Author Topic: Voltage Divider for RF Switch control  (Read 896 times)

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Offline Nikos A.Topic starter

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Voltage Divider for RF Switch control
« on: May 14, 2019, 02:28:58 pm »
Hi everyone,

I am going to use a RF SP4T switch for a project and the control input voltage for the high state is 2.5 - 3.3V.
I will send the signals through an Arduino which will be fed with 5V and thus the digital pin output will be 5V.
Can I use a voltage divider to step down the signal to 3V for this purpose?

Thanks in advance
 

Offline pwlps

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Re: Voltage Divider for RF Switch control
« Reply #1 on: May 15, 2019, 04:30:00 pm »
Yes but you might need to take into account the current drawn by the switch  to dimension your voltage divider. Check the high and low-state currents of the control inputs of your SP4T.  If you can afford having a divider  drawing much more current (say a factor of 5-10), then  loading the divider by the control input will have negligible effect, otherwise recalculate the divider. For example if the current is 1mA at 3V it is equivalent to have a 3.3k resistance in parallel  with the low-side resistance of the divider.

Edit: you will find the formula for a loaded divider here: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html
« Last Edit: May 15, 2019, 04:43:32 pm by pwlps »
 

Offline Nikos A.Topic starter

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Re: Voltage Divider for RF Switch control
« Reply #2 on: May 16, 2019, 08:07:30 am »
The datasheet does not provide such an information for control current.. Maybe this is negligible?
 

Offline pwlps

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Re: Voltage Divider for RF Switch control
« Reply #3 on: May 16, 2019, 09:10:44 am »
The datasheet does not provide such an information for control current.. Maybe this is negligible?

They say
Quote
Switching is controlled by two CMOS/TTL compatible control voltage inputs: VC1 and VC2.

This is of course misleading because the max input voltage is 3.3V which is LVTTL and not TTL, at any rate if these are CMOS inputs then the current is negligible indeed.
NB. some useful refs. on CMOS/TTL specs:
https://forum.allaboutcircuits.com/threads/cmos-and-lvttl-voltage-levels.62014/
https://www.classe.cornell.edu/~ib38/teaching/p360/lectures/wk09/l26/EE2301Exp3F10.pdf
« Last Edit: May 16, 2019, 09:12:33 am by pwlps »
 

Offline Nikos A.Topic starter

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Re: Voltage Divider for RF Switch control
« Reply #4 on: May 17, 2019, 04:39:34 am »
Thank you very much for your help!!
 


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