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LP87702-Q1: LP87702 chip evaluation

user6310590
Prodigy 180 points
Part Number: LP87702-Q1
Other Parts Discussed in Thread: LP87702,

Your company’s LP87702 chip, I read the specification, dual buck+boost, which is more suitable for our company’s mcu+can power supply application scenario.
Our company is input 3.8V~5V, fixed output 3.3V and 1.25V, boost is 3.3V input and 5V output, and the two bucks are required to output 3.3V and 1.25V normally. Now there are the following questions that need your help to confirm
1: I read the specification mentioned that the maximum support current is 3.5A. Does this refer to the total current of 2 bucks or the current of a single buck
2: It is seen in the specification that the EN pin and iic are multiplexed. If it is applied to iic, what is your company's corresponding car gauge model?
3: The reference voltage is not found in the specification, so I don’t know how to set the feedback resistance
4: I see that the dynamic characteristics of buck at 4MHz in the specifications are not very strong. Is there any room for optimization? We hope to reduce it to less than 50mV.
5: This chip of your company has a spread spectrum function. Is spread spectrum enabled by default? What is the spread spectrum range?
6: How much does your company's spread spectrum function optimize EMC? Are there relevant test data and reports?

  • 0
    TI__Expert 4355 points

    Hi,

    1. 3.5 A is maximum current drawn from a single buck but it may vary depending on the model, for example, LP87702DRHBRQ1 buck1 max DC current is 3 A and buck2 max DC current is 3.5 A. Refer to the technical reference manuals for more details.

    2. Could you clarify the question a bit?

    3. The default output voltage is defined in the OTP and it can be changed via I2C by writing to the BUCK0_VSET and BUCK1_VSET registers. See the technical reference manuals for the default output voltages. No voltage divider required in the feedback.

    4. Optimizing layout and adding additional point of load capacitors can help with the transient performance.

    5. Default spread spectrum state is defined in the OTP and the spread spectrum can be enabled or disabled via I2C. For LP87702DRHBRQ1, LP87702KRHBRQ1 and LP877020RHBRQ1 spread spectrum is disabled by default. Spread spectrum varies the switching frequency between 0.85 x fsw - fsw where fsw is the switching frequency.

    6. We don't have public measurement data about the spread spectrum performance as the effect on EMI depends on many different aspects of the system. Layout, external components, etc. all affect the EMI.

    Best regards,

    Samuli Piispanen

  • 0 in reply to Samuli Piispanen
    Prodigy 180 points

    The power-on of our entire system is controlled by the MCU. Now what is needed is the power supply for the MCU. Therefore, the LP87702-Q1 is required to output 3.3V and 1.25V fixedly. It cannot be adjusted by IIC because IIC comes from the MCU. Is there a solution?

  • 0 in reply to user6310590
    TI__Expert 4355 points

    Hi,

    In that case, this would require a custom OTP which is configured to match your desired configuration. However, that requires an approved business case. For that, contact your local sales representative. You can find customer support at https://ticsc.service-now.com/csm/

    Best regards,

    Samuli Piispanen

  • 0 in reply to Samuli Piispanen
    Prodigy 180 points

    7：There is no related design of this chip on webench，Can't do simulation

    8：Is there a downloader for configuration? Is there a corresponding host computer tool?

  • 0 in reply to user6310590
    TI__Expert 4355 points

    Hi,

    7. LP87702-Q1 has SIMPLIS transient and SPICE Average models available. These are available at the LP87702-Q1 product page for a download.

    8. OTP configurations are loaded to devices at the factory. It is not possible to modify the OTP configuration afterwards.

    Best regards,

    Samuli Piispanen

  • 0 in reply to Samuli Piispanen
    Prodigy 180 points

    Can I use SIMPLIS go to simulate when add your LP87702 model?

  • 0 in reply to user6310590
    TI__Expert 4355 points

    Hi,

    You can use the SIMPLIS transient model to simulate the transient performance of the buck regulators. The boost model isn't included in the LP87702-Q1 SIMPLIS model. Simulations require a version of the software that supports encrypted models. The free version of the simulator "SIMPLIS Elements" does not support encrypted models and therefore it won't work.

    Best regards,

    Samuli Piispanen