LT3045 datasheet(21/32 Pages) LINER

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LT3045

3045fa

For more information www.linear.com/LT3045

applicaTions inForMaTion

If OUTS is externally held above SET, the current sink

turns ON in an attempt to restore OUTS to its programmed

voltage. The current sink remains ON until the external

circuitry releases OUTS.

Direct Paralleling for Higher Current

Higher output current is obtained by paralleling multiple

LT3045s. Tie all SET pins together and all IN pins together.

Connect the OUT pins together using small pieces of PCB

trace (used as a ballast resistor) to equalize currents in

the LT3045s. PCB trace resistance in milliohms/inch is

shown in Table 2.

Table 2. PC Board Trace Resistance

WEIGHT (oz)

10mil WIDTH

20mil WIDTH

54.3

27.1

13.6

Trace resistance is measured in mΩ/in.

The small worst-case offset of 2mV for each paralleled

LT3045 minimizes the required ballast resistor value.

Figure 7 illustrates that two LT3045s, each using a 20mΩ

PCBtraceballastresistor,providebetterthan20%accurate

output current sharing at full load. The two 20mΩ external

resistors only add 10mV of output regulation drop with a

1A maximum current. With a 3.3V output, this only adds

0.3% to the regulation accuracy. As has been discussed

previously,tietheOUTSpindirectlytotheoutputcapacitor.

More than two LT3045s can also be paralleled for even

higher output current and lower output noise. Paralleling

multiple LT3045s is also useful for distributing heat on the

PCB. For applications with high input-to-output voltage

differential, an input series resistor or resistor in parallel

with the LT3045 can also be used to spread heat.

PCB Layout Considerations

Given the LT3045’s high bandwidth and ultrahigh PSRR,

carefulPCBlayoutmustbeemployedtoachievefulldevice

performance. Figure 8 shows a recommended layout that

delivers full performance of the regulator. Refer to the

LT3045’sDC2491Ademoboardmanualforfurtherdetails.

Figure 8. Recommended DFN Layout

100µA

EN/UV

PGFB

GND

OUT

LT3045

ILIM

10µF

20m

VOUT

3.3V

IOUT(MAX)

3045 F07

16.5k

SET

OUTS

100µA

EN/UV

PGFB

GND

OUT

LT3045

ILIM

10µF

20m

10µF

VIN

5V ±5%

SET

OUTS

0.47µF

Figure 7. Parallel Devices

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