i am using AD9912 as a LO source for battery operated equipment. for that one i am desining power supply section( input volatge from battery is 14.8Volt )
1) 14.8 V to 5V through Switching regulator (part No RECOM regulator) then LDO AD3338 for 3.3 Volt
2) 14.8V to 2.2 V through Switching regulator(part no yet not finalized, LMZ1002 from TI) then LDO ADP172 for 1.8 Volt (300mA Load)
how much PSRR and ripple will be achieved with ADP172 (because drop out volatge is less than 1 Volt)
or we can decrase the input to ADP172 to increase the efficiency insipte PSRR & Ripple will not reduced .
two switching regulator in one board will not create any problem ( because board contain RF circuits.) or i have go to any other approch.
In general I would point you to the ADIsimPower tool for identifying your best options
Here are a few options for you in the meantime:
- For the 14.8V to 5V you can use the ADP2370 or the ADP2300…
- For the 14.8V to 5V you can use the ADP2370 or the ADP2300 (1/2/3)
- For the LDO from 5V to 3.3V we have many options, ADP151 is the lowest noise part we have, alternatively you can use the ADP125 or ADP1707
- For 14.8 to 2.2V again the ADP2370 or ADP2300 family is a good option.
- For 2.2V to 1.8V the ADP151 may have better PSRR than the ADP172
The linear regulator design tools attempts to predict the PSRR at full load based on some characterization and data on the datasheet. If you download and run you case scenario you can compare the PSRR listed by the design tool. You just need to manually select the LDO you want to design with.
ADI Linear Regulator Design Tool and Parametric Search
If the layout is done appropriately having 2 switching regulators on the board will not be an issue, shielded inductors and adequate input bypass capacitance will be necessary. Another option is to use dual switching regulators (like the ADP2323) that share a single internal clock or have the ability to synchronize to a system clock.