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dc2438af

DEMO MANUAL DC2438A

Description

LTM2894

7.5kVRMS Isolated USB

Data Transceiver

Demonstration circuit 2438A is an isolated USB data

transceiver featuring the LT M

2894. The demo circuit

features an EMI optimized circuit configuration, including

an isolated DC-DC converter, and printed circuit board

layout. All components for data signaling and isolation

are integrated into the LTM2894 using LTC’s isolator

µModule

technology. The demo circuit operates from a L, LT, LTC, LTM, Linear Technology, µModule and the Linear logo are registered trademarks of

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

performance summary

operating principles

supply on VCC and/or VBUS. The DC-DC converter gener-

ates an unregulated isolated output voltage on VCC2 and

regulated 5V for USB communication on VBUS2.

Design files for this circuit board are available at

http://www.linear.com/demo/DC2438A

Specifications are at TA = 25°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VCC Operating Supply Range (Isolated Power Input) 4.4 6 45 V

VBUS Operating Supply Range (USB Bus Power

Input)

4.4 5 5.5 V

VCC2 Input Operating Range (DC-DC Off)

VCC Input Operating Range (DC-DC On)

Output Voltage

VBUS = 4.4V, ICC2 = 200mA

VCC = 6V, ICC2 = 500mA

4.4

5.5

7.5

tLDR Low Speed Data Rate 1.5 Mbps

tFDR Full Speed Data Rate 12 Mbps

VIORM Maximum Working Insulation Voltage GND to GND2 1414

1000

VDC

VRMS

Common Mode Transient Immunity 50 kV/µs

The LTM2894 demo board includes an isolated DC-DC

converter delivering power to VCC2 at approximately

6V from the input supply VCC and/or VBUS. Isolation is

maintained by the separation of GND and GND2 where

significant operating voltages and transients can exist

without affecting the operation of the LTM2894. The logic

side is enabled upon connection of a USB cable via the

LTM2894 ON pin. All logic side signals are referenced to

the logic supply pin VLO. The LTM2894 has two power

supply inputs, VCC and VBUS. For applications requiring

more than 200mA from VCC2, VCC must be connected to

an external supply of 6V to 7V. VBUS may be connected

to USB bus power to enable data communication. If the

isolated DC-DC converter is not needed then VCC2 may

be driven by an external voltage.

Upstream USB signaling is controlled by the bidirectional

pins D1+ and D1–. A 1.5k pull-up resistor is automatically

configured dependent upon the connected downstream

peripheral device. For full speed operation a 1.5k pull-up is

asserted on D1+, for low speed mode on D1–. The down-

stream USB data pins, D2+ and D2–, each have integrated

15k pull-down resistors.

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DEMO MANUAL DC2438A

operating principles

Quick start proceDure

Figure 1. DC2438A Radiated Emissions

Figure 2. Demo Board Setup

The demo circuit has been designed and optimized for

low RF emissions. EMI mitigation techniques used include

the following:

1. Board/ground plane size has been minimized. This

reduces the dipole antenna formed between the logic

side and isolated side ground planes.

2. Top signal routing and ground floods have been opti-

mized to reduce signal loops, minimizing differential

mode radiation.

3. The DC-DC converter uses a cascaded transformer

arrangement, where the first transformer’s isolated

side center tap is connected to logic side ground. This

effectively returns all common mode currents generated

by the switching converter edge rate and transformer

parasitic capacitance.

EMI performance is shown in Figure 1, measured using

a gigahertz transverse electromagnetic (GTEM) cell and

method detailed in IEC 61000-4-20, “Testing and Mea-

surement Techniques – Emission and Immunity Testing

in T

ransverse Electromagnetic Waveguides”.

Demonstration circuit 2438A is easy to set up and evalu-

ate the performance of the LTM2894. Refer to Figure 2

for proper measurement equipment setup and follow the

procedure below.

