Linear Technology DC2491A Guida rapida alla configurazione

dc2491af

DEMO MANUAL DC2491A

DESCRIPTION

LT3045EDD

20V, 500mA, Ultralow Noise

Ultrahigh PSRR RF LDO Regulator

DemocircuitDC2491AfeaturestheLT

3045EDD,a500mA,

ultralow noise and ultrahigh power supply rejection

ratio(PSRR) low dropout (LDO) regulator with program-

mable current limit.

DC2491A operates over an input voltage range of 3.8V

to 20V. The LT3045 delivers a maximum output current

of 500mA. In addition to featuring ultralow noise and

ultrahigh PSRR, the regulator offers programmable power

good functionality as well as programmable current limit.

Current monitoring is also achieved by sensing the ILIM

pin voltage.

Built-in protection includes reverse battery protection,

reverse current protection, internal current limit with

foldback, and thermal limit with hysteresis.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

PERFORMANCE SUMMARY

The LT3045 data sheet gives a complete description of the

device, operation and applications information. The data

sheet must be read in conjunction with this demo manual

for DC2491A. The LT3045EDD is assembled in a 10-lead

(3mm × 3mm) plastic DFN package with an exposed pad

on the bottom-side of the IC. Proper board layout is es-

sential for maximum thermal performance.

Design files for this circuit board are available at

http://www.linear.com/demo/DC2491A

Specifications are at TA= 25°C

PARAMETER CONDITIONS MIN TYP MAX

Input Voltage Range (VIN) IOUT = 150mA, VOUT = 3.3V 3.8V 20V

Input Voltage Range (VIN) IOUT = 500mA, VOUT = 3.3V 3.8V 8.3V*

Output Voltage (VOUT) VIN = 5V, IOUT = 500mA 3.2V 3.3V 3.4V

Shutdown Input Current (IIN) JP1 = OFF, VIN = 5V 0.1μA

*The maximum input voltage for 500mA load current is set by the 60°C temperature rise of LT3045 on the demo circuit. Higher input voltage can be

reached if larger copper area or force-air cooling is applied. The output current is also limited by the differential of input and output voltage, please refer

the data sheet for details.

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DEMO MANUAL DC2491A

QUICK START PROCEDURE

Figure 1. Test Procedure Setup Drawing for DC2491A

DC2491A is easy to set up to evaluate the performance of

the LT3045EDD. Refer to Figure 1 for proper measurement

equipment setup and follow the procedure below.

1. Connect load between VOUT and GND terminals.

2. With power off, connect the input power supply to the

VIN and GND terminals.

3. Make sure the shunt of JP1 is at ON option.

4. Turn the input power supply on and make sure the

voltage is between 3.8V and 20V.

5. Refer to Application Notes AN70 and AN159 for mea-

suring output noise and PSRR.

6. With JP1 at USER SELECT option, R6 and R7 can be

used to set an accurate undervoltage lockout (UVLO)

threshold.

*The maximum output current will be limited by internal current limit based on differential voltage of input and output voltage, please refer to the data sheet.

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DEMO MANUAL DC2491A

Figure 2. Layer 3 of DC2491A

Best PSRR Performance: PCB Layout for Input Trace

For applications utilizing the LT3045 for post-regulating

switching converters, placing a capacitor directly at the

LT3045 input results in AC current (at the switching fre-

quency) to flow near the LT3045. Without careful attention

to PCB layout, this relatively high frequency switching cur-

rent generates an electromagnetic field (EMF) that couples

totheLT3045 output, thereby degrading its effectivePSRR.

While highly dependent on the PCB, the switching pre-

regulator, and the input capacitor size, amongother factors,

the PSRR degradation can easily be 30dB at 1MHz. This

degradation is present even if the LT3045 is de-soldered

from the board, because it effectively degrades the PSRR

of the PC board itself. While negligible for conventional low

PSRR LDOs, LT3045’s ultrahigh PSRR requires careful

attention to higher order parasitics in order to realize the

full performance offered by the regulator.

PCB LAYOUT

The LT3045 demo board alleviates this degradation in

PSRR by using a specialized layout technique. On layer3,

the input trace (VIN) is highlighted in red, with the return

path (GND) highlighted on the bottom layer together with

input capacitor C1. When an AC voltage is applied to the

input of the board, AC current flows on this path, thus

generating EMF. This EMF couples to output capacitor

C2 and related traces, making the PSRR appear worse

than it actually is. With the input trace directly above

the return path, the EMFs are in opposite directions,

and consequently cancel each other out. Making sure

these traces exactly overlap each other maximizes the

cancellation effect and thus provides the maximum

PSRR offered by the regulator.

