A4402KLPTR-T データシートの表示（PDF） - Allegro MicroSystems

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A4402KLPTR-T

Constant On-Time Buck Converter With Integrated Linear Regulator

Allegro MicroSystems 

A4402

Constant On-Time Buck Converter

With Integrated Linear Regulator

where:

IOUT(av) is the average of both output currents,

IRIPPLE is the inductor ripple current, and

K is a guardband margin. The peak current in the switch is then:

IPEAK = IVALLEY + IRIPPLE .

(8)

The valley current must be calculated so that, at the worst-case

ripple, the converter can still supply the required current to the

load. Further information on how to calculate the ripple current is

included in the Application Information section.

ENB An active high input enables the device. When set low, the

device enters sleep mode; all internal circuitry is disabled, and the

part draws a maximum of 1 μA.

Thermal Shutdown When the device junction temperature, TJ ,

is sensed to be at TJTSD, a thermal shutdown circuit disables the

regulator output, protecting the A4402 from damage.

Power-on Reset Delay The POR function monitors the VFB2

voltage and provides a signal that can be used to reset a DSP or

microcontroller. A POR event is triggered by either of the

following conditions:

• VFB2 falls below its UVLO threshold. This occurs if the current

limit on either regulator is exceeded, or if the switcher voltage

falls due to TSD.

• After a rising edge on the WDI input, the voltage on TSET

reaches VTRIP.

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

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

occurs after an adjustable delay, tPOR, set by an external capacitor

connected to the POR pin. The value of tPOR is calculated using

the following formula:

tPOR = 214 × 103 × CPOR ,

(9)

where CPOR is the value of the POR capacitor in farads, and tPOR

is the POR time in seconds.

Shutdown The buck regulator will shutdown if one of the fol-

lowing conditions is present:

• TSD

• ENB falling edge

Allegro MicroSystems, Inc.

10

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

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