I built a simple circuit to produce -5V from regulated +5V but it doesn't work unless the voltage is at least +6.5V as input.
- The LT1054C shoud work ok from 3.5V but I measure 0V at output with my multimeter when Vin is +5V.
- If I raise Vin to +6.5V, the Vout is -6.5V and my circuit works normally. Seems that 6V is the minimum to get the negative voltage output.
- from the datasheet, the switching frequency of the DC DC step down LM2596 is 150 KHz while the LT1054C can be configured between 15 and 35 kHz. So it impossible to sync both. I think the issue could be here maybe?
- I use tantalum capacitor (marked "Ta"). Other are Al standard cap. I followed the LT1054 datasheet. I tried Cin=Cout=100uF (tantalum) too.
(I bypassed the problem by using 7805 and 7905 regulators in each corresponding inputs but it's ugly)
Why can I get directly the -5V from the +5V?
I will be using 12V unregulated input and regulation to -5V.
It is still not working. I measure Vout = +0.4V with Vin=+12V. It's curious that Vref=+7V while it should be +2.5V (internal reference). I tried a second chip (LT1054C N8 by Linear Tech.), same thing. Both chips work fine as simple inverters (no resistors, Vout=-Vin if Vin>+6.5V)
I tried a LM336-2.5V reference as external reference instead of using the reference pin, same thing.
Breadboard circuit: [link]https://drive.google.com/open?id=1Rgna1OPtDUJwWGj8AU4rmA7glmsUp6G5