Figure 3. Bottom Layer of DC2491A

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DEMO MANUAL DC2491A

Figure 5. Split Pads for C2 on Top Layer of DC2491A

Best AC Performance: PCB Layout for Output

Capacitor C2

For ultrahigh PSRR performance, the LT3045 bandwidth

is made quite high (~1MHz), making it very close to the

output capacitor’s self-resonance frequency (~1.6MHz).

Therefore, it is very important to avoid adding extra imped-

ance (ESL and ESR) outside the feedback loop. To that end,

minimize the effects of PCB trace and solder inductance

by Kelvin connecting OUTS and SET pin capacitor (CSET)

GND directly to output capacitor (C2) terminals using split

capacitor techniques. Pad 4 connects to the OUTS pin and

Pad 1 connects to the GND side of the SET pin capacitor.

With only small AC current flowing through these connec-

tions, the impact of solder joint/PCB trace inductance on

stability is eliminated. While the LT3045 is robust enough

not to oscillate if the recommended layout is not followed,

phase/gain margin and PSRR will degrade.

SET

OUT

SET

LT3045

100μA

OUTS

ILIM

GND

PGFB

EN/UV

OUT

PCB LAYOUT

Figure 4. C2 and CSET Connections for Best Performance

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DEMO MANUAL DC2491A

BOARD PHOTO

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DEMO MANUAL DC2491A

PARTS LIST

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 1 CIN CAP., ALUM, 22µF, 35V, 5mm × 5.4mm SUN ELECTRONIC INDUSTRIES CORP., 35CE22BSS

2 2 C1, C4 CAP., X7R, 4.7μF, 25V, 10% 1206 MURATA, GRM31CR71E475KA88L

3 1 C2 CAP., X5R, 10μF, 25V, 10% 1206 MURATA, GJ831CR61E106KE83L

4 1 R1 RES., CHIP, 200k, 1/16W, 5% 0603 VISHAY, CRCW0603200KJNED

5 1 R3 RES., CHIP, 33.2k, 1/8W, 1% 0603 VISHAY, CRCW060333K2FKEA

6 1 R5 RES., CHIP, 453k, 1/8W, 1% 0603 VISHAY, CRCW0603453KFKEA

7 1 R6 RES., CHIP, 49.9k, 1/8W, 1% 0603 VISHAY, CRCW060349K9FKEA

8 1 R7 RES., CHIP, 249Ω, 1/16W, 1% 0603 VISHAY, CRCW0603249RFKEA

9 1 U1 IC, LT3045EDD DFN 3mm × 3mm LINEAR TECH., LT3045EDD#PBF

Optional Electronic Components

1 0 C3, C5 (OPT) CAP., 1206

2 0 R2, R4 (OPT) RES., 0603

31 R8 RES., CHIP, 0Ω, 1/16W, 5% 0603 VISHAY, CRCW06030000Z0EA

Hardware

1 6 E1 – E6 TESTPOINT, TURRET, 0.094" PBF MILL-MAX, 2501-2-00-80-00-00-07-0

2 1 JP1 HEADER 3-PIN 0.079" DOUBLE ROW WURTH ELEKTRONIK, 62000621121

3 1 XJP1 SHUNT, 0.079" CENTER WURTH ELEKTRONIK, 60800213421

4 2 J1, J2 CONN, BNC, 5 PINS CONNEX, 112404

5 4 MH1 – MH4 STAND-OFF, NYLON 6.4mm WURTH ELEKTRONIK, 702931000

dc2491af

DEMO MANUAL DC2491A

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

SCHEMATIC DIAGRAM

1. ALL RESISTORS ARE 0603.

NOTE: UNLESS OTHERWISE SPECIFIED

SEE DEMO MANUAL

LT3045EDD

EN/UV

ILIM

OUT 10

OUTS 9

GND

SET 7

PGFB 6

GND

OPT

1206

MONITOR

OUTPUT NOISE

249

OPT

GND

453K

JP1

USER SELECT

OFF

EN/UV

1 2

5 6

4.7uF

1206

25V

200K

CIN

22µF

35V

35CE22BSS

10uF

25V

1206

OPT

1206

GND

MONITOR

INPUT RIPPLE

VIN

3.8V-20V

OPT

33.2K

49.9K

EN/UV

E5 3.3V, 500mA

VOUT

4.7uF

1206

25V

dc2491af

DEMO MANUAL DC2491A

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ●FAX: (408) 434-0507 ●www.linear.com

LT 0816 • PRINTED IN USA

DEMONSTRATION BOARD IMPORTANT NOTICE

Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:

This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT

OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete

in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety

measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union

directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.

If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date

of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU

OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS

FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR

ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.

The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims

arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all

appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or

agency certified (FCC, UL, CE, etc.).

No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,

customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.

LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.

Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and

observe good laboratory practice standards. Common sense is encouraged.

This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application

engineer.

Mailing Address:

Linear Technology

1630 McCarthy Blvd.

Milpitas, CA 95035

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