Electronics > Projects, Designs, and Technical Stuff
Case Study: SMPS fails at elevated voltage
brabus:
Bootstrap MLCC voltage rating?
Dulus:
From the datasheet:
--- Quote ---4 EN On/Off. Pull EN above 1.35V to turn the device ON. For automatic enable, connect to VIN using
a resistor. Note that make sure the sink current of EN pin not exceed 100μA.
--- End quote ---
Enable resistor not big enough? :palm:
PeteH:
The layout is always different.
FB routed next to switch node.... Weak ground connection...
T3sl4co1l:
--- Quote from: uer166 on July 21, 2020, 05:50:58 am ---First thing I'd look at is the schematic and then the layout, of which we have neither. This would be a lousy interview question.
--- End quote ---
It's not an interview question, it's to consider the possibilities -- and you've just found one.
--- Quote from: PeteH on July 21, 2020, 09:38:32 am ---The layout is always different.
...
Weak ground connection...
--- End quote ---
Ding ding ding!
You look at the layout. You find the ground return trace to the regulator is maybe 5mm. The VIN trace is about 20mm to the nearest capacitor. Both traces are 10 mil width. The board is 4 layer with inner planes, but the regulator extends out past the edge of the planes for some reason!?
What do you tell the engineer to do?
Tim
capt bullshot:
Solder an appropriate capacitor from VIN to nearest GND plane. 20mm to the next cap is too far, causing inductive kickback from the trace into the regulator.
Navigation
[0] Message Index
[*] Previous page
Go to full version