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BQ24753A / jumps between regulation currents

Other Parts Discussed in Thread: BQ24753A, BQ24753

Dear e2e,

In a setup with a 15V power net DC supply and a 12.6V Accu pack, we use the BQ24753A with a ACSET Limit 2A (via resistor divider) and configured also the SRSET Limit via a resistor divider to 2A.
There we measured a maximum current limited through the dynamic power management of approximately 1.8A.

In case of almost no system load current, we observe approximately 1A as load current with low accu charge level.

I guess 2A (1.8A) are not possible because of the small difference between the max. accu voltage and the DC net power.
And also because of the fix of 300kHz and Duty Cycles of the DC/DC for the charge current. Is this a valid assumption ?

Our load is a CPU module running Windows. If we power the CPU module, it consumes about 0.9A system load current with Windows in Idle state.
We observe strange behavious as sometimes we get the maximum of approximately 1.8A (0.9A for loading the accu) from the net power supply
while sometimes we get only approximately 1.2A (0.3A for loading the accu). It appears that it jumps between these two regulation currents
from the 15V DC net power supply.

We measured the signals to the Gate of the High Side and Low Side MOSFET´s in the charge path as well as the switching node.
There we saw, that we have in the case of limitation a shorter High Side MOSFET Duty Cycle which starts a little bit later.

Questions:
- Is above behavior normal operation respective, what are the reasons for this behavior?
- What can be improved to always get the maximum current available for loading the accu?
- Do you see a problem, if the BQ24753 switches regularly between the above mentioned current levels, although the load current should be nearly stable?

If needed I can provide schematics and scope plots for full and reduced load offline. 

Kind regards,
Uli