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AD5755 DCDC doesn`t start up

Question asked by PingvinFelix on Dec 6, 2014
Latest reply on Dec 9, 2014 by msamera

Hi everyone! I has a project with AD5755 chip. I started to start it up and got a problem. A problem wich DCDC channels of the chip. Please look at attached file. At first  time I don`t place components L7 and L11 (ferrite beard) to the PCB and scope SW pin after elabled DCDC in channel control register. I see that the internal swich starts up with right frequency (I tried 250 and 410 in DCDC control register) and it seems that there no problems. But when I get back L11 to PCB I immediately get a 5V at SW pin without any switch activity on the scope (and also without L11 on Vboost  pin there is no voltage. The presence of storage inductance (L7) doens`t matters.

Can anybody have anydcdc_1.JPGideas about this situation?