A8450KLBTR-T【PDF 8/17 页】IC REG QD BUCK/LINEAR 24-SOIC

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Automotive Multioutput Voltage Regulator

A8450

Allegro MicroSystems, LLC

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

Functional Description

Buck Converter with Switching Regulator. A current-

mode, variable frequency buck DC-to-DC converter and switch-

ing regulator are integrated in the A8450, as shown in figure 2.

This feature allows the device to efficiently handle power over a

wide range of input supply levels. The DC-to-DC converter out-

puts 5.7 V typical, and has an overcurrent limit of 1.2 A typical.

The converter employs a soft-start feature. This ramps the con-

verter output voltage and limits the maximum demand on V

REG

by controlling the inrush current required at power-on to charge

the external capacitor, COUT, and any DC load.

An internal charge pump provides gate drive for the

N-channel MOSFET buck switch. A 100% duty cycle is imple-

mented when using low V

input voltages.

At V

lower than 12 V, off-time, t

OFF

, is reduced, as shown in

figure 3. This reduction keeps the switching frequency, f

PWM

within a reasonable range and lowers the ripple current. Lowering

the ripple current at low V

levels prevents degradation of linear

regulator headroom due to V

REG

ripple voltage.

5 V Linear Regulators. Two 5 V medium-power linear regulators

are provided. These low-dropout regulators feature foldback current

limiting for short-to-ground protection. When a direct short is applied

to the regulator output, either V5A or V5D, the current folds back

Figure 2. Buck converter with switching regulator

Figure 3. When VBB falls below 12 V, t

OFF

decreases

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

OFF

by V

(V)

4.75 約

12 V

2.05 約

11 V

0.58 約

6.02 V

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