Buffer for a DAC 5

[jamesnguyen]

Hi,
I am using a DAC to control the voltage applied to "Iset" of a white LED driver IC (Onsemi CAT4104). Unfortunately, the DAC does not have enough current driving capability the CAT4104 requires (about 1mA).

I think I will need a buffer for the DAC. An Op-Amp buffer will do the job, but I am wondering if there is any cheaper, simpler transistor-based implementation out there?

Regards,
James

 

[VEBill]

Some organizations will have a policy of minimizing the extent of the design change for component obsolescence. They want to replace the obsolete part, and as few other surrounding components as possible, due to the extreme cost impact of change. It's often not an option to shift to a completely different architecture. Such seemingly logical 'major' design changes might invoke a complete requalification program costing six figures and a year.

If the LEDs are just used for human interface panel lighting, then the strict accuracy might not be a requirement. There would probably be Min = fully off, and Max = some defined brightness. But there might be enough flexibility in the requirements to simply use a transistor to increase the current, something like an emitter follower.

 

[jamesnguyen]

Hello All,

Just a quick update here. With an op-amp buffer, the backlight circuit works as expected and performs similar to the EOL part. So this is great!

VE1BLL,
Thank you for understanding! This is the exact situation I am in. I don't think it will cost us "six figures and a year". But it will delay the project launch about 4 months or so.

MacGyverS2000
Q: "Why would you ever control LEDs this way...? "
A: Why would many companies (Fairchild, Sipex, Exar, etc) want me to control their LED driver this way? Check out figure 1 of this link.

http://www.fairchildsemi.com/ds/FA/FAN5611.pdf

Best regards,
James

Many companies

 

[itsmoked]

jamesnguyen; Good going.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

James,

Let's be fair... at the time that comment was made, you had not told us your design parameters were severely restricted because the company chose to keep the design changes to a bare minimum. There are other/better ways to do what you did if you had proper control of the design...

Dan - Owner

http://www.Hi-TecDesigns.com