Looking for small SPST SMD "switch" (cmos?)

luvdunhill · 20th March 2010, 05:23 PM

I'm looking for a small switch to use to change the gain of an amplifier. The way the amp is drawn, a single SPST will work, the smaller footprint the better. I would just switch in a second resistor that would then be in parallel with the first resistor. I have a 5v supply to work with as an aux supply, but also have access to +-12V, but would prefer not to use this. I'd like to have the option of using a mechanical switch to trigger four of these, or using a microcontroller. I've never used a CMOS switch, but I'm guessing this is exactly what I want.. but feel free to correct me

soekris · 22nd March 2010, 01:05 AM

You haven't stated all your parameters, but for audio I like, available at DigiKey:

TC4S66F in sot23-5
DG448 in sot23-6, lower rds-on

Or try their search engines....

Soren

luvdunhill · 22nd March 2010, 04:55 PM

Soren:

I'd like to be able to use a 5v control voltage. Also, I need to handle rail to rail analog voltages, maximum is probably +-15V. Also, as many throws as possible, but when I look at for example some of the sp4t, they have low voltage limitations. Rds-on isn't a huge deal, as it will be in series with a large resistor anyways to set the gain of the amplifier.

Since it's being used in a feedback loop, perhaps even the +-15V can be relaxed, but I'm just not sure. If so, then here is a sp4t that looks nice:

http://focus.ti.com/lit/ds/symlink/ts3a5017.pdf

... now if I could find a 5v version and to avoid a regulator for this chip..

mutter · 22nd March 2010, 05:19 PM

What about this?

ADG1409 | 4 ? Ron, 4 - /8 - Channel ±15 V/+12 V/±5 V iCMOS Multiplexer | Multiplexers (Muxes) | Switches/Multiplexers | Analog Devices

Haven't used it but was looking at it for a project.

Neil Davis · 22nd March 2010, 05:22 PM

Quote:

Originally Posted by luvdunhill

Soren:

I'd like to be able to use a 5v control voltage. Also, I need to handle rail to rail analog voltages, maximum is probably +-15V. Also, as many throws as possible, but when I look at for example some of the sp4t, they have low voltage limitations. Rds-on isn't a huge deal, as it will be in series with a large resistor anyways to set the gain of the amplifier.

The Rds-on is actually fairly important, because the switch resistance is usually dependent on the input voltage. A switch with low RDS-on will have lower distortion, because the voltage-dependent resistance introduces distortion.

Quote:

... now if I could find a 5v version and to avoid a regulator for this chip..

The ADG736 and others in that series have very low resistance and work at 5v.

Another solution is to use a digital potentiometer. Maxim and Xicor have many to choose from. If you can generate the I2C control signals, the MAX5477 is a good choice. Of course, you could also use a digital volume control such as the PGA4311.

luvdunhill · 22nd March 2010, 08:11 PM

all good suggestions. Thanks everyone. I'll pour over some more choices and report back later!

20th March 2010, 05:23 PM	#1
luvdunhill diyAudio Member Join Date: Jul 2006	Looking for small SPST SMD "switch" (cmos?) I'm looking for a small switch to use to change the gain of an amplifier. The way the amp is drawn, a single SPST will work, the smaller footprint the better. I would just switch in a second resistor that would then be in parallel with the first resistor. I have a 5v supply to work with as an aux supply, but also have access to +-12V, but would prefer not to use this. I'd like to have the option of using a mechanical switch to trigger four of these, or using a microcontroller. I've never used a CMOS switch, but I'm guessing this is exactly what I want.. but feel free to correct me

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22nd March 2010, 01:05 AM	#2
soekris diyAudio Member Join Date: Jun 2009	You haven't stated all your parameters, but for audio I like, available at DigiKey: TC4S66F in sot23-5 DG448 in sot23-6, lower rds-on Or try their search engines.... Soren

22nd March 2010, 04:55 PM	#3
luvdunhill diyAudio Member Join Date: Jul 2006	Soren: I'd like to be able to use a 5v control voltage. Also, I need to handle rail to rail analog voltages, maximum is probably +-15V. Also, as many throws as possible, but when I look at for example some of the sp4t, they have low voltage limitations. Rds-on isn't a huge deal, as it will be in series with a large resistor anyways to set the gain of the amplifier. Since it's being used in a feedback loop, perhaps even the +-15V can be relaxed, but I'm just not sure. If so, then here is a sp4t that looks nice: http://focus.ti.com/lit/ds/symlink/ts3a5017.pdf ... now if I could find a 5v version and to avoid a regulator for this chip..

22nd March 2010, 05:19 PM	#4
mutter diyAudio Member Join Date: Mar 2009	What about this? ADG1409 \| 4 ? Ron, 4 - /8 - Channel ±15 V/+12 V/±5 V iCMOS Multiplexer \| Multiplexers (Muxes) \| Switches/Multiplexers \| Analog Devices Haven't used it but was looking at it for a project.

22nd March 2010, 08:11 PM	#6
luvdunhill diyAudio Member Join Date: Jul 2006	all good suggestions. Thanks everyone. I'll pour over some more choices and report back later!