Hi Team,
For page 10 of https://www.ti.com/lit/ug/slou449/slou449.pdf, there are two resistors R6/R11 after two stages RC filters.
What's the use of these two resistors and how to choose the value. Thank you!
Marc
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Hi Team,
For page 10 of https://www.ti.com/lit/ug/slou449/slou449.pdf, there are two resistors R6/R11 after two stages RC filters.
What's the use of these two resistors and how to choose the value. Thank you!
Marc
Hi, Marc,
I don't have much details on this, but it seems that the resistors R6 and R11 are used as part of the input filter to reduce the input level. I think it is used as a device protection for the PWM external level.
Please take a look at the captures below for details on the input filter frequency response with and without the resistor.
Input filter with resistor:
Input filter without resistor:
I also attached the TINA simulation in case it is required.
Best regards,
Luis Fernando Rodríguez S.
Hi Luis,
Thanks for the reply!
I agree it can work as protection to reduce the input level with two stage filters. But from page 4 of http://www.ti.com/lit/ug/slou449/slou449.pdf, Figure 4 shows when J6/J9 is shorted, only 3.3k ohm res is on the wire.
Customer wonders if this is must if they don't need the RC filters. Thank you!
Marc
Hi, Marc,
The low pass filters are required for PWM input only. The idea of this filter is to reduce/eliminate all the high frequency content, which is not necessary in the device application.
Best regards,
Luis Fernando Rodríguez S.
Hi Luis,
Sorry, I didn't say it clearly. What I mean is when no RC filter, is the 3.3k ohm pull down resistor still needed?
Thank you!
Marc
Hi, Marc,
Understood. The pull down resistor is not needed in this case. This is just a security connection for our EVM in order to avoid damage due to external voltage level. You may omit this resistor but just ensure that the absolute maximum ratings are not reached.
Best regards,
Luis Fernando Rodríguez S.