DAC5672 / 50Ω doubly-terminated transformer configurations with 1:1 impedance ratio

K.Yaita

Other Parts Discussed in Thread: DAC5672

Hi Team,

The datasheet (page.18) shows "Applying a 20-mA full-scale output current would lead to a 0.5-VPP output for a 1:1 transformer", however I couldn't catch how to calculate to 0.5-Vpp.
Could you explain how to calculate to 0.5-Vpp?

I apologize if it is elementary question..
Your support would be appreciated.

Best Regards,
Yaita / Japan disty

over 9 years ago

0 Neeraj Gill over 9 years ago

TI__Mastermind 20541 points

HI Yaita,

Here is the link to the app note which discusses passive termination for current souring DACs. Section 2.2 of the app note explains your question in detail.

www.ti.com/.../slaa399.pdf

Regards,

Neeraj Gill

0 K.Yaita over 9 years ago in reply to Neeraj Gill

Guru 29720 points

Hi Neeraj-san,

I really appeciate for your support.

I understood the effective impedance is 12.5Ω.
Does "the effective impedance" above correspond to the following RLOAD?
I believe it but would like to confirm just in case.

(datasheet page.16)

Best Regards,
Yaita

0 Neeraj Gill over 9 years ago in reply to K.Yaita

TI__Mastermind 20541 points

Yes Yaita-san,

Your are correct. effective impedance corresponds to Rload.

Regards,
Neeraj Gill

0 K.Yaita over 9 years ago in reply to Neeraj Gill

Guru 29720 points

Hi Neeraj-san,

Thank you for your answer.
I would like to ask additional question.

I understood applying 20mA full scale lead to 0.5-Vpp output for the following schematic.
If my customer wants 0.6-Vpp output, which value should be changed?
Is it possible to change the 50Ω terminated resistor(red part) to 200Ω to achieve it?

Best Regards,
Yaita

0 Neeraj Gill over 9 years ago in reply to K.Yaita

TI__Mastermind 20541 points

Hi Yaita,

Yes 200ohms should be fine. 200ohms would make load on Iout1 and Iout2 = 200||50||25 => 15.38ohms. Using that to calculate max voltage on Iout1 & Iout2 = 15.38ohms*20mA = 0.30V This is well within the compliance voltage of the DAC5672 (–1 V to 1.2 V).

Regards,
Neeraj Gill

Data converters

Data converters forum

DAC5672 / 50Ω doubly-terminated transformer configurations with 1:1 impedance ratio