TOP258PN frequency problem
We use a TOP258PN in a standard flyback application.
We noticed that suddenly at a production batch of 100 pcs., at 8 pcs. the switching frequency is outside the specified range: we measure 52.2KHz instead of the minimum specified 59.4KHz.
We also noticed that by changing the control current (by means of varying R471) the frequency changes also.
What can be the reason, and how can this be solved?
In the attached schematic, R451 is not stuffed, and R452 and R454 are zero ohm.
Comments
Thank you for your reply.
The specified min. switching frequency is 59.4KHz with a +/-2.5KHz jitter, see the attached datasheet.
So, we test our products based on this specification.
We are working with a frequency sensitive application, so we want to know where the frequency is.
According to the datasheet, the minimum should be 59.4-2.5=56.9KHz, but we measure below this.
Does this mean that this minimum of 59.4KHz on page 32 of the datasheet is also a typical value?
Hi,
What is the test conditoin when you record the switching frequency, line voltage and load condition. Would you please check how much is the peak drain current under the test? Is there any difference between drain peak current between the 8 pcs and the other 92 pcs?
Hi,
If you refer the data sheet of Top switch, the switching frequency will change according to the load condition. Please refer the the figure 9 from the data sheet. So the minimum switching frequency is not specified at 59.4kHz. Moreover, there is a frequency jitter added in the switching frequency to help for EMI performance, the switching frequency will be slightly different between board to board and part to part because of the jitter. Do you see any critical issue because of having a little bit lower switching frequency? Is the power supply still operating?