Maximum Vout for LNK3204 in Buck?

Hi Treez,

Thank you for reaching out to Power Integrations. 

There are several factors that can affect the maximum output voltage we can set in LinkSwitch-TN2. I highly suggest inputting all the parameters in the PI-XLs such that there won't be warnings in terms of its electrical parameters. The most critical parameter is the soft-start, other comments are in terms of other design considerations.

1) Soft Start - The LinkSwitch-TN2 device's start-up behavior operates such that after 50mS, the output voltage must reach its regulation threshold by monitoring the current being injected to the FB pin. If the output voltage didn't reach its regulation after the soft-start timer, the device will enter auto-restart. During these cases such that the high output voltage is not being reached after 50mS, a soft-start capacitor is required.
2) Thermal Management - While high output voltage is possible, the device is still limited in terms of output power. The LinkSwitch-TN2 device is recommended for operating below 12W, anything above may lead to issues with managing its thermal performance. 
3) Output Voltage protection - To ensure that there is protection due to high output voltage, it is highly recommended that you put an OVP circuit in the schematic. Since the output voltage is high, you will also require a higher rating of Zener Diode which also means higher leakage current. This higher leakage current also means that the regulation in the knee voltage have higher tolerance which can affect the reliability of the OVP Circuit unless a very tight tolerance of Zener Diode is used.
4) No-load input power - Since this is a high output voltage, we also expect a wider swing even if the tolerance is only 5%. This means that the current being injected into the BP/M pin will also swing if ever you have an external bias resistor connected to the BP/M pin. A precise current source may be required if you need a low no-load input power.

May I request for your design specification so that I can replicate it and check which are the critical parameters that must be considered.

Thank you.

Regards,

Thanks, we only need 15V and 100mA. Vin is 400Vdc.

Hi Treez,

I don't see any issues with that specification.  I'll provide the datasheet and design guide for your reference.

an-70_linkswitch-tn2_design_guilde.pdf (power.com)

linkswitch-tn2_family_datasheet.pdf (power.com)

Thank you.

Regards