1. Home
  2. Electronics Design
  3. Maximum current for analog switch

Maximum current for analog switch

Say I use an analog switch like this one to drive a capacitance or rather the gate of a FET to turn it on with 5V and turn it off shunting to 0V

formatting link

It's a 20 ohms part if driven from 5V

The gate has total charge of a couple of nC. Peak current will be 250mA for some tens of ns.

Would this part survive?

Compare it to a 2N7002 FET, isn't the FET silicon area about the same inside the 4053 IC to yield the same Rdson, so it should have the same robustness and same peak currents etc?

Regards

Klaus

Reply to
klaus.kragelund
Loading thread data ...

PowerMOS Fet's have a different channel construction than integrated switches, and much higher voltage sustaining, so there are significant area differences, but you _should_ be OK...

Watch out for ground bounce screwing up the drive.

A high rep rate may toast the wirebonds or the chip metalization... I'd run some equivalent tests before committing to production.

I note that the datasheet no longer shows on resistance as a function of signal voltage... near the rails on resistance will be higher.

The LVX4053 is one of the LVX family that I re-did for ON-Semi so that it could be processed at the Chartered foundry...

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

Den tirsdag den 16. august 2016 kl. 00.04.07 UTC+2 skrev snipped-for-privacy@gmail.com:

if it is just 5V on off why not a regular gate?

-Lasse

Reply to
Lasse Langwadt Christensen

That is the big question. Klaus, how often does it switch per second? Machine-gun style or regular intervals?

For ground bounce, yes, but beyond that I'd contact ON Semi about some more data. SOA, temp diagrams, the stuff that comes with discrete FETs.

Datasheets became dumbed down a lot since the 70's, just like operating systems did :-(

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Maybe not 250 mA. At higher voltage drops, the fets inside the mux will quit being ohmic and go more constant-current.

Sure. The higher the switch frequency, the more the power dissipation.

It's probably a smaller chunk of silcon, and it drives both edges, but it should be OK. First-order, the power dissipation in the driver is independent of Rds-on. P = Cload * Vcc * F.

As asked elsewhere, why not use a gate?

These mux's do have a break-before-make time delay, which might save a bit of shoot-through dissipation.

I wanted to use a similar mux a while back, as a gate driver, but the make-before-break delay was a problem. I have some measurements, somewhere.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

I see the discussion is about IC switches, even though it hasn't addressed the 1-ohm and sub-1-ohm parts that are available. (We have a nice table of 4053' style CMOS spdt switches in AoE III, Table 13.7, page 917, and CMOS switches in general, Table 3.3, page 176.)

But this type of discussion ignores the possibility of roll-your-own high-current analog switches, using your selected power MOSFETs. They can handle currents from mA to hundreds of amps. The best have Ron = 0.003 ohms. See Figure 3.107, page 205, for the basic configuration, and Table 3.5 for a selection of candidate MOSFETs.

--
 Thanks, 
    - Win
Reply to
Winfield Hill

In this case a low Ron may lead to disastrous current levels. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

There are lots of nice cheap mosfet gate driver chips.

Shortly you design some really cool circuit, some IC jock integrates it.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics
Reply to
John Larkin

As I crash for the night I realize an error... the peak current isn't VDD/RON, it's IDSS... it's now the OP's responsibility to check his numbers >:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

I might be using this one:

formatting link

It has a spec for maximum current of 50mA, and that is at least something to design after (will contact NXP for more information on max peak current)

Cheers

Klaus

Reply to
Klaus Kragelund

Good question :-)

A 74LVC1GU04 inverter is cheap also, has 0.5V "drop" at 32mA, which translates to 15 ohm. The analog switch 74LVC1G3157 has 1.5 ohms. So it's ten fold better at the same price

Also, the analog switch comes in different Ron values, so if I want more drive, it easy to change to a different part.

Cheers

Klaus

Reply to
Klaus Kragelund

18kHz. And the gate charge is below 10nC, so a total power dissipation in the gate of 0.5mW from gate charge, which includes miller. The peak currents is higher though

Good idea.

Sometimes for nostalgic, I dig up to the RCA 4000 series datasheets. Lots of graphs and good stuff

Cheers

Klaus

Reply to
Klaus Kragelund

r the gate of a FET to turn it on with 5V and turn it off shunting to 0V

for some tens of ns.

side the 4053 IC to yield the same Rdson, so it should have the same robust ness and same peak currents etc?

Thats actually why I looked at it. Since feeding a P and N FET will cause s ome cross conduction. With the analog switch I have break before make, and I save a diode also. Normally the turn off is made faster with a diode acro ss the gate resistor, in my case I can place the resistor in the VCC path t o the mux

Cheers

Klaus

Reply to
Klaus Kragelund

I am actually rolling my own right now, but it's just a FET buffer. But I want super low price, and the mux removes 2 FETs and 1 diode times 6 in my circuit, so 18 components :-)

Cheers

Klaus

Reply to
Klaus Kragelund

How do I check the IDSS of an internal FET inside the mux?

Do I just make a test with a big cap and check the peak current?

Cheers

Klaus

Reply to
Klaus Kragelund

Sounds like it would survive worse than that, especially since it's unlikely to stay ohmic when dropping 5V.

Try it with a capacitor 100 times that large--I bet it survives fine.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

FYI, there may be spooky behavior. The HC version carries a peculiar warning,

formatting link
Note [1], page 5.

Why they screwed up the switch design on this one, I have no idea...

Doesn't look like the LVXT has the same warnings, so who knows.

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

formatting link

Reply to
Tim Williams

Well spotted. Sure sounds like something funny going on

Thanks

Klaus

Reply to
Klaus Kragelund

How do you interpret what is going on there?

--sp

--
Best regards,  
Spehro Pefhany 
Amazon link for AoE 3rd Edition:            http://tinyurl.com/ntrpwu8
Reply to
Spehro Pefhany

On the switch section, tie IN to VDD, OUT to VEE thru a small sense resistor. Turn it on for a short period while observing sense resistor with a 'scope. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.