LTC4413 datasheet(13/32 Pages) AD

13 / 32 page

LTC4421

Rev. 0

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Introduction

High availability systems employ multiple input supplies

to power a single common output. When individual sup-

plies such as wall adapters and batteries are unplugged at

various points in time, output power must not brown out

as control of the output power is transferred to the other

supply. Power ORing diodes are often used in these sys-

tems, but the highest input supply voltage always pow-

ers the output. The LTC4421 powers the output from

the highest priority supply available, even if it is lower

in voltage than the lower priority supplies. When switch-

ing between supplies, output voltage droop is minimized,

and backfeeding current is prevented. A typical LTC4421

application circuit is shown in Figure 1, where the primary

APPLICATIONS INFORMATION

input supply is 12V and the secondary is 28V. External

component selection is discussed in detail in the follow-

ing sections.

Setting Valid Operating Voltage Range

The LTC4421 requires an input supply remain inside a

user-defined voltage window for a user-defined amount of

time to be considered valid. The valid voltage window is

set by a resistive divider from the input supply to ground

that allows three thresholds voltages to be configured:

the UV rising threshold (VUVRISE), the UV falling thresh-

old (VUVFALL) and the OV rising threshold (VOVRISE). The

OV falling threshold is set by internal hysteresis to be

10% below the OV rising threshold. Using the 500mV

Figure 1. Typical LTC4421 Application Circuit

LTC4421 F01

CINTVCC

1µF

35.7k

12.7k

20k

15.4k

6.19k

69.8k

0.1µF

PSMN4R8100BSE

PSMN1R440YLD

PSMN4R8100BSE

PSMN1R440YLD

CCP0

1µF

CTMR2

47nF

CTMR1

47nF

CQUAL

470pF

COUT

220µF

SMDJ36A

RSENSE1

2.5m

RSENSE2

GATE1 SOURCE1

OUT2

GATE2 SOURCE2

EXTVCC

INTVCC

TMR1

OV1

OV2

CPO

SENSE1

SENSE2

VALID1

VALID2

GND

FAULT1

FAULT2

CH1

CH2

DISABLE1

DISABLE2

SHDN

UVF1

UVF2

UVR1

UVR2

OUT1

TMR2

CASIN

CASOUT

QUAL

RETRY

CPOREF

CG2

47nF

CG1

47nF

PRIMARY

12V

VOUT

SECONDARY

28V

LTC4421

DIGITAL

STATUS

OUTPUTS

DIGITAL

CONTROL

INPUTS

UVF1 = 7.81V

UVR1 = 11.04V

OV1 = 14.96V

UVF2 = 5.97V

UVR2 = 25.28V

OV2 = 35.4V

RSN1

1.2

CSN1

10µF

RSN2

2.8

CSN2

10µF

ILIM1 = 10A

ILIM2 = 10A

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