Hi David.
I hope that you are the right person to answer my questions.
I'm designing a wireless measurement board. Some of the spec:
- Battery powered from one Li-Ion cell.
- Bluetooth module
- 8 bit XMEGA low power microcontroller
- Low noise. ADC is 14 bits, VCC=3V so one LSB =180 µV
- Low power. Idle current is in µA range
- Small size, ~40x50 mm
I have designed some versions already but I have not found out the best way to do it yet.
In one design I have non-isolated DC/DC-converters. This may generate noise but I can not compare because of other problems with the design in this board like a misplaced crystal close to an amplifier and no filters of signals between digital and anlogue. (SPI)
In all other designs I use linear regulators.
I know that if the Bluetooth module have to send with high power (longer range) there will be noise.
The GND planes are separated for digital, Bluetooth and analogue and only connected at the power supplies.
The power supplies is filtered on the input with a LC-filter and on the output with a PI-filter. The L is a multilayer ferrite. C is small for analogue as it is a constant current consumers but large for Bluetooth (~100µF)
During each sample the power can be high, like 100 mA depending of if the board also generate anything at the sampling (like light) or not. After that there will be some calculations or other software tasks and data transmitting to the Bluetooth module that takes ~100 µs but most of the time between the samples the system is idle.
The Bluetooth module have send bursts in the kHz range.
Do you have any idea of what approach that might be best for this kind of power supply? The power must be very noise free but also consume almost nothing during idle.
DC/DC-converter or not is of course the most important question.
There to put and what type of filters is also important.
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