+1 to Ruben and to add what to what he is saying by means of a graphic:
An engine is able to take in a certain amount of air at a given RPM, regardless of the turbo attached to it, as shown by the pink curves. Taking the 4000 RPM line for example, raising the RPM of the turbo (requesting more boost pressure) moves you up along the 4000 RPM line towards higher mass flow and pressure ratios and the shaft RPM is where the pink line intersects with the dark blue curves with labels at the right-hand side. So this particular turbo matched to the engine spins at 139998 RPM at just under PR=2 (about 14.5 PSI) / 15.5 lb/min, and at 179x99 RPM operates at about PR=2.65 and 20 lb/min.
You will note, however as you get toward the right side of the map, the curves of constant RPM bend down. This means that increasing the RPM is not accompanied by a proportional increase in mass flow. This is the choking that Ruben mentioned.
Turbochargers are rated to certain "tip speeds". This is calculated by V=r*omega (omega is the angular velocity in radians per second). This is equal to V=r*(2*pi*RPM/60). A modern turbo is able to withstand about 520 m/s beyond which efficiency drastically decline and may also exceed the structural strength and creep resistance of the wheel design and materials. This limit is constantly moving upward with improving technology of the latest generation turbos; for example, the Borg Warner EFR series can do 580 m/s and may be even higher with even more recent turbo designs.
For a 52mm exducer compressor wheel, r=0.026m, so the maximum RPM is 60*V/(2*pi*r) or 190986 RPM. Assuming a pretty recent design, a 60mm compressor with 560 m/s tip speed limit gives a max. RPM of 178253 RPM and this limit should be respected for good reason!