1) Instead of 2.5v (adc) = 0 amps, I want 0v (adc) = 0 amps.
2) I also want to stretch the range of the ACS712 so that 0v (adc) = 0 amps and 5v (adc) = 15 amps.
I want to do this using only a +5vdc supply, not a +/- bipolar supply.
..Instead of using an LM35 I recommend to use ADC_Ref. ...
ACS712 zero is specified at Vcc/2, no matter if supply voltage is stable or not. Using Vcc/2 as "reference" is thus correct in any case. Subtracting "stable" 2.5V reference from unstable Vcc/2 zero sensor output would introduce an additional error term.In case you have a stable and clean true 5V reference voltage, then you could simplfy your circuit:
Don't use the first Opamp, just replace R1 with two 20k resistors, one to GND, the other to Vref.
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