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PSoC 5, 3 & 1

AntoineBoubou
New Contributor

Hello,

I am currently working with a PSoC5LP (precisely CY8C5888LTI-LP097) and my application is meant to power 7 LEDs with PWM supply.
I designed a Pcb on which my MCU is clipped (thanks to connector headers that are soldered on each holes of PSoC). The MCU is powered by a 5V regulator (on VDD/Ground pins) and its function is to send PWM signals to LED drivers that will supply the LEDs (powered by the pcb supply at average 350mA of current and 2.75V of tension).

Moreover, I want to monitor the PWM duty cycle of the signals delivered by the MCU thanks to .net application.
The USB communication is possible thanks to the micro-USB connector which takes place on the target board.

The fact is I suppose I can not power at the same time the PSoC with USB and also an external source. 
So what are your solutions to avoid the two supplies to "kill each other" if it what will happen ?

I reflected about sth : what about if i desolder only vdd head connectors so that the external source is not seen anymore by the MCU, it would mean only the USB port Ground and the external supply ground will be in contact).
The second question is :
Is there a risk of ground loop with the current out of the leds ? I mean do the currents out of LEDs have a chance to go through the usb port ground instead of external supply ground ? Is there a risk for USB port to be damaged ?

I attach the pdf file which illustrate the pcb (supplied by 24V).

I am looking forward to hearing from you, thanks
Best regards,

Antoine

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1 Solution
Ekta
Moderator
Moderator

Hello Antonie,

The fact is I suppose I can not power at the same time the PSoC with USB and also an external source. 
So what are your solutions to avoid the two supplies to "kill each other" if it what will happen ?

Since you are using an external power supply to power the board I would suggest you to remove the D2 diode on the board so that the board is simultaneously not powered by the micro USB and the external power supply.

The CY8CKIT-059 user guide also mentions this "To use an external power supply, while KitProg is connected to the PCB USB, remove diode, D1, from the board. This ensures that VTARG supply from KitProg is not supplied to the target device. KitProg measures the target voltage and adjusts the logic levels on the programming pins
accordingly."
I guess in case of micro USB connection the diode D2 needs to be removed.
The schematic for the CY8CKIT-059 can be found at the following link.

Ekta_0-1626852191165.png



Is there a risk of ground loop with the current out of the leds ? I mean do the currents out of LEDs have a chance to go through the usb port ground instead of external supply ground ? Is there a risk for USB port to be damaged ?

I don't think there is a risk of the USB port being damaged. We recommend you to follow the PSoC 5LP Hardware consideration guidelines while designing your board.

Thanks 
Ekta

View solution in original post

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1 Reply
Ekta
Moderator
Moderator

Hello Antonie,

The fact is I suppose I can not power at the same time the PSoC with USB and also an external source. 
So what are your solutions to avoid the two supplies to "kill each other" if it what will happen ?

Since you are using an external power supply to power the board I would suggest you to remove the D2 diode on the board so that the board is simultaneously not powered by the micro USB and the external power supply.

The CY8CKIT-059 user guide also mentions this "To use an external power supply, while KitProg is connected to the PCB USB, remove diode, D1, from the board. This ensures that VTARG supply from KitProg is not supplied to the target device. KitProg measures the target voltage and adjusts the logic levels on the programming pins
accordingly."
I guess in case of micro USB connection the diode D2 needs to be removed.
The schematic for the CY8CKIT-059 can be found at the following link.

Ekta_0-1626852191165.png



Is there a risk of ground loop with the current out of the leds ? I mean do the currents out of LEDs have a chance to go through the usb port ground instead of external supply ground ? Is there a risk for USB port to be damaged ?

I don't think there is a risk of the USB port being damaged. We recommend you to follow the PSoC 5LP Hardware consideration guidelines while designing your board.

Thanks 
Ekta

View solution in original post

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