DAC161S997: Increase loop current, speed

yoko19298

Intellectual 395 points

Part Number: DAC161S997

Hello,

I have few questions regarding DAC161S997

1. Increase loop current

Speaking of datasheet

Figure 15. Loop-Powered Transmitter --> ILOOP = (1 + R1 / R2) IDAC
Figure 16. Self-Powered Transmitter --> ILOOP = 24 mA (DACCODE / 216)

For loop powered, one can override R2 (lower) by adding a extra R over COMA/OUT pins for increase current (I need maximum 2A). This is correct?
How can I increase current in self powered scheme?

2. Loop speed

What is the maximum speed of loop? I need about 100KHz (100Kbps) to be transmitted, presume this is related to DAC only.
What kind of transistor will be suitable for this speed and current.

3. Minimum current

Normally I will need a 1mA minimum current, but I guess 4mA will be fine. There is a method to decrease this?
I saw it depends on IE or other currents involved in loop.

4. Part

If the part is not suitable, can you recommend me another solution?
I am thinking of regular SPI DAC + OA + MOSFET as a digitally controlled load but I am not sure of complexity and costs vs. speed, etc

Thank you in advance,

over 9 years ago

0 Paul_Frost over 9 years ago

TI__Guru 57453 points

Hello,

I am not sure that the DAC161S997 would be the best solution for the application. Specifically your comment about the loop speed raises some concerns. The DAC161S997 utilizes a ΣΔ architecture, which has limited rate of change. Figure 4 describes the settling time performance of the circuit. In addition, this device 'creates' a local GND (COMD and COMA) that maybe present some additional isolation issues.

I think your DAC, amplifier, and FET as a controlled load is good idea that will allow you to adjust the circuit as needed. A good starting point would be to look at the following guides:

TIPD101

TIPD102

Great discussion about current sinking

Another good discussion

Let me know if you have any specific questions about the design!

Thanks,

Paul