LT3045 datasheet(22/36 Pages) LINER

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LT3045-1

30451fa

For more information www.linear.com/LT3045-1

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

LT3045-1s.TieallSETpinstogetherandallINpinstogether.

Connect the OUT pins together using small pieces of PCB

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

the LT3045-1s. 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

LT3045-1 minimizes the required ballast resistor value.

Figure 7illustratesthattwoLT3045-1s,eachusinga20mΩ

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 LT3045-1s can also be paralleled for even

higher output current and lower output noise. Paralleling

multiple LT3045-1s is also useful for distributing heat on

thePCB.Forapplicationswithhighinput-to-outputvoltage

differential, an input series resistor or resistor in parallel

with the LT3045-1 can also be used to spread heat.

PCB Layout Considerations

Given the LT3045-1’s high bandwidth and ultrahigh

PSRR, careful PCB layout must be employed to achieve

full device performance. Figure 8 shows a recommended

layout that delivers full performance of the regulator.

Refer to the LT3045-1’s DC2593A demo board manual

for further details.

Figure 7. Parallel Devices

Figure 8. Recommended DFN Layout

100µA

EN/UV

PGFB

GND

OUT

LT3045-1

ILIM

10µF

20m

VOUT

3.3V

IOUT(MAX)

30451 F07

16.5k

SET

OUTS

100µA

EN/UV

PGFB

GND

OUT

LT3045-1

VIOC

ILIM

10µF

20m

10µF

VIN

5V ±5%

SET

OUTS

0.47µF

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