TPS281C100: Odd response to EN toggling

Hi Ortal,

Are you trying to have the output always ON when the PWM is active? Or do you want EN to follow the PWM?

Can you just drive the EN pin with the PWM directly?

Thanks,

Patrick

The purpose of the design is to drive with actual PWM that would be filtered by the RC, and have the device on for a wide pulse, and off for a narrow pulse.
For the sake of the bringup, I can drive the EN directly, but it does not solve the issue of the thermal shutdown at 4.7A load:

Hey Ortal, 

Following up and will have a recommendation on 10/24.

BR, 

Alan

Hey Ortal, 

Are you using the EVM to test this application? In addition, are you using the GND network in this application?

For the sake of debugging can you try this at DC to eliminate any switching losses from the PWM.

BR, 

Alan

Hi Alan,

Thanks for your response.

I did not use an EVM. 

The last graph I attached was at DC, and as you can see the output shuts down.

Regarding GND network, could you specify what you mean?

Highlighted is the GND net, U1 is TPS281C100

Hi Ortal, 

Do you have an external current limiting resistor? It should align with the table below.

By GND network I am referencing the resistor -diode configuration to protect from reverse polarity. It is displayed below:

Best regards, 

Alan

Hi

Yes, I have a current limiting resistor, I have a jumper that allows me to choose the specific resistor according to expected current:

I didn't use a GND network because I use a directional connector.

Hello, 

I recommend trying this configuration on an EVM. This is within device operating parameters so there should not be an issue, especially when operating at DC. 

Best, 

Alan

Hi,

Thank you for your response.
I tried using a thermal camera and I notice that whenever the device reaches ~156C, it shuts down.

Do you have advice regarding the layout perhaps that might help?

Thanks in advance

Ortal

Hey Ortal, 

Are you able to share an image of the top layer layout? The datasheet has layout recommendations as well as thermal considerations in section 9.4.3.

Best, 

Alan

Hi,

this is my top layer layout:

Thanks in advance

Ortal

Hey Ortal, 

Maximize the copper coverage on the PCB to increase the thermal conductivity of the board. The major heat-flow path from the package to the ambient is through the copper on the PCB. Maximum copper is extremely important when there are not any heat sinks attached to the PCB on the other side of the board opposite the package.

Add as many thermal vias as possible directly under the package ground pad to optimize the thermal conductivity of the board.

BR, 

Alan