Driving several chips with a single oscillator

[[email protected]]

I am making a new PCB where size and weight are critical. I would
like to drive two chips (a microcontroller and a Bluetooth chip) using
a single crystal oscillator. What is the effect of driving several
chips with a single oscillator? Is it possible?

Oscillator: Abracon AP2S oscillator - http://www.abracon.com/Oscillators/AP2S.pdf
microcontroller: Microchip dsPIC30F4013 -
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010345
Bluetooth chip: National LMX9830 - https://www.national.com/pf/LM/LMX9830.html

Thanks

 

[Tam/WB2TT]

I am making a new PCB where size and weight are critical. I would
like to drive two chips (a microcontroller and a Bluetooth chip) using
a single crystal oscillator. What is the effect of driving several
chips with a single oscillator? Is it possible?

Oscillator: Abracon AP2S oscillator -
http://www.abracon.com/Oscillators/AP2S.pdf
microcontroller: Microchip dsPIC30F4013 -
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010345
Bluetooth chip: National LMX9830 -
https://www.national.com/pf/LM/LMX9830.html

Thanks

So long as it is the same frequency, or multiple thereof, why would you
think it is not possible? Am I missing something?

Tam

 

[[email protected]]

So long as it is the same frequency, or multiple thereof, why would you
think it is not possible? Am I missing something?

Tam

I'm wondering if the input capacitance of the chips affects the
oscillator. The oscillator has an optimal load capacitance that it
performs with. I can't seem to find the input capacitance information
in the datasheets of the dsPIC or the BT module.

 

[John Larkin]

I am making a new PCB where size and weight are critical. I would
like to drive two chips (a microcontroller and a Bluetooth chip) using
a single crystal oscillator. What is the effect of driving several
chips with a single oscillator? Is it possible?

Sure, but make sure that both chips get clean, fast edges, which means
that you've got to handle the trace routing, impedances, and
terminations properly. Even cheap XOs can have sub-ns risetimes these
days, and lots of cmos chips have very tender clock inputs. A little
ringing, or a half-level plateau and a bit of crosstalk, can cause
serious grief.

John

 

[Tim Wescott]

I'm wondering if the input capacitance of the chips affects the
oscillator. The oscillator has an optimal load capacitance that it
performs with. I can't seem to find the input capacitance information
in the datasheets of the dsPIC or the BT module.

That information should be there, buried in the 100s of pages of other
necessary information.

By the same token, though, if you can't be sure that two will work, how
can you be sure than one will?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Tam/WB2TT]

I'm wondering if the input capacitance of the chips affects the
oscillator. The oscillator has an optimal load capacitance that it
performs with. I can't seem to find the input capacitance information
in the datasheets of the dsPIC or the BT module.

If the oscillator has a logic level output, it will work with any load
within its fanout limits. If you are using the oscillator built into one of
the chips, and you want to use its output to drive the other chip, I would
put a gate of some kind near the source chip to buffer the output.

Tam

 

[Jamie]

I'm wondering if the input capacitance of the chips affects the
oscillator. The oscillator has an optimal load capacitance that it
performs with. I can't seem to find the input capacitance information
in the datasheets of the dsPIC or the BT module.

use a couple of unity gain stages to drive and semi isolate them.