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.
Thanks,
Khoi Ly
