Switch Mode Pump (SMP) effects on Band pass Filter Out put

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DeAa_335316
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 whenever i connect 10uH inductor to power supply ... it will effect my filter output. it create the noise . its boost up the power but effecting filter result .. how to resolve this ..

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ETRO_SSN583
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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.

   

 

   

    

   

          

   

https://www.dropbox.com/s/ruaf9booe17jk8n/PCB%20Layout.zip?dl=0

   

https://www.dropbox.com/s/2h96beh1fbvz4e2/noise_notes.zip?dl=0

   

   

 

   

Grounds critical.

   

 

   

Regards, Dana.

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DeAa_335316
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 I/p voltage = 3.3v (Voltage Source MiniProg3) 

   

M8C running at = 3.3v

   

******i want to generating 4.7v- 5v for other device 

   

L=10uH

   

schottky =1N5818

   

C=100uF (becoz 10uF not able to boost up 5v ...)

   

SwitchMode =ON

   

Trip Voltage Lavel=4.81V(5V)

   

LVD = Disable

   

# Plz Find the the attached Archive... 

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ETRO_SSN583
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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

   

PGA_2 ?

   

 

   

Regards, Dana.

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DeAa_335316
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plz find the attached file ..

   

tell me if i use this circuit it will effect my BPF 20khz frequency or not .

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ETRO_SSN583
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 As sated before, ANY switch mode power supply generates noise,

   

ground bounce, and takes a great deal of effort in layout, capacitor

   

selection, etc..

   

 

   

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

   

cheap.

   

 

   

Regards, Dana.

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DeAa_335316
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 So what is the use of SMP if it is effecting microcontroller  process , filter ,PWM  , generating noise and  drive only 50 mA.

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Bob_Marlowe
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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.

   

 

   

Bob

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ETRO_SSN583
Level 9
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 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

   

 

   

Regards, Dana.

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