The HMC1060 output remain ON, even when the enable input is pulled down.
The enable is driven from a GPIO line of Processor, whose maximum output is 3V3.
So there is no chance of damaging the EN pin.
Another IC in the same board is working correctly.
Sorry to hear your having difficulties with the HMC1060 quad regulator.
First I'd verify the voltage at the EN pin with the GPIO attempting to pull it low using a high impedance probe. The HMC1060 uses TTL logic so a logic low must be less than 0.8V otherwise the HMC1060 will remain on. Without a schematic and seeing how the 'working' HMC1060 is connected it's hard to say why one works and the other doesn't. Perhaps there's something on the board (either planned or unplanned) that is preventing the processor from pulling it low. I highly recommend that you verify that any voltage overshoot/ undershoot on the EN pin falls within the limits outlined in the AMR table on page 5 of the datasheet. If it turns out that the existing device is actually damaged you may need to repeat this with a new part. I would duplicate this effort on the working HMC1060 as well. Next I would temporarily bypass the GPIO logic and physically short the EN pin to ground and see if the device responds in the expected manner. Note that the cap on the REF (pin 4) makes a difference in the rate (time constant) at which the HMC1060 will cycle on / off and there is a trade off with respect to the noise particularly beyond 100 kHz. This is also discussed in the datasheet. If all else fails install a new device being sure to use good ESD handling practices and see if that makes a difference.
We had to replace the device. Now it is working properly.