TPS51200: Worst case tolerance on VO

Akhil K A33

Part Number: TPS51200

Hi Team,

I want to calculate the worst case total tolerance on VO.

In my circuit 1.39V with 1.6% tolerance is applied to VLDOIN. Half of same voltage is applied to REFIN input using two 10K resistors with 3% total tolerance.

These two tolerances causes a +/-21mV deviation in REFIN voltage itself.

VOSNS has +/-15mV tolerance, REFOUT voltage tolerance to VREFIN is +/-12mV, then total tolerance on VO is 48mV.

This actually violating the JEDEC standard "VTTREF – 40 mV < VTT < VTTREF + 40 mV".

Also max. recommended DC operating VTT voltage for DDR3 in my application ( IS46TR16640CL) is from 0.642V to 0.725V. But the calculated max. voltage on VO pin is 0.7423V which exceeding the max. rated value.

Please help to resolve this issue as soon as possible.

Thanks

Akhil

over 1 year ago

0 Matt Sunna over 1 year ago

TI__Guru* 81035 points

Hi Akhil,

I have assigned this to someone on our team to look into, but I wanted to share these previous similar threads in case they are helpful:

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/996593/tps51200-what-is-the-maximum-tolerance-of-tps51200-vo-terminal-output-voltage/3683997

https://e2e.ti.com/support/power-management-group/power-management---internal/f/power-management---internal-forum/1024118/tps51200-large-variation-of-vtt-vo-issue/3791050

https://e2e.ti.com/support/power-management-group/power-management---internal/f/power-management---internal-forum/99524/tps51200-ddr3-application---jedec-compliance/349913

https://e2e.ti.com/support/power-management-group/power-management---internal/f/power-management---internal-forum/131604/tps51200-vo-refout-accuracy-versus-resistor-divider-at-refin-tolerances/477246

Best regards,

Matt

0 Akhil K A33 over 1 year ago in reply to Matt Sunna

Prodigy 160 points

Hi Matt,

Thank you for the quick support.

Except first thread, all other pages are not found.

I need to consider the tolerance of input voltage and resistors which is not mentioned in the above thread.

Thanks

Akhil

0 James Steenbock over 1 year ago in reply to Akhil K A33

TI__Mastermind 22365 points

Hi Akhil,

The TPS51200 spec states that Vo has a tolerance of +/-25mV to REFOUT and REFOUT has a tolerance of +/-12mV to REFIN. Together this amounts to +/-37mV total tolerance, and this would be worst case.

VTT and VTTREF are linked by these specs so that you should not see VTT and VTTREF violate the JEDEC requirements. If the input voltage to the IC pins has already deviated from the expected voltage due to external component tolerance and power supply error, this doesn't seem to indicated an issue with the TPS52100 as much as an issue with the voltage supply. Depending on what you feed the IC, the outputs should still follow the spec.

Depending on the resistors and power supply, it seems that tolerance calculations can vary widely, so there's not much I can recommend besides using tight tolerance components and running the calculations as necessary to see if the components will provide accurate voltage to the TPS51200 input pins. The last thread in the above list indicates that 1% tolerance resistors should be enough (this was used for our EVM board).

Also, can you share the datasheet for the IS46TR16640CL that you are using and let me know where you are seeing the max voltage spec for VTT? I took a look myself but I didn't see mention of these max voltages. Are they being calculated from a different spec?

Regards,

James

0 Akhil K A33 over 1 year ago in reply to James Steenbock

Prodigy 160 points

Hi James,

Thank you for your support.

Please see below the Recommended DC Operating Conditions of VDDQ for IS46TR16640CL. VTT = VDDQ/2. From this I took max. recommended DC operating VTT voltage as 0.725V.

Regards,

Akhil

0 James Steenbock over 1 year ago in reply to Akhil K A33

TI__Mastermind 22365 points

Hi Akhil,

Akhil K A33 said:
Also max. recommended DC operating VTT voltage for DDR3 in my application ( IS46TR16640CL) is from 0.642V to 0.725V

Just to clarify, in the original post you mentioned DDR3 which would be VDDQ = 1.5V and VTT = 0.75V (Typical) according to the above picture, but in the image you shared and in your calculations you are taking the voltage specs for DDR3L which uses a lower voltage.

If your application is using DDR3, I would recommend using 1.5V from VDDQ (0.75V VTT). This would fall in line with the DDR3 spec shown above. If you are actually using DDR3L, then your target should be 1.35V VDDQ (0.675V VTT).

Regards,

James

0 Akhil K A33 over 1 year ago in reply to James Steenbock

Prodigy 160 points

Hi James,

Actually I am using DDR3L for DSP ADSP-21593. As per DSP datasheet, recommended DDR3L Controller Supply Voltage is as follows:

That is why I am using 1.39V instead of 1.35V.

Regards,

Akhil

0 James Steenbock over 1 year ago in reply to Akhil K A33

TI__Mastermind 22365 points

Hi Akhil,

If we assume that you are able to apply 0.695V (1.39V / 2) directly to the REFIN pin and we take the REFOUT tolerance of +/-12mV, that means worst case positive deviation would cause REFOUT to be 0.707V. From there we can take the tolerance of VO with respect to REFOUT as +/-15mV. Worst case positive deviation would cause VO to be 0.722V.

Even with both tolerances at worst case (and VDDQ above the recommended 1.35V), your VTT should still fall within the max spec of the IS46TR16640CL. There will be some external factors such as resistor tolerance and supply accuracy that will affect you ability to provide exactly 1.39V VDDQ and 0.695V REFIN, so you would need to figure out your VDDQ range before assessing whether the TPS51200 will be outputting the necessary voltage.

Regards,

James

0 Akhil K A33 over 1 year ago in reply to James Steenbock

Prodigy 160 points

Hi James,

The worst case VDDQ voltage range in my circuit is as follows:

Min - 1.3674V, Typ - 1.3888V, Max - 1.4113V

So VDDQ voltage is within recommended range of both DDR3L and DSP.

Considering max. VDDQ voltage1.4113V and two voltage divider 10K resistors with 3% total tolerance at REFIN, then max REFIN input voltage will be 0.7153V (performed Monte Carlo analysis). Then adding total VO tolerance of 27mV gives 0.7423V which exceeding the max. VTT rated value of 0.725V.

Regards,

Akhil

0 James Steenbock over 1 year ago in reply to Akhil K A33

TI__Mastermind 22365 points

Hi Akhil,

If the max voltage of your system is causing the spec to be exceeded then you would need to either adjust the resistor tolerance or lower the input voltage.

Regards,

James

0 Akhil K A33 over 1 year ago in reply to James Steenbock

Prodigy 160 points

Hi James

Thank you for the support.

Regards,

Akhil

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TPS51200: Worst case tolerance on VO