LT1054 doesn't start when using SYNC pin

Thread Starter

Jorj

Joined Sep 30, 2015
19
I'm trying to synchronize LT1054 charge pump from external source. Normally this should work but in this instance the sync signal is comming from MCU which is powered by the +5V generated by LT1054. So right now when the pin is connected to the sync pin the +5V is not produced, the MCU doesn't start. Ideas how to fix this?

sync.png
 

Thread Starter

Jorj

Joined Sep 30, 2015
19
It's 12V. And I've just tested it - the resistor 20K between pin 6 and 7 (no Q1, R3) is enough to trip it (so it doesn't start), I wonder if I got a deffective part.
 

Thread Starter

Jorj

Joined Sep 30, 2015
19
yes, and I tried few different solutions, none of them worked. At this time I would probably change the schematic so the MCU is driven from fixed voltage source and use level shift, unless other solution pops up ;)
 

Thread Starter

Jorj

Joined Sep 30, 2015
19
It should be like that - its working as voltage doubler (GND on the schematic is +12V, +5V is actually +17V).
Because I needed a quick fix in order to submit new PCBs order fast (right now there's a sale 5$ for 10pcs with DHL shipping..)
I've powered the MCU from other fixed voltage +5V source, ofcourse problem is gone.
 

Thread Starter

Jorj

Joined Sep 30, 2015
19
No, it's actually positive voltage doubler. And it works. Your reference is for negative voltage doubler.
 
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