Enlarge the number of sensitive pixels put in an instrument is a classical way to improve observatories. From cosmology in the millimeter range to high-energy astrophysics space instruments, the readout of thousands of cryogenic detectors requires dedicated electronic developments. Application-Specific Integrated Circuits - ASICs offer major advantages in this context: specific design, small size and optimized performances. In addition, consumption is kept to a minimum, and the hardening by design can protect against the effects of radiation and thermal drifts faced in space.