LP8733: need clarification regarding circuit design

shubhangi bagal

Part Number: LP8733
Other Parts Discussed in Thread: TIDA-050038

Tool/software:

What voltage level should I2C signals be pulled-up to? what are these signals referring to internally? in my design the signals are 3.3V rated. Do I need to level translate them to connect to LP8733?

VIO is not mentioned anywhere else in datasheet.

VANA in my design is 5V

4 months ago

0 shubhangi bagal 4 months ago

Prodigy 170 points

also the only 1.8V available in my design is output of PMIC (LDO1 in LP8733) itself

0 Sarah Lao 4 months ago

TI__Genius 10797 points

Hi Shubhangi,

I2C pullups are typically pulled to 1.8V or 3.3V source that is always on while PMIC is on.
5V VANA will be too high and 1.8V output may not be sequenced in time.

A 3.3V pullup source will be fine for SDA and SCL lines.
Just note that for > 1.95 V , the I2C bus cannot support High-Speed Mode (3.4Hz).
All other speed modes will be fine with 3.3V :

Best Regards,
Sarah

0 shubhangi bagal 4 months ago in reply to Sarah Lao

Prodigy 170 points

I guess, I can put a resistor divider to divide 5V (connected to VIN and VANA) to 1.8V and use that for pull-ups. Is that ok?

0 Sarah Lao 4 months ago in reply to shubhangi bagal

TI__Genius 10797 points

Hi Shubhangi,

That should also be fine, since the I2C lines will not draw much current.
And if VANA is constantly a stable 5V, the divider should not be a problem.

Generally, if you have a 3.3 V rail available, this would be preferred.

Best regards,
Sarah

0 shubhangi bagal 4 months ago in reply to Sarah Lao

Prodigy 170 points

Thanks.

Another question about factory OTP programming and part ordering :

are below only the orderable parts? or Can I provide the OTP programming inputs?

i need particular voltage outputs and power on sequence.

0 shubhangi bagal 4 months ago in reply to shubhangi bagal

Prodigy 170 points

what are pre-programmed parameters above parts in above table?

0 Sarah Lao 4 months ago in reply to shubhangi bagal

TI__Genius 10797 points

Hi Shubhangi,

The parameters for the parts in the table above can be found in their respective Technical Reference Manuals here.

This device is not user-programmable. The potential for a custom factory-programmed OTP parts will need to be assessed based on business case.
Please reach out to your local marketing representative for more information.

Best Regards,
Sarah

0 shubhangi bagal 4 months ago in reply to Sarah Lao

Prodigy 170 points

Hi Sarah,

Thanks. This is really helpful.

(The links should have been provided in datasheet next to orderable parts in table. That would have saved me a lot of time.)

Based on these manuals LP87334E or 47 seem to be nearest fits. I will go through the manuals for both and get back if any questions.

Meanwhile I have a few questions related to the circuit:

What is Cpol?
In TIDA-050038 module, CPol is not being used ?
What is the purpose of 0.1uF after 22uF at Buk output?

Should the FB_B0 pin connect to at the output capacitor or near to target connection?

Thanks,

Shubhangi

0 shubhangi bagal 4 months ago in reply to shubhangi bagal

Prodigy 170 points

Cpol shown here in datasheet:

0 shubhangi bagal 4 months ago in reply to shubhangi bagal

Prodigy 170 points

Hi Sarah,

2 questions regarding the technical manual for LP87334E:

1. Can the OTP be reprogrammed on bench?

2. If not, How soon after power-up can I start programing using I2C? Do I have to wait for power good to be high and outputs to be stable?

My concerns are the voltage on Buck 1 is 0.05V higher than what my circuit needs (more than 5%). So I cant supply it before reprogramming it to 0.8V.

Also the power up sequence of this part does not suit my requirements.

If OTP can be reprogramme don bench, that would be the best case.

Thanks,
Shubhangi

0 shubhangi bagal 4 months ago in reply to shubhangi bagal

Prodigy 170 points

Does this mean 0.85V does not reach by load if I program in STBY mode using I2C?

0 Sarah Lao 4 months ago in reply to shubhangi bagal

TI__Genius 10797 points

Hi Shubhangi,

Thank you for the feedback. I will look into getting the TRMs linked in the LP8733 datasheet itself.

Regarding your circuit questions:

C_POL is the Point-of-Load capacitor. These are placed towards the load in the application.
In TIDA-050038, the C_POLs are placed near the processor, shown on the CPU page, not the PMIC page.
0.1 uF output capacitor serves as a decoupling capacitor to minimize noise
For remote voltage sensing, FB_B0 can be placed near the target connection (to the point of load), else, FB_B0 can be connected to the local output capacitor.

Regarding OTP questions:

OTP of this device cannot be reprogrammed on bench, device will reset to default OTP values upon power cycle.
After power up, you must wait 1.2 ms before attempting to write with I2C
It is possible to reprogram the device without it starting up by holding EN low while reprogramming.
To reprogram the device without the device powering onto the default values:
1. Supply VSYS
2. Hold EN low
3. Wait 1.2 ms and write the desired settings to the registers
4. Bring EN high
5. Device will start with the written settings.

Let me know if you have any questions regarding the process above or about the device in general.

Best Regards,
Sarah

0 shubhangi bagal 4 months ago in reply to Sarah Lao

Prodigy 170 points

Hello Sarah,

Thanks for your response.

Our main concern is that none of the devices match with our default output voltages and we have to program output voltages through I2C everytime we power up, which will be a big overhead.

Thanks,
Shubhangi

0 Sarah Lao 4 months ago in reply to shubhangi bagal

TI__Genius 10797 points

Hello Shubhangi,

Are you able to share the output voltages your system needs so I may see if there is a better match for your design?

Best Regards,
Sarah

0 shubhangi bagal 4 months ago in reply to Sarah Lao

Prodigy 170 points

Hi Sarah,

Due to various limitations of LP8733, we are considering to explore DCDCs and LDOs instead. One I select the parts, if I have any questions, I will get back to you.

Meanwhile, can you please suggest a regulator to generate +2.5 and -2.5V from 5V input? Output current requirement 100mA.

Thanks,
Shubhangi

0 shubhangi bagal 4 months ago in reply to shubhangi bagal

Prodigy 170 points

operating temp range required: -40 to 125C

0 Sarah Lao 4 months ago in reply to shubhangi bagal

TI__Genius 10797 points

HI Shubhangi,

Thank you for the update.

I only handle the PMIC products, so I may ask you to create a new thread under a specific part number to be redirected to the converter device expert for regulator recommendations.

Something like LM27762 may fit your needs here, but does not seem to fit the required operating temperature range.
Please create a new thread to be connected to the product line expert who may have a better recommendation.

Thank you!

Best Regards,
Sarah

0 shubhangi bagal 4 months ago in reply to shubhangi bagal

Prodigy 170 points

Hi Sarah,

Thanks for your support. Appreciate it!

Regards,
Shubhangi

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LP8733: need clarification regarding circuit design