PMP22764: Layout difference

Dice-K,

All of the drawings on the website are Rev B, including the test report.  The testing was done with a Rev A PCB modified to Rev B component values.  The PCB was updated to Rev B to meet a specific customer's size requirements.  The Rev B PCB was tested and had the same electrical characteristics as the Rev A PCB modified to Rev B component values.  Both PCB layouts worked ok.  I'll look into updating the test report with a new photo and thermal images of the Rev B board.

Thanks,

David

Dice-K,

Yes, components can be mounted on both sides of the PCB.  I would recommend a 4 layer or more PCB.  This will allow at least one layer to be solid copper to provide shielding between components/traces on the two PCB sides and other layers.  Do not place components/traces below the primary FET Q1 or the secondary rectifier D1.  Both of these components are switching relatively large voltages and can be noisy.  They also dissipate power and can get hot.  R2, R4, R10 and R14 also dissipate power, so take this into consideration when placing them or other components around them.

The LM51561 is best for a flyback converter since it has the hiccup mode short circuit protection.  If you wan the option of using either IC, there is only one pin that is different.  You can use a couple of 0 ohm resistors, one POP, one DNP,  to allow the use of either IC.

Thanks,

David

Dice-K,

I misread the part numbers.  The LM5156 and LM51561 have the same pinout.  The only difference is the LM51561 has the hiccup mode short circuit protection.  The LM5155/51551 (which do not include the frequency dithering) have one pin different from the LM5156/51561.  If you want the option of using the LM51551 or LM51561 you can add 0 ohm resistors to pin7.  One should connect to ground and one to VCC.  For the LM51551 pin 7 is ground, so connect the 0 ohm resistor to ground.  For the LM51561 pin 7 is dither control.  Connect the 0 ohm to VCC to disable dither or connect the 0 ohm to ground to enable dither.  Sorry for the confusion.

Thanks,

David

Dice-K,

Yes, that is correct.

Thanks,

David