Part Number:LM2907-N
I have built a circuit based on the "minimum component tachometer" diagram on the first page of the spec sheet for the LM2907 freq. to voltage converter. I have observed a strong sensitivity to temperature for this circuit at a fixed input freq. despite the spec. sheet indicating the chip is reasonably insensitive to temperature. I tested this by quickly poitning a hot air gun at the chip and it rapidly drops a couple of voltage on teh output signal. I tried to shield the external components (capacitors) and just heat the chip and it still seems to change? Is there a reason the chip is so sensitive to temperature? In addition to the components in the diagram, I use a 4uF series capacitor and a 1k resistor to ground to "AC couple" the input such that the converter (that requires zero crossings) will work with a square wave that swings 0-12V (never goes below zero). I do not need a very wide operating temperature range (about 30F to 120F). The signal I am converting is 150Hz or lower. The fmax for the components used should be about 1000Hz.