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LTC4125 strange behaviour

Question asked by crayone on Jun 4, 2018
Latest reply on Jun 19, 2018 by WATaylor

I'm using the LTC4125 power transmitter for a wireless charger in conjuction with LTC4120 device.
In attachment you can see the schematic of TX unit.
I notice a strange behaviour.
With no RX device coupled, When I apply the power source (5V), the LTC4125 absorbs the maximum current determined by R1,R2 and R6 (1.8A).
I have set R6 to 470K to reduce current to 380mA for further testings.
In picture 1 and 2 you can see voltage on both sides of inductor L1.
Frequency is about 106 KHz.
Every 4 seconds voltage changes as in picture 3 and 4, for a very short time and current drops to a few mAs.
I think the behavior should be exactly the opposite: normally the LTC4125 should absorbs a few mAs. Current should raise when he has been coupled with the RX inductor.
L1 is a 8uH inductor (760308102207 from Wurth).
I've tried different types of inductor for L1 (760308100110, 760308101103, 760308101105) with no success.
Some one can help me debugging this circuit?

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