Hi Lixing,
1) The device has over current protection which trips at 7.5A. It will shut down (output goes to high Z) if the output current exceeds this current limit, but this is determined by the output current and not directly by the input voltage level. The device has protection circuitry outlined on page 14 of the datasheet.
2) I do not see a common mode choke at the output. However, the two caps from the two sides of load to ground you referred to are part of the output filter along with the inductor. The "OUTPUT FILTER CONSIDERATIONS" section of the datasheet provides some info for how the choice of cap value affects the filter. This app note is from our audio team, but provides some more detail on this type of filter www.ti.com/.../sloa119b.pdf
What is your application for this part? This will have an effect on filter choice.
3) The need for filters will depend on the application and how you are wiring the output. Would you be able to provide some more details? It is worth noting that in 1spw the bottom half bridge is switching when there is no output and is usually not switching when there is output. In normal applications like a TEC driver I believe you need both inductors.
4) I wanted to clarify the questions from my previous post before commenting on what is causing the problem as I wasn't sure about your answers to them.
Are you following the start-up sequencing from the datasheet? - It sounds like you changed the setup to meet the spec but still have the issue. Is this correct?
How are you generating the 3V applied to IN-? - It sounds like you changed to a differential input and removed the 3V, but still see the issue. Is this correct?
When the device fails to turn on what is the voltage on the fault pin? - I didn't see an answer to this in your last post. If I missed it could you please let me know.
Have you tried this on the EVM? Do you see the same problem?
Regards,
Alex
1) The device has over current protection which trips at 7.5A. It will shut down (output goes to high Z) if the output current exceeds this current limit, but this is determined by the output current and not directly by the input voltage level. The device has protection circuitry outlined on page 14 of the datasheet.
2) I do not see a common mode choke at the output. However, the two caps from the two sides of load to ground you referred to are part of the output filter along with the inductor. The "OUTPUT FILTER CONSIDERATIONS" section of the datasheet provides some info for how the choice of cap value affects the filter. This app note is from our audio team, but provides some more detail on this type of filter www.ti.com/.../sloa119b.pdf
What is your application for this part? This will have an effect on filter choice.
3) The need for filters will depend on the application and how you are wiring the output. Would you be able to provide some more details? It is worth noting that in 1spw the bottom half bridge is switching when there is no output and is usually not switching when there is output. In normal applications like a TEC driver I believe you need both inductors.
4) I wanted to clarify the questions from my previous post before commenting on what is causing the problem as I wasn't sure about your answers to them.
Are you following the start-up sequencing from the datasheet? - It sounds like you changed the setup to meet the spec but still have the issue. Is this correct?
How are you generating the 3V applied to IN-? - It sounds like you changed to a differential input and removed the 3V, but still see the issue. Is this correct?
When the device fails to turn on what is the voltage on the fault pin? - I didn't see an answer to this in your last post. If I missed it could you please let me know.
Have you tried this on the EVM? Do you see the same problem?
Regards,
Alex