TPS61288: Same input and same output

Hi zuhaib,

When input is close to output, the device will trig minimum on time limitation.

The output ripple will become very large at heavy load.

there are two stages,

1. voltage rising due to the minimum on time

2. voltage drop due to the output higher than target.

Unless you have very large output capacitance at output side, it is not recommended to work in this condition, especially heavy load.

Best Regards

Fergus

Thanks for your response ,Please let me know what will be the maximum input we can give for stable 12V output boost.

Also please let me know the the difference we have to maintain between input and output.

thanks

Thanks for your quick response .

Okay then I think this IC will not be suitable for my application.

My application is to use 11.1 V lithium battery .

Its lower voltage is 9V and HIgher is 12.6V.

and I want a stable output at 12V can you please help me in finding the suitable ic for my application in low cost.

thanks ..

Hi zuhaib,

How about using buck-boost converter?

Could you please provide your output current?

You can have a look at TPS552892 and TPS55165-Q1.

Best Regards

Fergus

I find two parts 

1.TPS55289

2.TPS552892

both are similar with some feature difference 

I cant find TPS552892 in webench simulation so I used TPS55289 Instead.

When I set Vin min 12.6V Vin max=12.6 V Ioutmax=1.5 amp

12.2V Vin max=12.2 V Ioutmax=above 5amps

13V Vin max=13 V Ioutmax=above 5amps

Why is this behaviour then I was checking the Iout max in my voltage range and what I found out is When the input voltage is 12.3V to 12.9V

Iout max is limited to 1.5 ampere.

When is voltage is equal to or less than 12.2 and 13V or above then only Iout max is around 5 amps .

why is it so? and how to resolve this issue 

thanks

Hi zuhaib,

I didn't find such questions like yours.

Maybe your design is restricted by frequency and power loss?

please refer to this,

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=F421249F1A77FA97

Best regards

Fergus

Yes if you put the range it will show Imax above 1.5

but to get a practical idea when the voltage range comes to 12.3 to 12.9 Imax is limited to 1.5 you can check it by yourself by giving Vin and Vmax same at input .

Now when I connect a lithium battery at the input And my battery is charged to 12.6V and the output voltage is 12V . the current in this scenario will be 1.5 amp only Until the voltage falls below or equal to 12.2 V . 

kindly verify this at your end as you should have some other resources to test this as well.

And I am also amazed by your quick responses hope to get the same in future as it will ease my IC selection.

thanks

Hi zuhaib,

I'm a little confused that whether you are describing the bugs of Webench or the profiles of your design.

The Webench simulation may have some bugs here and I think TPS552892 is fit for the case.

Also, you can use the Pspise model and calculation tool to verify your design.

It is recommended that you have a clear description of your own design like input and output.

I will loop expert of TPS55289 to follow up your questions.

Best Regards

Fergus

Can you ensure me that in the range of Vin 9V to 12.6V I will get stable 12V and the I max will not be reduced too much then I can proceed

Hi Zuhaib,

What is the max output current you need? 

I want 12V/2.5 amps at output

Hi Zuhaib,

Ok, then TPS552892 is suitable for your application if no I2C function is needed. If you need I2C programming, you can choose TPS55289.

May I ask what application and product type of this project? Would you like automotive version?

I have a power supply which generates 12.6v/2.5 amp and battery backup of 11.V lithium battery pack boosted to 12V when both present 12.6 and 12v are connected together so device is powered with mains when there is an outage 12V will be there and system runs on battery .

Our application is to run IOT GATEWAY with charger 12.6v/2.5 amp and 12V/2.5 On battery.

Hello Bryce ,

Can you please help me in selecting inductor and comp pin components as well the calculations look quite complex in the datasheet do you have   some calculators for that and if not you can directly suggest me the values and ratings of the components .

thanks 

Hi Zuhaib,

Thanks for feedback.

I am still confused, will 12.6V and 12V be connected together? Do you have any block diagram about that? 

Please see attached TPS552892 calculation tool, if no I2C is used, you can use TPS552892.

And you can post the schematic here when you finished, so I can check it for you.

0842.TPS552892 Design Calculation V1.0.xlsx

Regards,

Bryce

Hello bryce can you please share the same tool for TPS61288.

Yes surely I will upload the schematic for your reference once completed ,I will let you know.

Hi Zuhaib,

Please see below TPS61288 calculation tool.

https://www.ti.com/lit/zip/slvrbh4

Regards,

Byce

Hello bryce this is the result after I have given input as 2.8-4.2 V .

Vout =5V 2.5 Amp

calculated effective output capacitance is shown 49.60. but selected effective is 100uf .Then what I have to use.

Please also let me know the inductor value and current I have to use ,please directly suggest me the values and I will incorporate it in my design and complete the schematic,Once done i will also share the layout with you for review.

Hi Zuhaib,

The effective value is the actual value you use, it needs to be larger than calculated to ensure ripple.

It looks that TPS61288 is over design in your case. TPS61022 is recommended in this case.

Best Regards

Fergus

Can you please let me know why are you saying that the it is overdesign?

what factors are out of specified limits of IC please let me know

Hi Zuhaib,

for input 2.8-4.2 V and output 5V 2.5 A, the inductor current shall be about 5A peak,

TPS61288 has a peak current of 15A and a maximum output voltage of 18V.

So, I said it is overdesigned.

You can choose TPS61022 with smaller size and disconnect function in this case.

Best Regards

Fergus

first please let me know if peak current of my design is 5 A and max of IC is 15 amp mine is already less so how it is overdesigned please explain . 
also please let me know what is the minimum input I have to give and what is the maximum current I can take from output at 5V ,so that the design is not overdesined . 
please expain in detail as I am already in designing stage

Hey bryce can you please look into the matter I have attached my design file . Fergus is saying it is overdesign Please help

Hi Zuhaib,

According to your application requirement, I agree with Fergus's words. TPS61288 and TPS61022 are both ok. But TPS61022 is more suitable because the current limit of TPS61288 is too large which will need you to choose inductor with higher saturation current, so the size and cost will also increase.

Regards,

Bryce

Actually I will be using this same IC for boosting 12 V at VIN 8.4-12.6 as well.

That is why I am using this IC so that we can order once in bulk for the other design as well.

By your suggestion I will test TPS61022 As well.

Meanwhile please suggest me the inductor And please verify other components and their values too and please let me know.

thanks and regards

Hi Zuhaib,

Double confirm, will you use TPS61288 with Vin 8.4-12.6 and Vout 12V? This device is not suitable. Recommend TPS552892 as we talked above.

sorry By mistake I wrote 12.6V it was 8.4v only to 12V out .

Lets just focus on for input 2.8-4.2 V and output 5V 2.5 A

Please suggest Inductor and other values for my design.

thanks

Hello Bryce can you please review my schematic and suggest me the inductor value or part with current and also other components if needed. Please...

thanks

Hi Zuhaib,

Here are my comments.

1. Recommend to choose inductor with higher saturation current, the Isat of the current  is too small. It should be higher than the peak current limit is 15A.

2. I see 1000uF at the output side, so recommend to change R9 from 9k to 100k to obtain higher phase margin.

3. Recommend to add one 0.1uF cap at the output side, and put it close to Vout and GND pin at PCB layout.

BRs,

Bryce

Hello Bryce thanks for your comment,

Inductor selection always becomes a tough task for me can you please suggest some part number for my reference with the desired current and inductance value please.