Three new automotive power management ICs use an internal 2.2-MHz constant on-time buck pre-regulator to supply regulated outputs commonly used in automotive CAN and microprocessor controlled applications. These new devices target 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 5VP 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 VP 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 VIN 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 EMI in the AM frequency band.
Protection features include under-voltage lockout, pulse-by-pulse current limit, LX short circuit protection, and thermal shutdown. In case of a shorted load, all linear regulators feature fold back over-current protection and the V5P 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 (NPOR) output with adjustable delay for microprocessor control.
Allegro MicroSystems Inc., 115 Northeast Cutoff, Worcester, MA 01606. Phone: (508) 853-5000.
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