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Original question:
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Hi,
I am Designing a DC-DC Converter with LM5171-Q1, the converter will be operating as 2 phase Bidirectional Buck, Boost (In one direction Buck and other Direction Boost). I have designed the circuit based on the TI Application note details. I want to operate the converter both in Current mode as well as Voltage mode. I have set the feedback voltage FBLV and FBHV, also connected 2V at Vset point derived from Vref pin. Both the ERRLV and ERRHV connected to ISET point as per the application note schematic. Current will be setting through PWM Duty adjustment.
Now my question is i will be adjusting the Duty to the ISET pin for average inductor current settings, for example i have adjusted the duty for 30A inductor current, and output voltage is 14V, as per my understanding the output voltage will be 14V until inductor current reaching to 60A, Once the inductor current reached 60A , current will be constant and the output voltage will start reduce. in other words, i have set the duty for 30A channel inductor current at ISET pin, now my load is taking only 20A channel inductor current, then the converter should regulate the output to 14V until 30A, whether this understanding is correct? or i have to adjust any other settings to operate in constant voltage mode. What setting i have to do for operating my converter in 30A, 14V output current.
I will be connecting the circuits same way as above, if i am using the PWM Duty control for Inductor average current settings, how will be the ISET pin connection, whether i have to use the RISETT and RISETB resistors? or ERRLV and ERRHV directly we can connect to ISET Pin?
Please help by providing some details to understand the LM5171-Q1 operation in both Voltage mode and Average Current mode.
Regards
Rayees K E
Hi Rayees,
Your understanding is correct.
One simple way to achieve CC/CV regulation is clamping ISET voltage. In this way, the ISET voltage is regulated by the voltage loop till the current limit is reached.
On the EVM, by applying 2V at J43 (and short J42), the average current will be limited to (2V-1V)/40/1mohm=25A per channel.
Best Regards,
Feng
Hi Feng,
Thank you for your quick response.
Yes, I am limiting the ISET pin voltage by Digital control.
So, as per my understanding from your communication, no additional circuit is required, I can connect the digital signal to I SET pin for controlling the inductor current, Also, voltage feedback can be connected to the ISET pin directly without using the additional resistor divider. With this connection I will be able to set the inductor current limit and also regulate the output voltage when current is not reaching the CC limit.
As per below EVM Schematics,
With ISET PWM Input, ERRLV and ERRHV not connected to the Iset pin, then how the output voltage will be regulated?
Regards
Rayees K.E
