5A we can get a maximum of 12.5W of power, after boosting to 24V the new current drops to roughly 0.52A given by the equation P = I₁V₁ = I₂V₂ after rearranging and solving for I₂. Figure 1 of the TPS61175 datasheet tells us that we can expect an efficiency of roughly 80% meaning that Pout will be 10W.

Buck converting 24V @ 0.52A to 12V will give an output current of roughly 0.83A. Figure 2-3 of the MCP16331 datasheet states that this conversion will have 90% efficiency, giving a final output power of 9W. The total efficiency of this conversion from start to finish is 72%.

Buck converting 24V @ 0.52A to 18V will give an output current of roughly 0.56A. There is no direct curve showing the efficiency-Iout graph of this conversion, but using Figure 2-3 of the MCP16331 datasheet as a rough estimate gives an efficiency of roughly 86%, with a final power output of 8.6W and total efficiency of 69%.

5V output will be directly from the input, no conversion necessary.

24V output will be directly from the boost converter, no bucking necessary.

Note these values assume no loss from passive components, traces, and environment.

Proposed Component Selection:

TPS61175 Parts Summary:

L1 = 15uH TDK 15uH Isat 3.3A

R1 = 185.280kΩ (184kΩ standard value) Yageo 184kOhm 0603

R2 = 10kΩ Yageo 10kOhm 0603

R3 = 10kΩ Yageo 10kOhm 0603

R4 = 80kΩ Stackpole 80kOhm 0402 OR Yageo 80.6kOhm 0603

C1 = 4.7uF* Murata 4.7uF 50V 0805

C2 = 4.7uF* Murata 4.7uF 50V 0805

C3 = 47nF Murata 0.047uF (47nF) 50V 0603

C4 = 24nF Kyocera 0.024uF (24nF) 100V 0805

D1 = SS3P6L-M3/86A

*C1 was stated to be “a low value capacitor” by the previous project lead, C2 was calculated at 687nF; however, the datasheet (Page 15, final paragraph) states a 4.7uF capacitor is recommended for typical applications, and as 4.7uf>687nF, I defaulted to the datasheet’s recommendation.

MCP16331T-E/CH Parts Summary:

12V:

L1 = 56uH Murata 56uH Isat 1.24A

R1 = 140kΩ Yageo 140kOhm 0603

R2 = 10kΩ Yageo 10kOhm 0603

C1 = 4.7uF (Input capacitor) Murata 4.7uF 50V 0805

C2 = 20uF (Output capacitor) Samsung 22uF 16V 0805

C3 = 0.1uF (Boost Capacitor) Yageo 0.1uF 25V 0603

D1 = https://www.digikey.ca/en/products/detail/smc-diode-solutions/DSS14U/8341859 (Freewheeling diode)

D2 = https://www.digikey.ca/en/products/detail/onsemi/1n4148/458603 (Boost diode, try find SMC version) https://www.digikey.ca/en/products/detail/onsemi/MMSD914T1G/919706 ->SMC version

18V:

L1 = 75uH (standard value, calculated value is 78uH) Wurst 75uH Isat 2.2A

R1 = 215kΩ Yageo 215kOhm 0603

R2 = 10kΩ Yageo 10kOhm 0603

C1 = 4.7uF (Input capacitor) Murata 4.7uF 50V 0805

C2 = 20uF (Output capacitor) Samsung 22uF 25V 0805

C3 = 0.1uF (Boost Capacitor) Yageo 0.1uF 25V 0603

D1 = (Freewheeling diode)

D2 = (Boost diode, try find SMC version) → SMC Version

Other components:

Indicator LED = (Green)

Vin USB = - I imported footprint for this one

Connector =

Vout connectors = Female connectors

18Vout indicator LED current splitting = 10mOhm 0.3W 0603 and 22mOhm 0.3W 0603

12Vout indicator LED current splitting =

MCP16331T-E/CH Microchip Technology | Integrated Circuits (ICs) | DigiKey

Open

maybe use this one for all voltage conversion - 50V Max input, 24V max output adjustable, 500mA max output, 500kHz switching frequency up to 96% efficiency. Will do more research on this chip later today.

datasheet page 19 section 5.2 details how to configure feedback pin to adjust Vout.

