If you use a switching power solution inherently that generates more noise.
But layout, choice of cap technology (bulk, polymer tantalum vs regular tants
vs simple electrolytics, polymer the best) all count. Good cermamic disks
(check datasheets for performance) also matter.
Use your DSO, set it to infinite persistence, and hunt down pk-pk noise problems.
an20973.pdf 210.5 K
Do you have a spectrum analyzer ? What noise do you see coming
thru BP Filter. I noticed your BP is running at 20 Khz, not suprised you
are seeing effects of SMP.
You also have G = 10 thru filter. Also I do not see where you have any G set for
As sated before, ANY switch mode power supply generates noise,
ground bounce, and takes a great deal of effort in layout, capacitor
You could consider using a split power system, an LDO linear reg for PSOC
and SMP for the rest of the high current system loads. The linear reg offers
noise rejection (consult datasheet for f vs noise rejection perfromance).
You could try using an additional L and C to filter Vdd of PSOC. Using a
scope, especially a DSO with FFT, can help finding the problem areas.
There are low noise SMP parts, TI, NSC, Micrel, you could look at in lieu
of using the PSOC approach. That also have LDO's in them. And generally
So what is the use of SMP if it is effecting microcontroller process , filter ,PWM , generating noise and drive only 50 mA.
I was searching yesterday for a hint Cypress gave concerning SMP but couldn't find it. They suggested to stop SMP during an ADC conversion due to the noise an SMP produces. After conversion done (within some µs) SMP is switched on again.
And: The use of an SMP is not to drive some LEDs, but to power a PSoC with a low voltage source.
Would you use in any design an SMP if -
1) Doing 20 bit A/D conversions NO (or at minimum split isolated supplies, I would do that even at 12 bits)
2) Driving a few LED and nothing else YES
3) Filtering signals expecting 40+ db response EVALUATE
4) Driving motors and a LCD display YES
5) Using PLLs and expecting low jitter NO