TLV733P-Q1: Recommend IC for STM32F105 ADC power

Wei,

Without knowing their circuit, I’m guessing that they are using button presses to connect resistors of various values to a divider to generate various input voltages to the ADC. If that’s the case, since there will be a limited number of buttons on the faceplate of the head unit (maybe 20 max), then they can probably set up a significant voltage difference between any two button-press conditions. I would expect 20mV to 50mV would be a practical minimum number.

Assuming the ADC has 0dB PSRR, 120uV of noise on the ADC supply would be well below the threshold where it could affect measurement of the resistor ladder.

So I think the TLV733-Q1 should be fine, unless their implementation is very different from what I assumed.

Hi Prakash,

Thank you for the insight. Yes. what you guessed about the circuit is correct. In its application note, ST recommend power source with low impedance for ADC. Does TLV733P-Q1 meet that requirement?

https://www.st.com/resource/en/application_note/cd00211314-how-to-get-the-best-adc-accuracy-in-stm32-microcontrollers-stmicroelectronics.pdf

What about the question about LP2951-Q1? Is it good for stepping down the voltage for TLV733P-Q1 input? Is it suitable for power supply for STM32F105?

If you can recommend a power scheme with 12 - 14V input from the vehicle to get power supplies for STM32F105, ADC circuits, TCAN1044ADRQ1, TLIN1021ADRQ1, deserializer like UB914/928 or UR908, it would be much appreciated.

So just use linear regulators? Should we also consider buck step down regulator? With STM32F105, ADC circuits, TCAN1044ADRQ1, TLIN1021ADRQ1, and deserializer like UB914/928 or UR908, also we need power for LED backlight for buttons, I believe we also need something with higher current support. Please advise.

Wei,

I have added our Systems engineer to comment here.

Thanks,

Prakash L

Hi Wei,

            Could you share a schematic showing the signal flow and the voltage/current rating needed for each device? Based on the components you have listed, am I right in guessing that this is a camera application? We can suggest off-battery LDO's for each of the loads (deserializer, MCU, CAN & LIN). Are you looking to power multiple loads of the same power source? Thanks!

Regards,

Srikanth 

Hi Srikanth,

Thank you for the reply. Please see this decoder board schematic which has DS90UB914, MCU and CAN. We do have other boards with MCU, CAN, LIN and DS90UB928. For the  board with DS90UB914, we also experienced some image stability issue. You can see a video of the issue here. We suspect that power supply may be a factor. We are open to suggestions on how to optimize the power sources. If necessary, please add an engineer familiar with DS90UB914 who can shed light on the issue.

Hi Wei,

            I will look into this and get back to you by next week. Thanks!

Regards,

Srikanth

Hi Srikanth,

Any update on this? Thank you.

Hi Wei,

            Could you provide the details on the following:

(1) Current rating of the power supplies (VDD-1D, VDD-1A, VDD-3D & VDD-3A) of U15 component? The Datasheet for the NVP6021 part does not specify the values.

(2) Voltage and current rating for the power supply pins of the CV2880 device? I could not find the datasheet for this device, it could be sensitive to noise on the power rails.

(3) The part number for the MCU/ADC (component U3)?

I am forwarding this post to our FPD-Link product line to review the DS90UB914 portion of the schematic. My question to the FPD-Link team is regarding the tolerable noise on the 1.8V supply rail. The recommended value is 25mVp-p. Does the corresponding RMS noise (~4mV_RMS) need to be evaluated over the 10Hz to 1MHz frequency range? 

Thanks!

Regards,

Srikanth

Hi Srikanth,

Thank you for the response. Here are the answer to the three questions.

(1) I need to ask for the information. Please allow me several days, for my suppliers are in China and on holiday.

(2) Please refer to this data sheet.

(3) STM32F105RBT6

We had some internal discussion and came up with the following scheme. Please let me know if it works after you get all the information you need. 

TPS65320D-Q1 get power from battery and supply CAN3.3V and VCC5 

TPS7A88-Q1 get power from VCC5 and supply VCC33 and VCC18

TPS7B69-Q1 get power from battery and supply CAN5V

If pin to pin compatible non-automotive grade version available,(for example TPS7B91 replacing TPS7B69-q1) is it possible to use them without any issues?

Hi Wei, 

Thanks for sharing the schematic for the 914, let me review and provide feedback tomorrow. 

Best,

Zoe

Hi Wei, 

From the DS90UB914, the supply noise should be 25mVpp(DC-50Mhz) as measured at the pin of the device. 

