UCC256403: About the timing to apply VCC

Kaji@PAN

Part Number: UCC256403
Other Parts Discussed in Thread: UCC28180,

Hello,

I am considering using UCC256403(LLC) and UCC28180(PFC).
I would like to ask you about when to apply the VCC of UCC256403 at startup.
In order to avoid overlapping the timing of the inrush currents of PFC and LLC at startup, we plan to start LLC after the output voltage of PFC is completely stable.
In this case, as the operation of LLC, it is assumed that 13V is applied to VCC after the voltage of the BLK pin exceeds the start threshold value for a while.
This state is when the BLK voltage reaches the BLKStart level before the VCCStartSwitching threshold is exceeded.
Is this behavior possible?

Best regards,

over 3 years ago

0 Manikanta Pallantla over 3 years ago

TI__Genius 16155 points

Hi Kaji,

The following schematic will help you to understand the startup procedure for both of the devices that you are trying to use.

TIDA-01494 Schematic and Block Diagram (Rev. A)

In this schematic (In general), LLC will start after PFC establishes its output voltage to its rated value(BLK pin voltage > BLK threshold). So, even if you apply 13V at the start to both the controllers, LLC will start switching only when BLK pin voltage is more than threshold which would eliminate the inrush currents.

Regards

Manikanta P

0 Kaji@PAN over 3 years ago in reply to Manikanta Pallantla

Mastermind 7785 points

thank you for your reply.
I have already confirmed the above contents.
In the System State Machine, I want to know if it is okay if the BLK voltage exceeds the BLKStart level before the VCCStartSwitching threshold is exceeded.
Best regards,

+1 Manikanta Pallantla over 3 years ago in reply to Kaji@PAN

TI__Genius 16155 points

Hi Kaji,

Kaji@PAN said:
In the System State Machine, I want to know if it is okay if the BLK voltage exceeds the BLKStart level before the VCCStartSwitching threshold is exceeded.

If you do this startup time will reduce. So, I don't think there will be any issue.

Regards

Manikanta P

Power management

Power management forum

UCC256403: About the timing to apply VCC