You can still use an ASIC with a PoS coin, it just doesn't benefit you as much. PoS coins still perform work on a blockchain with cryptography, but there is no

You can still use an ASIC with a PoS coin, it just doesn't benefit you as much. PoS coins still perform work on a blockchain with cryptography, but there is no reward to be the fastest. An ASIC for a PoS would allow you to lower the power requirements(Wattage and compute) of the machine running the PoS coin.