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Large Ripple at the ADP1614 Output

The above image shows the schematics of the two-stage boost conversion. 

Stage 1: Battery/Bench-top power supply to ADP1614 to obtain regulated 5V output. The 5V is then used for the following:

           a. It connects to an ADP7104 (P3 on the schematic) which power a microcontroller at 3.3V

           b. It directly powers a DDS AD9833 and its 10Mhz oscillator

           c. It directly powers a voltage reference that outputs 2.5V

           d. It is stepped up by LTM8049 +/-12V converter

Stage 2: The LTM8049 converter powers 2 LT1037 op amps, one as a non-inverting op amp and the other as attenuating inverting op amp) and an LT6011 dual channels as second order low pass filter. 

The following describes the behaviors of the system:

1. the ADP1614 outputs very large ripples even though the average output matches with the formula 1.245x(1+ 3000/1000). The ripples tend to increase as the input voltage decreases. At 4V input voltage, the ripple pk-pk is almost 1V.

2. The LTM8049 is well regulated and performs as expected

3.  The output of DDS AD9833 is dependent on the voltage supply (5V) from the AD1614. It's sine-wave amplitude changes as the voltage input to the AD1614 changes. 

Question: Is there something wrong with how I select the parts for the AD1614? Do you know a solution for this problem? Ideally, I would like the AD1614 to have very good regulation so that the DDS AD9833 output is very stable.


Khoi Ly

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