What happens when the ENABLEA or ENABLEB pin is open?
For example, can you tell me if the output is fixed at 0V or not?
Sorry but I did not notice your post until now. Apologies.
Regarding the LTC6420-20 ENABLE pins:
Here is what the datasheet states: "ENABLEA, ENABLEB (Pins 9, 18): Logic inputs. If low, the amplifier is enabled. If high, the amplifier is disabled and placed in a low power shutdown mode, making the amplifier outputs high impedance. These pins are internally separate. These pins should not be left floating."
So, as stated, these pins should not be left floating / open. Leaving them floating may leave the device in an undetermined condition.
When disabled (Enable pin tied High), the output(s) are high-impedance.
Hope this answers your question.