LT4363 datasheet(16/22 Pages) AD

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LTC4249

Rev. 0

For more information www.analog.com

The recommended bias sequence during power down is

the following:

1) Remove RFIN signal.

2) Decrease PA VGG voltage to bring PA BIAS current to

zero. BIAS current may be inferred from the voltage at

the IMON output.

3) Pull EN below threshold (OUT disconnects from IN,

RDY pulls low).

Current Sharing

Some applications may require operation and OC sensing

above 1.2A load current. Operation up to 2.4A is possible

by simply paralleling the two ECB channels (Figure 17).

The two channels will share load current to typically 1%,

governed by RON matching.

If either channel exceeds 1.2A, the respective ECB shuts

off. This action throws the load current to the remaining

channel causing the second channel to shut off as well.

Multiple LTC4249s may be paralleled for even more cur-

rent. The efficacy of that approach depends on device to

device RON matching (typically ±2%, but is not guaran-

teed), and is slightly worse than the ±1% channel match-

ing specification.

TO LOAD

6V TO 65V

RIMON

22F

GND

IN1

OUT1

EN1

RDY1

LTC4249

IMON1

IMON2

RDY2

IN2

EN2

OUT2

INTVCC

0.1F

SOME CONNECTIONS

OMITTED FOR CLARITY

ENABLE

RIMON

4249 F17

Figure 17. Current Sharing for Applications above 1.2A

Output Overcurrent and Overvoltage

Circuit breaker action may also be achieved based on over-

voltage at the OUT node by the addition of a single resis-

tor ROV (Figure 18) between OUT and IMON. Calculating

resistor ROV depends on whether the load has current sink

or resistive properties. In this application, the OC and OV

thresholds become dependent and resistor calculation is

a multi-step procedure.

ROV

48V

RIMON

GND

IN1

OUT1

EN1

RDY1

LTC4249

IMON1

IMON2

RDY2

IN2

EN2

OUT2

INTVCC

0.1F

SOME CONNECTIONS

OMITTED FOR CLARITY

ENABLE

CURRENT SINK

OR RESISTOR LOAD

LOAD ENABLE

4249 F18

Figure 18. OV/OC Circuit Breaker with One Additional Resistor

The nominal OUT1 voltage (VOUT) in Figure 18 is ~48V

with a desired OV threshold (VOV)of 56.2V. For a cur-

rent sink load (IOUT) operating nominally at 650mA and

a desired overcurrent threshold (IOC) of 732mA, ROV is

found from:

ROV =

VOUT 1.2V

1.2V

RIMON

IOC•GIMON

(

)

where GIMON = 100µA/A and RIMON = 10kΩ. Plugging in

IOC = 732mA yields ROV = 1MΩ. With ROV at 1MΩ and

IOUT = 650mA, VOV is determined from:

VOV =

1.2V

RIMON

IOUT •GIMON

(

) •ROV +1.2V

with a result of VOV = 56.2V.

APPLICATIONS INFORMATION

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