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ADP1613 high noise on output (400mVpp)

Question asked by skibool on Oct 12, 2016
Latest reply on Oct 13, 2016 by skibool

Hello,

 

I designing a power supply +5V and -/+15V with ADP1613 and ADP1614 (+/-15V) for ADAS3022 and DAC LTC2668 from Linear Technology. I use ADP1613 to generate 6.5V from 5V input, then I use LDO to get clean 5V for analog circuit. After doing measurements I've noticed that on the output capacitor of ADP1613 I have 400mVpp noise. I was thinking about layout but I use ADP1614 part for +/-15V an on positive rail output capacitor (+15V) i have noise 10 times lower then on 6.5V rail and layout is almost the same as for 6.5V raill  (ADP1613).

I've attached scope measurements from 6.5V and 15V rail for comparsion.

 

Design for 6.5V rail was generated with Analog tools ADP161x_SEPIC_Cuk_Designer (attached). The negative rail was not used. I was using  ADP161x_SEPIC_Cuk because it allows to design output filter for positive rail. When I compare results from  ADP161x_SEPIC_Cuk_designer and  ADP161x_SEPIC_designer I see that it generates different values for Rc1, Cc1 and Cc2. Wrong Rc1, Cc1 or Cc2 can cause such noise on output ? Does my approach to design (using   ADP161x_SEPIC_Cuk_desiner) is right ? 

 

For my design 5V-CUK_SEPIC_designer.pdf was used.

 

Any suggestion are welcome.

 

Regards Grzegorz 

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