A4405: Constant On-Time Buck Regulator with One External and Two Internal Linear Regulators


The A4405 is an automotive power management IC that uses a high frequency constant on-time 5.45 V pre-regulator to supply two internal 5 V linear regulators and a 3.3 V linear DMOS driver. Designed to supply CAN and microprocessor power supplies in high temperature environments, the A4405 is ideal for under hood applications. Efficient operation is achieved by using a buck pre-regulator to efficiently drop the input voltage before supplying the linear regulators; this reduces power dissipation and increases overall regulator efficiency.

The switching regulator is capable of operating 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 undervoltage lockout and thermal shutdown. The V5P output is protected from short-to-battery events. In case of a shorted load, all regulators feature overcurrent protection.

The A4405 also features power-on-reset with adjustable delay for the microprocessor output. The A4405 is supplied in a low profile (1.2 mm max) 20-pin TSSOP package with exposed thermal pad (suffix LP). The package is lead (Pb) free with 100% matte-tin leadframe plating.

Top Features

  • AEC-Q100 Grade 0 qualified
  • Internal buck pre-regulator followed by LDO outputs
  • 5.5 to 36 V VIN operating range (50 V maximum); for start/stop, cold crank, and load dump requirements
  • 2.2 MHz constant on-time buck regulator
  • Valley current sensing achieves shortest buck on-times
  • 50 V absolute maximum input voltage for surges
  • 5.5 to 46 V input voltage range
  • 40ºC to 150ºC junction temperature range
  • Power-on reset (NPOR pin) with adjustable rising delay
  • 5 V (V5P pin) internal low dropout tracking linear regulator with both overcurrent foldback and short-to-battery protection
  • 5 V (V5 pin) internal low dropout linear regulator with overcurrent foldback protection
  • 3.3 V (V33 pin) external linear regulator DMOS driver with a programmable current limit (up to 500 mA) and overcurrent foldback protection
  • Logic enable input (ENB pin)
  • Ignition enable input (ENBAT pin)
  • Ignition status indicator (ENBATS pin)
  • Buck pulse-by-pulse overcurrent protection
  • Buck LX short circuit protection (latched)
  • Missing asynchronous diode protection (latched)
  • Switcher (VREG pin), 3.3 V (V33 pin), and charge pump
  • (VCP pin) undervoltage lockout protection (UVLO)
  • Thermal shutdown protection (TSD)

Part Number Specifications and Availability

Part Number Package Type Temperature RoHS
Part Composition /
RoHS Data
Comments Samples Check Stock
APEK4405KLP-01-MH DEMO BOARD -20°C to 85°C No -- Contact your
local sales rep
Distributor Stock
A4405KLPTR-T 20-lead TSSOP -40°C to 125°C Yes View Data Contact your
local sales rep
Distributor Stock

Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of Allegro’s product can reasonably be expected to cause bodily harm.



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