What controls the inter-block interval in proof-of-stake?

In proof-of-work, the interval between 2 blocks is controlled by the mining difficulty: at all times, it must take roughly 10 minutes to mine a block, so every two weeks we adjust the mining target accordingly.

However, in proof-of-stake, it takes a few seconds at most for a staker to verify and sign a block, so what prevents proof-of-stake systems to be flooded by a ton of new blocks every minute?

Thank you for your help.