Initial Requirements:

+5V USB - 24V @0.25A Boost Converter PCB -

• Boost Converter PCB !

• Output Voltage

  • Adjustable to these standard voltages:

    • 5V - servo motor

    • 12V - jetson board

    • 18V - ground station

    • 24V - motors

  • Allowing for voltages in between is fine, but getting to these values would be nice!

• Output Current

  • Targeting 0.25A Output minimum (says maximum in the Design requirements section) at all adjustable voltage values

    • The highest minimum output power of which will be 24V*0.25A=6W

  • Being able to handle higher output current than this is absolutely fine under the requirement that it doesn’t vastly increase cost or development time.

• Efficiency

  • The use case for this board is take output from a 120VAC Single Phase to 5V USB standard power converter and use that output as the input to this board

  • Looking at a standard wall adapter I see they can do 1-2.5 A of output current at 5V so with some basic math, 24V*0.25A=6W & 1A*5V=5W, so efficiency is a concern in this case

  • Anything above 80% efficiency will work for us, but the higher the better for our use case!

  • Previously using a synchronous buck converter was considered imperative due to efficiency concerns, but a decision matrix should be used to evaluate it’s necessity vs cost.

• Cost

  • We don’t want cost to gate this project’s progress. Evaluate efficiency and difficulty vs cost via decision matrixes!

  • There are no hard requirements.

• Timeline

  • In order for this board to be most useful we would like it all debugged and functional before competition in May 2023 such that it can be utilized for debugging at that time.

  • Beyond that soft requirement it is entirely up to you. Once the Asana is back, we will utilize that to track progress.

• Input Output Connectors:

  • Vin

    • Take a pick of USB-C or whatever other standard USB you want.

    • Only need +5V and GND pins, (presumably no ERC +D and -D pins)

  • Vout

    • XT60PW-F

    • PWR and GND

• Other Features:

  • Status LEDs for both Vin and Vout voltage rails

  • Since the output voltage is adjustable, an LED indication to the user roughly where their output voltage is would be nice.

  • Bonus if you’re feeling crazy is roughly indicating the output current and other states of the converter though this is far from a requirement

Documentation:

Overview

The purpose of this boost converter board is to allow users to have a sustained voltage output at various voltages from a USB port. This board is used in an outdoor application where a power supply is not accessible.

Design Requirement

The input voltage on the circuit will be 5V from a USB port and the output voltage will be 12V, 18V or 24V at a maximum of 24V at 0.25A to an XT60 port which is the port used commonly on drones. There will be two voltage output modes which the user can choose by toggling a button on the board. A LED light will be integrated to indicate the current output voltages. The total power dissipation will be under 6W.

Architecture

This board will include a USB-C connector for the input voltage source and an XT60 connector as an output to provide a constant output voltage.

The topology used to achieve a voltage increase from 5V to a max 24V is a step-up converter or boost converter. A basic boost topology is shown in fig. 1 below. When the switch is on, the inductor will charge up. Once the switch closes the voltage will increase rapidly as the inductor tries to maintain the same current. The current will go through the diode and go into the capacitor. As a result, the output voltage will be higher than the input voltage.

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figure 1: topology of a boost converter

IC selection

However, in order to control the exact voltage output, the duty cycle has to be controlled. To accurately control the switch (duty cycle), a switching regulator IC has to be selected for voltage regulation and PWM control. There are serval options have been considered:

As shown in Table 1 above, the cheaper and older options like MC34063A , even though it matches the required input and output voltage but do not reach the required efficiency. While the more efficient IC which is synchronized such as LT8471 will also meet all the requirements but comes at a high cost of $17.17.

On the other hand, the TPS61175 does have a wide enough input range between 2.9V - 18V and a maximum output of 40V. The max output current is at 0.5A which will provide enough current for this application. Also, the efficiency of the IC can reach a maximum of 87% which is more than the desired efficiency of 80%. Thus looking at TPS61175, it is the best IC that meets all the design requirements and costs at a reasonable price of $6.88 (Digikey). A sample boost converter circuit using this IC is shown below:

footprint

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Diode selection

A diode is used as the freewheeling or catches component has a load current level at which they transition from discontinuous conduction to continuous conduction. To achieve the required efficiency of the boost converter a Schottky diode is best for this application. This is because it has the lowest recovery time and recovery charge and lower voltage drop.

