Hi E2E,
1. Why the IMPS is 16mA?
I think that system load is =12mA, so we need to add 16mA let total = 28mA to meet Automatic MPS SPEC, right?
2. Could you kindly check RMPS formula "VDD" is typo or not?
I think that is 24V not VDD, otherwise VMPS should be 57V not 24V.
3. Why that when I got the RMPS = 3.56k ohm, next step go so far as 1.3k ohm??
4. When we calculate the total P to choose suitable resistor, should I consider the duty cycle?
Thanks!
Hello Julian Chen,
Thank you for your question, and for bringing this to our attention. First, let me just say this equation has several issues, which is causing confusion. I apologize for all confusion and any delays in projects due to this.
Below I captured the correct equations, as found in the TPS2372 datasheet.
http://www.ti.com/lit/ds/symlink/tps2372.pdf
As you can see, it is not VDD but V_AMPS_CTL.
IMPS is now 18.5mA to match Table 5. If your system has a 12mA load already, then you can design IMPS for 6.5mA to meet the overall 18.5mA load requirement.
In our calculations we include duty cycle into our power calculation. We have tested 1/8W resistor in our designs and have not had any issues with it.
We will work to correct the TPS2373 datasheet to reflect the correct values. Thank you again for your comments!
Regards,
Michael Pahl