The bypass capacitors appear to differ from what we provide in the Typical Applications diagram on the VDDPLL, and VDDCML pins. For the VDDPLL pin, it is recommended to use a 0.01uF, 0.1uF, and 4.7uF capacitor. For the VDDCML pin and  0.01uF, 0.1uF, and 22uF capacitor. The smallest value capacitor should be placed as close to the pin as possible.

A general comment on the 914A schematic here, we typically recommend the PDB signal to be controlled via the SoC instad of an RC control as used here. 

Best,

Zoe

Hi Srikanth,

My Nextchip supplier could not get much more information but provided this data sheet. Would you comment on if the scheme we came up with works for the application? Are TLV752, TLV751, and TLV755 good for ADC power supply?

TPS65320D-Q1 get power from battery and supply CAN3.3V and VCC5 

TPS7A88-Q1 get power from VCC5 and supply VCC33 and VCC18 ((TLV752 replacing TPS7A88-q1 for non-automotive grade lower cost))

TPS7B69-Q1 get power from battery and supply CAN5V  (TPS7B91 replacing TPS7B69-q1 for non-automotive grade lower cost)

Hi Zoe,

Thank you for the input. Can we start a private thread so that you can help review the layout of the PCB?

Hi Wei, 

Sure thing, would you be able to make a new E2E thread for reviewing the 914 layout? This will help the team follow the review. 

Best,

Zoe

Hi Zoe,

I have created the thread here. Thank you.

e2e.ti.com/.../ds90ub914a-q1-output-image-not-stable

Hi Wei,

Great, let's discuss on that thread for the layout review. 

Best,

Zoe

Hi Wei,

           I will look into the datasheet details and get back to you on Monday.

Regards,

Srikanth

Hi Srikanth, do you have any update for me? Thank you.

Hi Wei,

            I apologize for the delay in getting back to you. For the CAN 5V or 3.3V from the 12V battery, TPS7B69-Q1 would be a good choice. I noticed that you have expressed interest in our dual LDO devices such as TPS7A88-Q1, TLV754 & TLV751. While they would save space on the PCB, please take care to ensure that the overall power dissipation (sum of each channel) does not result in exceeding the junction temperature specifications. If thermals do become an issue, TPS7A52 -Q1 would be a good single channel alternative to TPS7A88-Q1 and TPS7A21-Q1 would be a modern single channel alternative to TLV754. For automotive applications, I would recommend our 'Q-1' devices, because they are typically specified to T_J = 150°C and undergo qualifications that meet automotive standards. Please let me know if automotive qualification is not a hard requirement. Thanks!

Regards,

Srikanth

Hi Srikanth,

Thank you for the input. Automotive grade is not hard requirement. Can you recommend lower cost alternatives?

Hi Wei,

            If automotive grade is not a hard requirement, TLV759P is a low cost alternative to TPS7A52-Q1, TPS7A91 is a good low cost & low noise alternative to TLV751 device. TPS7B91 is a low cost alternative to TPS7B69-Q1. Thanks!

Regards,

Srikanth

Hi Srikanth,

Thank you for the suggestions. Does what we came up work, TPS7B91 for CAN5V, TPS65320D-Q1 for CAN3.3V and VCC5V, and TLV752 for VCC3.3V and VCC1.8V? TLV752 is rated for 1A per output, but you mentioned concern over power dissipation. If the current is well within 500mA per rail, will it still be an issue? Are common mode chokes and Schottky diode still recommended between battery power and these IC's?

Hi Wei,

           Regarding TPS65320D-Q1, we can take the recommendation of our Buck team. May I know what is the expected ambient temperature? This would allow us to determine if TLV752 will operate within the recommended junction temperature range. 

Regards,

Srikanth  

It should be-20 to 70 Celsius. Thanks

Hi Wei,

            Please note that our non-automotive grade devices are rated up to T_{J MAX} of 125°C. This would imply that the power dissipation across the LDO (P_D = (V_IN - V_OUT)*I_OUT) would have to be limited to ~0.8W. This could make the use of dual channel LDO's a challenge. I would recommend TPS7B69-Q1/TPS7B91 for the CAN 5V/3.3V supply and TPS7A21-Q1/TPS7A91 to power the ADC. Thanks!

Regards,

Srikanth

Hi Srikanth,

What about TLV1117LV? The noise too high for ADC? Any other issues with it? Thanks.