Other Parts Discussed in Thread: LM74910-Q1
Tool/software:
I'm working on a design using the LM74900-Q1 or LM74910-Q1 in a priority MUX configuration, based on the example circuit in the application note that includes the HGATE boost transistor.
I’m trying to achieve a fast turn-on time (around 20 µs total like in the app note, including the deglitch delay) because I don’t have space for large output capacitors to hold up the voltage during switchover. To help with this, I’ve added the recommended external boost stage on HGATE, using a transistor fed from the CAP pin. I’m curious how much current I can realistically push into the MOSFET gate with this method?
Can you clarify:
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What is the realistic max current I can draw through the boost transistor without interfering with the charge pump startup or CAP regulation? Is there an internal limit I should stay under to avoid instability?
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Is there a recommended maximum output capacitance that the LM74900-Q1 or LM74910-Q1 can reliably charge through the HGATE FET during initial power-up? I'm not very worried about startup time just the switch over from primary to secondary and secondary to primary.
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What is the limit to how large the capacitor is on the cap pin? Is it at all possible to get 5ma or more during turn on of HGATE with the boost transistor?
Appreciate any guidance you can offer here. Thanks in advance!
