LTC4366 datasheet(17/22 Pages) AD

17 / 22 page

LTC4249

Rev. 0

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When the load is resistive, the calculation for ROV

is unchanged. For VOUT = 48V and IOC = 732mA, ROV

remains 1MΩ. However, the calculation for OV threshold

must include an additional contribution from IMON output

current due to the excess voltage over the resistive load:

VOV =1.2V•

RIMON

ROV

IOUT •GIMON

VOUT

ROV

where IOUT is the nominal load of 650mA yielding a result

of VOV = 51.48V. To regain a higher OV threshold, ROV

must increase, which will cause IOC to increase. For exam-

ple, if ROV is increased to 1.21MΩ, VOV becomes 55.48V

and IOC increases to 813mA.

Reverse Current Circuit Breaker

In applications where the ECB output (load side) could be

pulled above the input, such as a power mux circuit, the

risk of forward biasing the ECB body diode and conduct-

ing current to the input exists. To overcome that possibil-

ity, the two LTC4249 channels can be connected back to

back as shown in Figure 19. The back to back connection

places the two ECB body diodes in opposite directions and

prevents current from the load connection at IN2 back to

IN1, when the ECBs are off.

When the channels are turned on, however, current can

still pass through the ECBs in both directions. Fortunately,

due to the reverse connection of channel 2, current from

IN2 to OUT2 is still reported at IMON2 because channel 2

is operating normally if IN2 rises above OUT2. With an

appropriate choice of RIMON2, an accurate “reverse cur-

rent” threshold can be chosen to shut off channel 2 and

prevent excess current from the load connection at IN2

back to IN1. Channel 1 operates as usual and turns off

due to excess forward current, configured by RIMON1.

TO LOAD

6V TO 65V

RIMON1

10F

CLOAD

GND

IN1

OUT1

EN1

RDY1

LTC4249

IMON1

IMON2

RDY2

IN2

EN2

OUT2

INTVCC

0.1F

SOME CONNECTIONS

OMITTED FOR CLARITY

ENABLE

RIMON2

4249 F19

Figure 19. Back to Back Connection for Load Isolation

and Forward/Reverse Current Circuit Breaker

Load Switch with Isolation

Building from Figure 19, a load switch with reverse isola-

tion is possible by duplicating the application and provid-

ing enable inputs to preferentially select the input supply

(V1 or V2) that is delivered to the load (Figure 20).

APPLICATIONS INFORMATION

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