NOTE: When measuring the input or output voltage ripple

or high speed signals, care must be taken to avoid a long

ground lead on the oscilloscope probe.

1. Connect external power supply to VCC and GND if greater

than 200mA is required from VCC2 or VBUS2.

2. Connect USB cable from computer to input side (J1) of

the demo board.

3. Connect computer mouse, low speed device, or USB

memory stick, typically high speed device, to output

side (J2) of demo board.

4. Verify proper operation of mouse or memory stick.

CISPR 22 CLASS B LIMIT

DETECTOR = PEAK–HOLD

RBW = 120kHz, VBW = 300kHz

SWEEP TIME = 680ms

# OF SWEEPS ≥10

# OF POINTS = 501

DC2438A

FREQUENCY (MHz)

100

200

300

400

500

600

700

800

900

1000

–30

–20

–10

AMPLITUDE (dBµV/m)

DC2438a F01

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DEMO MANUAL DC2438A

Quick start proceDure

Figure 3. Layer 1 Top Layer

Figure 4. Layer 2 Bottom Layer

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DEMO MANUAL DC2438A

parts list

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 1 U1 IC, LTM2894IY LINEAR LTM2894IY#PBF

Hardware: For Demo Board Only

2 1 C1 Cap, Tantalum 4.7μF 10% 2312 50V AVX TAJC475K050RNJ

3 1 C2 Cap, Ceramic 180pF 5% 0603 100V C0G AVX 06031A181JAT2A

4 2 C3, C6 Cap, Ceramic 4.7µF 10% 1210 50V X7R AVX 12105C475KAT2A

5 2 C4, C5 Cap, Ceramic 47pF 5% 0603 100V C0G AVX 06031A470JAT2A

6 1 C7 Cap, Ceramic 22nF 10% 0603 25V X7R AVX 06033C223KAT2A

7 1 C8 Cap, Ceramic 1nF 10% 0603 50V X7R AVX 06035C102KAT2A

8 1 C9 Cap, Ceramic 10nF 10% 0603 50V X7R AVX 06035C103KAT2A

9 1 C10 Cap, Ceramic 10µF 10% 0805 10V X7R Murata GRM21BR71A106KE51L

10 4 D1 to D4 Diode, Schottky, 80V 500mA SOD123 Diodes Inc. MBR0580S1-7

11 1 J1 USB RECEPTACLE TYPE B Wurth Elektronik 61400416121

12 1 J2 USB RECEPTACLE TYPE A Wurth Elektronik 61400416021

13 4 JP1 to JP4 Header, Loop 1x2 0.2˝ Aavid 125700D00000G

14 1 L1 Inducotr, 10µH 1008 0.5Ω 0.25A Wurth Elektronik 74479888310

15 3 R1, R6, R7 Resistor, 100kΩ 1% 0603 Vishay CRCW0603100KFKEA

16 1 R2 Resistor, 464kΩ 1% 0603 Vishay CRCW0603464KFKEA

17 1 R3 Resistor, 28kΩ 1% 0603 Vishay CRCW060328K0FKEA

18 1 R4 Resistor, 49.9kΩ 1% 0603 Vishay CRCW060349K9FKEA

19 1 R5 Resistor, 39Ω 1% 0805 Vishay CRCW080539R0FKEA

20 2 R8, R9 Resistor, 249Ω 1% 0805 Vishay CRCW0805249RFKEA

21 1 TR1 Transformer, 2.5kV 1:1.1 Wurth Elektronik 760390012

22 1 TR2 Transformer, 5kV 1:1.7 Wurth Elektronik 750313769

23 1 U2 IC, 1A, 1MHz, Push-Pull DC-DC Driver LINEAR LT3999IMSE#PBF

24 1 U3 IC, 45V VIN, Low Noise, 500mA LDO LINEAR LT3065IDD-5#PBF

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DEMO MANUAL DC2438A

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

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DEMO MANUAL DC2438A

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

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

LT 0316 • 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