Logic chip frequency capabilities

[danielsmusic]

I'm looking to use some of the 4000 series logic chips at around 5MHz (mainly the 4017, AND gates and inverters) for a dot-matrix LED controller. I was wondering if these chips will work efficiently at these speeds? If so, what are their limits?

 

[ericgibbs]

I'm looking to use some of the 4000 series logic chips at around 5MHz (mainly the 4017, AND gates and inverters) for a dot-matrix LED controller. I was wondering if these chips will work efficiently at these speeds? If so, what are their limits?

hi,
Get the data sheet for the HEF4017 from: Datasheet Archive - Free Datasheet Search Engine :: PDF Datasheets :: Data Sheet :: Datasheet :: Application Note : çš„å￾‚æ•° : 规格书 : 技术资料 : ë￾°ì￾´í„°ì‹œíŠ¸ : データ・シート : Fiche technique : Datenblatt : опиÑ￾ание

Look at the bottom of page #4.

 

[Roff]

I'm looking to use some of the 4000 series logic chips at around 5MHz (mainly the 4017, AND gates and inverters) for a dot-matrix LED controller. I was wondering if these chips will work efficiently at these speeds? If so, what are their limits?

The CD4017 is not likely to work well, if at all, at 5MHz. 74HC/HCT4017 works to at least 20MHz.

 

[audioguru]

The max recommended clock for a Texas Instruments CD4017 is 2.5MHz with a 5V supply and 5MHz with a 10V supply.

 

[Roff]

The max recommended clock for a Texas Instruments CD4017 is 2.5MHz with a 5V supply and 5MHz with a 10V supply.

The **broken link removed** says the maximum clock frequency at Vcc=10V is 5MHz typical, 2.5MHz minimum.

 

[danielsmusic]

Looking at the datasheets, it would happily run at 5.5MHz at 15V. I was just wondering if anyone has had any experience running these chips are high frequency. If, so, what to look out for?

 

[audioguru]

At 15V and at 5.5MHz then some of the ordinary Cmos logic chips might be hot.
They can't slew that fast so their Mosfets spend a lot of time in the linear region charging and discharging internal capacitance and getting hot, instead of being saturated where they are designed to be cool.

74HCxxxx high-speed-Cmos switch much quicker and have a lower supply voltage so they would be cool.

My two-cents, I haven't tried it.

 

[danielsmusic]

Yes, I'll go with the 74HC series. Thanks for the advice.

 

[danielsmusic]

Sorry to bump again but I am not worried about the 74HC04. Will not be able to sink enough current for my application.

I need it to sink about 40mA (on the output pins). I'm assuming I will need to use a transistor to do the job, could anyone suggest to me how I could connect it up? I've attached a schematic to show how it's connected at the moment. The second attachment is just my idea.

 

[audioguru]

The max allowed output current from a 74HCxx is 25mA and the max for a package is 50mA. Two inverters can be paralleled to drive 40mA. The LEDs need series current-limiting resistors. A single inverter can drive a PNP emitter-follower transistor and the LEDs still need series current-limiting resistors.

 

[saturn1bguy]

The max allowed output current from a 74HCxx is 25mA and the max for a package is 50mA. Two inverters can be paralleled to drive 40mA.

AG's right here, but parallel more than just two together. Our standard practice was to always use four; it's a bit more wiring but easier on the gates that way. Max current still 50mA...

 

[audioguru]

A single 74HCxx inverter or gate will try to make an output current of 60mA. Two in parallel will drive 40mA into LEDs perfectly.

 

[danielsmusic]

Unfortuantly, because of size and cost requirements I cannot use more than one inverter per set of LEDs. Can anyone suggest to me a good transistor that would switch at around 1MHz? And recommend a good way to wire it?

 

[audioguru]

One 74HC04 costs only $.47US at Digikey today. It has has six inverters inside. The inverter can switch quickly because its output is push-pull. A single transistor turns off slowly but a complimentary push pull pair can switch quickly.

 

[Ubergeek63]

Digi-Key - 296-4024-5-ND (Texas Instruments - SN74ABT540N)

Can go quite fast and pull 128mA to gnd on EVERY pin