TPS51916: Switching frequency and D-CAP

Evgeniy Sokolov

Part Number: TPS51916

Hello TI Experts,

1. Please tell me why is the ability to change the switching frequency of the TPS51916? When can I need her? And how to determine which switching frequency is necessary for my processor and RAM?

2. Which version of D-CAP is better than 1 or 2 and why?

over 5 years ago

0 Qian Chen over 5 years ago

TI__Mastermind 24075 points

Hi Evgeniy,

1. With higher switching frequency, you can use small inductance, but the switching loss will be higher.
2. I suggest to use DCAP2 because it works with ceramic output cap.

As the start, I suggest to select DCAP2 with 500kHz switching frequency.

Thanks
Qian

0 Evgeniy Sokolov over 5 years ago in reply to Qian Chen

Intellectual 630 points

1. That is, dc-dc buck (step-down) convertors, for example, with a switching frequency of 1.5MHz are not suitable for generating VDDQ for DDR3?
2. Accepted.

New question:
3. Is it possible and better to use LDO to generate voltage?

0 Qian Chen over 5 years ago in reply to Evgeniy Sokolov

TI__Mastermind 24075 points

1. The switching loss will be very high with 1.5MHz switching frequency.
3. LDO efficiency is very poor. It is not recommended.

Thanks
Qian

0 Evgeniy Sokolov over 5 years ago in reply to Qian Chen

Intellectual 630 points

1. What will be the losses? You can describe in more detail the process of the origin of the losses.
3. Accepted.

0 Qian Chen over 5 years ago in reply to Evgeniy Sokolov

TI__Mastermind 24075 points

Hello,

The switching loss is basic knowledge for power supply.
I would suggest you to search "switching loss" and find some material to understand how switching loss comes from.
Sorry about it.

Thanks
Qian

0 Evgeniy Sokolov over 5 years ago in reply to Qian Chen

Intellectual 630 points

Hello Qian,

1. Do I need to use tracking or not with TPS51916? Why do I need a "tracking" I do not understand the meaning of its use Explain please.
2. At the moment it is a very multifunctional regulator, since I do not need the completion and availability of VTT for this. Perhaps you would recommend a simpler controller to generate only one VDDQ with the above mentioned, so that there are no problems with filling and losses when switching. I use only 1 DDR3 memory module located close to the processor.

0 Qian Chen over 5 years ago in reply to Evgeniy Sokolov

TI__Mastermind 24075 points

HI Evgeniy,

What's Vin voltage in your application, 12V?
DDR3 needs VTT voltage, why do you not need VTT voltage?

Thanks
Qian

0 Evgeniy Sokolov over 5 years ago in reply to Qian Chen

Intellectual 630 points

VTT is required to complete DDR3 signals with line lengths> 50mm (Micron). I use one unbuffered DDR3-1066 module (256x16) and the length of the signal lines is less than 50mm. I only need VDDQ, because I get the VREF with a divider of two resistors. input voltage (VIN) I have 5V.

0 Qian Chen over 5 years ago in reply to Evgeniy Sokolov

TI__Mastermind 24075 points

Hello,

You application just need a 5Vin, 1.5Vout small current regulator.

Can you use TI power designer to search other parts?
webench.ti.com/.../switching-regulator

If you have question on any other part, please submit a new post with the part number. Some other TIer will support.

Thanks
Qian

0 Evgeniy Sokolov over 5 years ago in reply to Qian Chen

Intellectual 630 points

Hello Qian,
How can I choose a suitable component if I do not know what the permissible switching frequency for DDR3 and the number of switching losses? Please advise the frequency of the dc-dc converter and the allowable switching losses that are optimal for working with DDR3 or suggest a component suitable for generating VDDQ (1.5V) for 1 DDR3 memory module.
Thank you.

0 Qian Chen over 5 years ago in reply to Evgeniy Sokolov

TI__Mastermind 24075 points

Hi Evgeniy,

The switching frequency and switching loss is for power converter, not for DDR3.
DDR3 just needs a stable VDDQ (1.5V) voltage. DDR3 does not has requirement on the converter switching frequency and switching loss.

TI power designer will select solutions for your application. It also will select switching frequency for particular part and create schematic. Please try it.
webench.ti.com/.../switching-regulator

Thanks
Qian

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TPS51916: Switching frequency and D-CAP