Power Electronics

Full-Bridge PWM Gate Driver ICs

Allegro MicroSystems, LLC introduces a new family of full-bridge gate driver ICs designed to drive a wide range of DC brushed motors with simple logic from a microprocessor. The A4955, A4956, and A5957 devices can support motor supply voltages up to 50 V and load currents of up to 20 A. These devices are targeted for both the industrial and consumer markets in applications such as robotic vacuums, vending machines, cash dispensing machines, coffee vending machines, ticketing machines, automatic gates and turnstiles, and sewing machines.

Flexible interface options are offered in three individual products which means there is a product that will fit into designers existing solution with little or no firmware changes:

a. The A4955 offers parallel control [IN1, IN2, SLEEPn] which drives the bridge in forward, reverse, brake, and standby.

b. The A4956 offers Phase, Enable, and Mode inputs which drives the bridge in forward, reverse, brake, and fast decay.        

c. The A5957 offers Phase, Enable, and SLEEPn inputs which drives the bridge in forward, reverse with slow decay SR.

Unique features of the A4955, A4956, and A5957 include AIOUT function. This analog output can be used to monitor current through the external sense resistor (if used). A sample-and-hold is used to capture the peak voltage across the sense resistor and hold that value during the off time until the next PWM cycle begins. The voltage is gained by a factor of 10 and fed to the AIOUT terminal providing the customer the ability to accurately estimate the current in the load in real-time. Another unique feature is the programmable gate drive. An external resistor sets the magnitude of the current into the gates of the external FET bridge, allowing the designer to control the slew rate of the driver to help achieve EM compliance.

Other key features include internal pulse width modulation (PWM) current control. Peak current is regulated with a fixed off-time PWM regulator, the peak current is selected by the voltage on the VREF terminal. In addition an overcurrent flag notifies the user when the device is actively PWM limiting the current in the load.

Protection features include VDS sensing. Monitoring the VDS of the external MOSFET provides protection in case of bridge/motor shorts. Undervoltage lockout prevents the need for power sequencing, cross-over current protection for driving wide range of FETs and thermal shutdown. The A4955 and A4956 devices are supplied in a low-profile 4x4 mm, 20-contact QFN package (suffix ES) as well as in a 20-lead eTSSOP (suffix LP), both with exposed power tab. The A5957 is only supplied in the low-profile, 4x4 mm, 20-contact QFN package (suffix ES) with exposed power pad.

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