Automotive multiple-output regulator ICs feature 2.2 MHz switching

October 16, 2012 // By Christoph Hammerschmidt
Three new automotive power management ICs from Allegro MicroSystems Europe use an internal 2.2 MHz constant on-time buck pre-regulator to supply regulated outputs commonly used in automotive CAN Bus and microprocessor-controlled applications.

These new devices are targeted at the automotive market for bias supplies within control units for functions such as electronic power steering, transmission control, antilock braking and emissions control.

The A4407 supports four regulated outputs: a 5 V linear regulator, a 5 V tracking/protected linear regulator, a 3.3 V linear FET controller/driver and an adjustable linear regulated output. The A4405 supports three regulated outputs: a 5 V linear regulator, a 5 V tracking/protected linear regulator, and a 3.3 V linear FET controller/driver. The A4406 is a scaled-down version of the A4405 and can supply a 5 V tracking/protected linear regulator and a 3.3 V linear FET controller/driver.

The 5 V protected output of the A4405 and A4406 tracks the 3.3 V output, while the A4407 provides a pin to set the master reference for the 5 V protected tracking regulator to either the 3.3 V or the second 5 V output. The on-time of the buck pre-regulator is internally adjusted as a function of the input voltage to maintain the 2.2 MHz switching frequency.

Efficient operation is achieved by using the buck pre-regulator to drop the input voltage before supplying the linear regulators.

The buck switching pre-regulator is designed to operate at a nominal switching frequency of 2.2 MHz. The high switching frequency enables the customer to select low value inductors and ceramic capacitors while avoiding electromagnetic interference in the AM frequency band.

Protection features include undervoltage lockout, pulse-by-pulse current limit, LX short-circuit protection, and thermal shutdown. In case of a shorted load, all linear regulators feature foldback overcurrent protection and the protected 5 V output is protected from a short-to-battery event.

All three devices feature both a logic level and a high-voltage (current and voltage limited) enable input. They also integrate a power-on reset output with adjustable delay for microprocessor control.

The A4405 and A4406 devices are offered in a 20-pin TSSOP package and the 407 is offered in