SS3P6L-M3/86A(Datasheet) is recommended to be used in this application because the reverse breakdown voltage is 60V which is over the requirement of 40V and power dissipation is more than Iout * Vd or 0.135W

Inductor selection

Since the max voltage output is 24V and the max current output is 0.25A. Based on these requirements the inductor value can be calculated from the current ripple equation

As a result, only 4.7μH and 5.1μH inductors are the only e24 inductor values that suffice the max current output requirement with Fs at 600MHz. The max output current for the 4.7μH inductor is 0.289A and 0.266A for the 4.7μH inductor.

The inductance value also is influenced by the inductor ripple current. This is recommended to be 30–40% of DC current. The equation for DC current is:

The Vout is 24V, Iout is 0.25A, Vin is 5V and the conversion efficiency is

The equation for calculating the inductor value is

To input into this application

The inductor value has to be greater than 2.095μH. However, if the inductor value is lower than 4.7 μH, the slope compensation may not be adequate, and the loop can be unstable. Since the datasheet recommends an inductor value of more than 4.7 μH, a 15μH inductor (CLF10060NIT) is selected for this application.

To check if the selected inductor matches the requirement, this formula is used

where ΔIL is the inductor current ripple. Using the second equation and the duty cycle is set to 0 for the worst scenario,

the inductor ripple current is1.082A

Resistor selection

The resistor values are chosen based on Vout. The equation below shows the calculation

It is recommended to choose R2 around 10kΩ. At 24V, R1 is equal to 926kΩ, and at 12V, R1 is equal to 438kΩ. Also, a 100Ω resistor is added to reduce noise coupling from the OUT to the FB pin through the feed forward capacitor.

A resistor also has to be selected to set the switching frequency. Since the Css selection table uses 1.2 MHz as the switching frequency, a resistor has to be selected based on this frequency. The table for showing resistor value for different frequencies is shown below

In order to have the switching frequency of 1.2 MHz, an 80kΩ is selected for this application.

Compensation Resistor selection (R3)

The resistor value is set to 10KΩ

Capacitor selection

Feed forward capacitor

C2 or feed forward capacitor is used for improving transient response and phase margin. It is selected based on the pole and zero frequency. The typical value for the zero frequency is between 1 kHz to 10 kHz. For high output voltage, the zero and pole are further apart which makes the feed forward capacitor very effective. The equation for finding zero and pole is

Soft Start Capacitor(Css)

A soft start capacitor clamps the internal reference voltage, which allows the output voltage to ramp up slowly. A table from the datasheet for the finding of the soft start capacitor is shown below

In this case, a 47nF capacitor is used for this application

Input And Output Capacitor (C1,C2)

Since the power source is from USB, a small value capacitor is selected to filter out high-frequency signal

Output Capacitor is used to meet output ripple and loop stability requirements. The ripple voltage is related to the capacitor’s capacitance and its equivalent series resistance (ESR). Assuming a capacitor with zero ESR, the minimum capacitance needed for a given ripple can be calculated by

Let voltage ripple to be 1%, the voltage ripple will be 0.24V.

Cout is 687nF. A footprint of 0603 capacitor is left on the PCB to test a value that will fit this application. Larger form factor capacitors (in 1206 size) have their self resonant frequencies in the range of the switching frequency.

Compensation Compasitor(C4)

The equation for compensation compasitor is

Various Voltage Output

Since the IC can only output one voltage, in order to have different voltages out, a linear regulator IC is used to convert 24 V output from the boost converter to the desired voltage output. For 18V output, 7818(mouser) is used and for 12V output, 7812(mouser) is used.

USB Port

USB gen 2 is used because it is very common and comes at a low cost. There is no size requirement nor weight requirement for this receptacle port.

port(datasheet)

footprint

update: USB A is switched to a micro USB port so that the cable is easily accessible

port datasheet