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BQ25504. Which are the instrumentation setups for obtaining the datasheet pictures from Fig. 1 to Fig. 7 ?

Other Parts Discussed in Thread: BQ25504

BQ25504. The datasheet shows several pictures of efficiency versus input voltage sweep or current sweep. I'm trying to reproduce some of them in my lab using a SMU from Keysight and other instruments. But I don’t understand the parameters and the instruments setup quite well … For instance:

-          How are you connecting the source and measurement unit (SMU) at the input (through a series resistor while in voltage mode?).

-          Which is Icomp? Is it perhaps the source meter in voltage mode and the Icomp the compliance current limit?

-          Where is connected the output system load?, At the battery Vbat ? perhaps replaced by a simulated battery using another SMU? Is the Vstor left unconnected while performing such measurements?

-          Could you draw a pair of schematics of the instrumentation system for obtaining for instance Fig. 1 (voltage sweep while fixing the input current at 10 uA) and Fig. 4 (current sweep while fixing the voltage at 2 V)?

Thank you very much for your attention,

  • For figure 1:

    1. Set the VBAT_OV threshold to 5.5V.

    2. Connect source meter to VSTOR. Set the source meter to measure current and voltage source (VSRC) o 1.8V, 3.0V, and 5.5V.

    3. Connect source meter to VIN_DC. Set current compliance to 10 uA and step voltage source (VSRC) from 0 to 3V in a step of 0.2V.

      

  • Yes, Ok, but my problem is precisely with your proposed step #3. This chip is aimed to regulate the input voltage to the MPP value. It takes every 16 s a sample of the open circuit voltage Vin_DC for 250 ms and then for the remaining time between samples it tries to adjust the Vin_DC to the fractional value derived through the resistors from the sampled open circuit voltage already stored in the reference capacitor. Thus, imposing directly the Vin_DC by means of a voltage source instrument, I think that it is not correct, because you are not letting the system work in its own, trying to follow the MPP voltage. Perhaps, shouldn't you add a series resistor with the voltage power supply, like the 20 Ohm they recommend to use with the demonstration kit, or even better, why not to use a current source instead, adjusting in this case the voltage compliance (limit voltage) ?

    Best regards,
  • You are correct on the how the part works. However, the actural VIN_DC you are measuring IN STEP 3 is the MPP value. Vsrc on the source meter can be considered as the open circuit voltage. When the part is in the main boost mode, the input voltage will be clamped down to the programmed MPP threshold when the input power is sufficient. The measured input voltage will be this clamped voltage not the open circuit voltage in the main boost mode. When VSTOR reaches the VBAT_OV, input voltage will return to the open circuit voltage.