I am searching for a Li-polymer 1A charger with a 3V regulated output. I have found Linear LTC355x serie but can't, after reading many "LDO vs Switching" debates, understand the use of both on the same chip. LTC3553, for example, offers a 200mA buck and 150mA LDO.
I need to drop the USB 5V and battery 3.3-4.2V to 3.0V with a 170mA maximum draw. Space on the PCB is a premium so I'd prefer a combined chip. The PCB also contains 868mhz and 1575mhz antennas so a linear converter might be better ?
Should I choose between LDO or buck (I couldn't find a only-LDO or only-Buck chip) and disable the other ? Should the buck be the main source and the LDO the backup/standby source ? Is it only used to output different tensions, for example, 1.2V and 3.0V ?
EDIT : Thank you for your answers. They got me thinking about the VINLDO pin and I was wondering if feeding the LDO from the Buck to obtain a clean output is worth a try ? Assuming :
- Battery safe tension range is 3.0-4.2V and VUSB is 5.0V.
- All devices on the PCB could use 2.8V.
- Buck is needed to obtain an efficient conversion from > 4.0V.
- LDO is needed to obtain a clean output.
- => The buck could output 3.0V to the LDO which in turn would produce a clean 2.8V ?