This paper proposes a voltage-limited finite-settling-step direct torque and flux control (FSS-DTFC) method with a constant switching frequency for torque-controlled interior permanent-magnet synchronous motors (IPMSMs). The proposed control law dynamically scales voltage vectors on the hexagonal voltage boundary to ensure maximum torque capabilities at given operating conditions, while simultaneously regulating the stator flux linkage magnitude under flux-weakening operation. Instead of evaluating control performance based on intuitive voltage selection rule, this paper focuses on developing a discrete time function of the rate of change of an air-gap torque for facilitating optimal voltage vector choices. Then, this analytical solution leads to optimal voltage modification at each time step with respect to the available inverter voltage. The voltage-limited FSS-DTFC approach has potential advantages of achieving fastest transient torque trajectories and direct manipulation of the stator flux linkage while exploiting maximum voltage excitation.