LTC4015: No infet, almost no buck converter

Some difficulties in geting my LTC4015-Board running the first time. Technical data:

- V-in = 12V ... 20V

- V-sys = 8V ... 20V

- V-bat = 8V ... 12,8V,  8 x NiMH in series

- I chose 3xLiIon programmable

- I-charge = 3A (max)

- I-discharge = 3A (max)

- I-sys: 4A max

- No software installed yet.

The whole system went perfectly on demo circuit DC2039A.

The two difficulties are:

- 1. Infet-Pin (34) was never above V-in, so the Fet of the ideal diode was never conducting. Only the body diode of the in-Fet. It got warm to 90°C.

- 2. Buck Converter was never running, excepted one situation: Instead of a battery I took 6 x SuperCaps in series (100F, 2,7V each + 8 x 3,2 kOhm to symmetrize) to make the charge- and discharge time smaller. When the SuperCap voltage was between 5,0V and 5,2V the buck converter startet , when V-in startet, but stopped 1 sec later. The SuperCap was charged with some mV.

Now my questions:

- Why do Infet-Pin and Buck-Converter not start ? Are there any pre-conditions I did not take care off ?

I checked the boost capacitor (datasheet p.44, 470nF like the democircuit) between boost and SW-pin. My Buck-Mosfets are PSMN9R1-30YL,115 with input capacitance = 894pF. It should work in my eyes ...

Thanks for support

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