TPS51100: How to use

Hi Higa,

1. S3 and S5 should be pulled high externally to turn on VTTREF and VTT output. 

2. When VDDQSNS is below 1.5V, the VTTREF and VTT may not track VDDQSNS/2 well. 

Thanks

Qian

Hellow Qian-san

Thank you for your quickly reply.

I have an additional question about your advice in below.

Would you please give some advice again?

>2. When VDDQSNS is below 1.5V, the VTTREF and VTT may not track VDDQSNS/2 well. 

-> Is it possible to change VLDOIN to obtain VTT of 1.5V or less when VDDQSNS is 1.5V or less?

    We want get VTTout=0.4V to 1.3V tracked to VDDQSNS.

    The reason we set VLDOIN to 1.5V is to reduce the loss of (VLDOIN-VTTout) x Ivtt.

    We are considering with the following schematic.

Best regards.

Higa

Hi Higa, 

I found an EVM and did some test on EVM. 

VLDOIN is fixed at 1.5V. VTT current is 1.5A. 

At VDDQ=0.8V, VTT is 0.4V. The part works fine when VTT current changes from 0A to 2A. 

At VDDQ=2.6V, VTT is 1.3V at light load condition. When VTT current is 1.5A, VTT is 1.28V. When VTT current is 2A, VTT is around 1.12V. 

In summary, the circuit should work at light load condition, but VTT voltage will drop with load current when VDDQ is 2.6V. 

Thanks

Qian

Hello Qian-san

Thank you for your kindly support.

I have a question.

Why does the characteristic of VTT voltage with respect to Ivtt current become worse when VDDQSNS voltage becomes higher?

I understand that the regulation of VTT is better when VLDO is fixed at 1.5V.

Is this correct?

Best regards.

Higa

Hi Qian-san

I am sorry for my misunderstanding.

I understand that the regulation of VTT is worse when VLDO is fixed to 1.5V.

Finally, let me add another question.

What is the minimum drop voltage between VLDO and VTT?

My customer is worried that VTT can get 0.4V when VDDQSNS is 0.8V.

Best regards.

Higa

Higa-san,

The part works well when VDDQSNS is 0.8V and VTT is 0.4V. 

When VDDQSNS is 2.6V, due to small drop voltage between VDLO and VTT, the VTT decreases when load current increase. 

I don't know the minimum drop voltage between VDLO and VTT. 

If you can let me know the load current in customer's application, I can do some test on EVM to check the minimum drop voltage required. 

Thanks

Qian 

Hi Qian-san

I appreciate your prompt reply and cooperation.

Yes.I will confirm about maximum load current with my customer soon. 

Best regards.

Higa

Hi Qian -san

I confirmed the load current condition with the customer.

Also, some VLDOIN conditions have changed.

Initially my customer was considering VLDOIN = VDDQSNS, but VLDOIN was changed to fixed at 1.9V or 2.6V.

I heard that the reason for the change in the conditions is that the specifications of the source power supply connected to VLDOIN have changed.

The condition of VDDQSNS remains unchanged, 0.8V to 2.6V (variable).

The load current is 0A to 2A.

The measurement conditions are summarized below.

1. VLDOIN is 1.9V fixed. VDDQSNS is 0.8V to 2.6V. Ivtt is 0A to 2A.

2. VLDOIN is 2.6V fixed. VDDQSNS is 0.8V to 2.6V. Ivtt is 0A to 2A.

I would appreciate if you could make a measurement.

Best regards.

Higa.

Hi Higa, 

The part on EVM was damaged by mistake. 

I need to order some new parts for fix the board first. 

It will take some time, but I will keep you updated. 

Thanks

Qian

Hi Qian

There is no help for it.

I will wait for your contact.

Best regards.

Higa

Hi Qian-san

Do you have any update on TPS51100?

Could you tell me about a current status?

Best regards.

Higa

Hi Qian-san

Thank you for your support.

The summarized data is as follows,

If VLDOIN is less than 1.9V and VDDQSNS is higher than VLDOIN, higher load currents will tend to result in poor regulation of VTT.

Would you please tell me if you know the reason?

Is it because the influence of driving the FET on the source side increases as VLDOIN decreases?

I'm so sorry to ask you many times.

Best regards.

Higa

Higa-san, 

TPS51100 is a linear regulator, not switching regulator. 

Due to output impedance, Vout does drops when current increases. We see similar behavior on other linear regulator such as TPS51200. 

If customer wants tight regulation, probably they should consider switching regulator. 

Thanks

Qian

Hi Qian-san

Thank you for your reply.

I understand that TPS51100 is a one of linear regulator.

What I want to know is why VTT regulation is worse when VLDOIN is 1.5V than when VLODIN is 2.6V.

Could you please tell me if you know that reason?

Best regards.

Higa

Hi Qian-san

Do you have any update?

I am requested your answer from my customer.

My customer wants to know why VTT regulation is worse when VLDOIN is 1.5V than when VLODIN is 2.6V.

Could you please tell me about that?

Best regards.

Higa

Hi Higa, 

When VLDOIN is 1.5V, the output impedance is larger than VLODIN=2.6V, therefore VTT regulation is worse at load condition. 

Thanks

Qian