9

A8450KLB-DS, Rev. 1

Worcester, Massachusetts 01615-0036 (508) 853-5000

115 Northeast Cutoff, Box 15036

www.allegromicro.com

Allegro MicroSystems, Inc.

A8450

Automotive Multioutput Voltage Regulator

ENBAT is an edge-triggered enable (logic 1 ≥ 2.7 V), which

is used to enable the A8450 in response to a high-voltage

signal, such as from an automobile ignition or battery switch.

In this capacity, ENBAT is used only as a momentary switch

to wake up the device. If there is no need for a high-voltage

signal, ENBAT can be pulled low continuously.

ENB is used to initiate the reset of the device. If ENBAT is

pulled low, ENB acts as a single reset control.

Diagnostics. An open drain output, through the NFAULT

pin, is pulled low to signal to a DSP or microcontroller any of

the following fault conditions:

• V5A, the 5 V analog regulator output, is shorted to supply

• Either or both of the V5A and the V5D regulator outputs

Charge Pump. The charge pump generates a voltage above

buck switch.A0.1 µF ceramic monolithic capacitor, C7, should

be connected between the VCP pin and the VBB pin, to act as

a reservoir to run the buck converter switching regulator.

disabled in the case of a fault condition. In addition, a 0.1 µF

ceramic monolithic capacitor, C8, should be connected between

CP1 and CP2.

Power On Reset Delay. The POR block monitors the sup-

ply voltages and provides a signal that can be used to reset a

DSP or microcontroller. A POR event is triggered by any of

the following conditions:

• Either V33 or VADJ is pulled below its UVLO threshold,

• Both input signal pins, ENB and ENBAT, are pulled low.

This immediately pulls the NPOR pin low, indicating that

the device is beginning a power-off sequence. In addition,

the buck converter switching regulator is disabled, and

the VREG supply begins to ramp down. The rate at which

and value of the output capacitors (C1, C2, C3, and C4).

An open drain output, through the NPOR pin, is provided to

signal a POR event to the DSP or microcontroller. The reset

calculated using the following formula

A POR can be forced without a significant drop in the supply

pins. However, pulse duration should be short enough so that

Thermal Shutdown. When the device junction temperature,

pin. At the same time, a thermal shutdown circuit disables the

buck converter, protecting the A8450 from damage.