2
\$\begingroup\$

I am looking at the data sheet for the iC-NZN N-type laser diode driver.

iC-NZN-screenshot

What does the marked symbol stand for?

It appears in a number of places, always marking IO pins. My guess would have been that it is a current limiter, but then why not just draw a resistor...

\$\endgroup\$
  • \$\begingroup\$ Who provided the diagram? Did they provide a legend? Somewhere? \$\endgroup\$ – Solar Mike Aug 5 '18 at 9:13
  • \$\begingroup\$ I have never seen this symbol on a IC data-sheet before but on circuit before but on circuit diagrams for a PCB it is often used as a net-tie or star-point where to signals are routed separately then joined together at a single point. \$\endgroup\$ – Warren Hill Aug 5 '18 at 9:16
  • 3
    \$\begingroup\$ The symbol will normally be used for a current source. \$\endgroup\$ – keffe Aug 5 '18 at 9:18
  • \$\begingroup\$ @solar-mike I posted the link to the datasheet. It is issued by the manufacturer of the IC. \$\endgroup\$ – polwel Aug 5 '18 at 9:43
  • \$\begingroup\$ @Mathias They draw current sources the usual way (see just left of the CIS pin in the image I posted). A current source makes no sense in this context. \$\endgroup\$ – polwel Aug 5 '18 at 9:43
2
\$\begingroup\$

Here, it is only used for connections to power and ground.

I would guess, it is a low inductance connection with multiple wirebonds with the same effect as Litz wire. This is of great benefit to reduce ringing in pulsed lasers.

It is similar to a shielded signal but without a flat line below the circle.

\$\endgroup\$
  • \$\begingroup\$ Makes sense to me, thanks. Bonus question: why would I prefer to use such a presumably low-L connection to GND through the IC, rather than just large trace on the board? I am specifically talking about the RGND pin, not shown in the image I posted. \$\endgroup\$ – polwel Aug 5 '18 at 11:22
  • \$\begingroup\$ The RGND is not used for pulsed laser current so requirements are lower frequency noise and lower DC current over DC return. \$\endgroup\$ – Sunnyskyguy EE75 Aug 5 '18 at 11:43
  • \$\begingroup\$ Exactly, that's my point. It seems to me I could do the same, but better, with a separate trace. \$\endgroup\$ – polwel Aug 5 '18 at 11:47
  • \$\begingroup\$ CLDA needs low L connections to LDA and AGND to lower impedance (L/C) and raise resonant frequency ^2 =1/(LC) \$\endgroup\$ – Sunnyskyguy EE75 Aug 5 '18 at 11:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.