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BQ25570EVM-206: RF Energy Harvesting with BQ25570-EVM

Minh Lam
Intellectual 750 points
Part Number: BQ25570EVM-206
Other Parts Discussed in Thread: BQ25570, MSP430FR5969, BQ25504

Dear TI experts,

I'm doing an RF energy harvesting circuit using BQ25570 for power management, boosting and regulating to supply power to a MCU and different sensors. For BQ25570 to operate, I use 2-stage voltage multiplier (following Karthaus & Fischer's topology) to rectify and initially boost the received AC voltage which is very week (Vpeak = 100mV) to at least 600mVDC. 

Without BQ25570, the voltage boosted can reach 1.2V - 1.8VDC. The input power is around 2mW (3dBm) as measured by a spectrum analyzer.

The problem now is, Vout on the EVM can reach only 1.8V, which is not sufficient for the MCU (MSP430FR5969) and sensors to operate. The minimal voltages for these devices to operate are 1.9V and 2.6V, respectively. So, I'm thinking of connecting VSTOR directly to the supply power of these devices.

Could you please suggest any configuration for the EVM to generate enough voltage to these devices? Thank you very much.

P/S: Please place this thread in a more appropriate forum if it does not fit this forum. Thank you.

  • 0
    TI__Mastermind 21590 points
    Hello Minh,
    I'll suggest switching to the bq25504 if you don't need the buck on the bq25570. You'll want to configure VBAT_OV to about 3V depending on what the maximum voltage for your devices are. What is your current VBAT_OV programmed to?

    Regards,
    Raheem
  • 0 in reply to Raheem
    Intellectual 750 points
    Dear Raheem,

    Thank you for your comment. Now I got only BQ25570 so I've got to use it T_T

    I'm using the bq25570 EVM. VBAT_OV was configured to be 4.17V, approx. VBAT_UV is 1.95V according to the datasheet. VOUT was set to be 1.8V.

    Regarding the buck output, I think I need it. The MCU needs a stable supply voltage for its long life, I think, although I thought I could use VBAT to supply power to the MCU.

    Do you think MSP430fr5969 can work at 1.8V? That's also another question I'd like to ask. I observed sometimes it could operate at <1.8V if just needed to blink a LED, but I need more complicated tasks. My job is to save as much power as possible, so I'd like to put the MCU in sleep mode most of the time, just wake it up for some specific tasks. But I guess, the job with the sensors (I2C, SPI interfaces) would consume a lot of power and timing, so I'm not sure 1.8V can wake it up.
  • 0 in reply to Minh Lam
    TI__Mastermind 21590 points
    Minh,
    If you need a higher voltage for your MCU, you can adjust VOUT_SET to get a higher voltage from the Buck output.
    Regards,
    Raheem
  • 0 in reply to Raheem
    Intellectual 750 points
    Thank you very much Raheem. I'll try this and get back with the result.