BQ25505: Ultra-low power operation

We designed an energy harvesting device that will generate 0.6V at 100nA (similar to another question on the forum). We could stack several devices to get >2V but are not sure if we can support the BQ25505's total power input requirements. Have several questions about the quiescent current, Vin and Pin.

1. Quiescent current: Average is 325-400nA when Vin is 0V, and Vstor is 2.1V. 

1. Over what time period is the 325nA average taken? 

2. Is this current approximately continuous or is there a duty cycle? If duty cycle, is it fixed or programmable?

3. Does the BQ circuitry draw that current from any source tied to Vstor (such as a supercap on VBAT_SEC meant to service the load)?

4. If VSTOR < VSTOR_CHGEN, and Vin is 0 or <100mV, how does this affect quiescent current? Is the circuitry effectively ‘off’ at this point until Vin>Vin(CS)?

5. If the circuitry draws current from VSTOR, and the circuit is effectively off when VSTOR<VSTOR_CHGEN (questions 1c and 1d), can we prevent the circuitry from being powered by VBAT_SEC when VSTOR>VSTOR_CHGEN and Vin=0?

• Quiescent Current Range: 

  1. With the duty cycle time in ms, my assumption is that the quiescent current draw is effectively 325nA, but what is the actual range of the quiescent current (0-1uA for example)? We could handle 1uA, for example, with a very low duty cycle (e.g., 1% or less).

  2. What is the duration of the current draw at the high end of that range (for example, 0.2ms at 1uA)?

• Datasheet changes

  1. The datasheet for the BQ25505 for the evaluation board we bought has been revised since then (version dated September 2013).  The most recent revision (Rev F dated March 2019) has some important differences.
  2. Vin for cold start changed from 330mV(MIN) to 600mV(TYP)/700mV(MAX). Does this reflect a correction to the specifications or is it a design change? If we order more chips, will they have a 700mV worse case for cold start/normal charging?
  3. Same question for minimum power input for cold start and normal charging. Old Pin was 5uW, but the most recent version says it’s 15uW.

• Voltage and Power Requirements: To make sure I fully understand the Vin and Pin requirements - 

1. 1. The Rev F datasheet states Vin of 600mV (TYP). However, my BQ25505 evaluation board successfully enters the cold start and booster charging state with just 340mV. So, again, does the datasheet change reflect a correction to the cold start Vin voltage spec or is this a chip design change (i.e., higher cold start V) that must be considered if we use current production BQ25505 chips?
   2. Is the Pin minimum of 15uW (per new DS) a hard number? For example, 15uW would require Iin of 45uA @ 330mV.
      1. If we managed to design with an input of >0.6V but with current less than 300nA, could we still meet the Pin requirements using the formula in the datasheet?
      2. If 15uW is a hard minimum for Pin, then that is effectively an Iin minimum of 8uA (or 25uA new) @ 0.6V.

Thanks for your help in understanding how the BQ chip works and if we can utilize it in our design.