UDN2953B

The UDN2953B has the following features including 50V output voltage rating;2A continuous output rating;internal flyback diode;thermal shutdown;brake,enable and current-limit functions.

The UDN2953B is designed for bidirectional control of do or stepper motors with continuous output currents to 2 A and peak start-up currents as high as 3.5 A. For pulse-width modulated (chopped-mode) operation, the output current is determined by the user's selection of a reference voltage and sensing resistor while the OFF pulse duration is set by an external RC timing network. PWM operation is characterized by maximum efficiency and low power-dissipation levels. Extensive internal circuit protection includes thermal shutdown with hysteresis, transient-suppression diodes, and crossover current protection.The UDN2953B full-bridge motion control ICs are designed for pulse-width-modulated (PWM)bidirectional interface to many types of do (brush) servo, brushless dc, and 2-phase stepper motors. These power ICs permit various techniques of direct motor interface and offer internally and externally programmed current control. Pulse-width-modulated output current can be regulated by an (external) PWM control signal or use of an external sensing resistor (RsENSE) in combination with an RC network and/or voltage reference.

The motor is braked by simultaneously activating both source driver outputs and disabling both sink outputs. Basically, this shorts both terminals of the motor winding to the supply. The back EMF (electromotive force) of the motor develops current which functions as a dynamic brake. Typically, the braking current approaches the values related to a locked rotor (or stall) condition. Fundamentally, locked rotor (or stall) current is dependent upon the motor winding impedance and driver output ON characteristics. Internal current control circuitry is not operational during braking. Therefore, designers should exercise caution to ensure that the current produced by the back EMF does not exceed the absolute maximum ratings of the power outputs.In bidirectional drive applications, especially do (brush) servos, the PHASE input is utilized for direction control. The current generated by back EMF at reversal is comparable to that of dynamic braking, and should be limited to the absolute maximum output current rating.