A virtual synchronous generator (VSG) control for converters has been proposed as a method to provide virtual inertia from power electronics connected generation and storage. Most works to date have analyzed VSG control under the assumption that the VSG dynamics are much slower than that the converter. This work shows that when converter and line dynamics are taken into account, the virtual inertia and damping settings are constrained by stability considerations. These conditions for stability are analyzed based on a simple transfer function approach. It is shown that for the VSG to be stable and validly approximated by a second-order system, the ratio of damping to virtual inertia is a key parameter. This letter quantifies how these VSG parameters are constrained by stability. The transfer function analysis is validated using full switching model simulations of stable and unstable cases.