LINEAR TECHNOLOGY LTC3838EUHF-1 High Current Dual Output Synchronous Buck Converter Owner’s Manual

DEMO MANUAL
DC1997A-A/DC1997A-B
LTC3838EUHF-1/LTC3838EUHF-2
High Current, Dual Output
Synchronous Buck Converter

DESCRIPTION

Demonstration circuits DC1997A-A/DC1997A-B are dual output synchronous buck converters featuring the LT C ® 3838EUHF-1/LTC3838EUHF-2. Both assemblies provide two outputs of 1.5V/20A and 1.2V/20A over an input voltage range of 4.5V to 14V at a switching frequency of 300kHz.
Applications requiring the output to be adjusted with an external reference can be implemented with the DC1997A-B assembly. Such applications include adaptive voltage scaling optimization (AVSO) where the processor voltage is adjusted to achieve optimal efficiency, wide output voltage applications controlled by a DAC, or margining. The 2nd channel of the DC1997A-B assembly is regulated to an onboard 1.2V reference in the default setup. The same reference can be set from 0.8V to 1.5V with a potentiometer or the 2nd channel can regulate to a source external to the board. The 1st channel on the DC1997A-B assembly and both channels on the DC1997A-A version are regulated to the internal reference.

The entire converter, excluding the bulk input and output capacitors, fits within a 1.5in2 area on the board. The high density is a result of the compact, 2-sided drop-in layout and the use of dual channel FETs.
Additional features of this demo board include:

• Remote sensing for each output.
• PLLIN and CLKOUT pins.
• PGOOD, RUN and TRK/SS pins for each output.
• Optional resistors to tie the two outputs together.
• Optional footprint for discrete single channel FETs for higher output current.
• Optional footprints to implement DTR (detect transient) to reduce overshoot following a load release.

Design files for this circuit board are available at http://www.linear.com/demo
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

Specifications are at TA = 25°C, No Airflow

QUICK START PROCEDURE
Demonstration circuit DC1997A-A/DC1997A-B is easy to set up to evaluate the performance of the LTC3838EUHF-1/LTC3838EUHF-2. Please refer to Figure 1 for proper measurement equipment setup and follow the procedure below.

1. With power off, connect the input supply, load and meters as shown in Figure 1. Preset the load to 0A and VIN supply to be 0V. For both assemblies, place the jumpers in the following positions:
   JP4| RUN1| ON
   ---|---|---
   JP1| RUN2| ON
   JP2| MODE| FCM

The DC1997A-B assembly has additional jumpers for the reference circuit. Place these jumpers in the following positions:

2. 2. Adjust the input voltage to be between 4.5V and 14V.
   VOUT1 should be 1.5V ± 2%.
   VOUT2 should be 1.2V ± 2%.

3. Next, apply 20A load to each output and re-measure VOUT.

4. Once the DC regulation is confirmed, observe the output voltage ripple, load step response, efficiency and other parameters.
   Note 1: Use the BNC connectors labeled VOUT1 or VOUT2 to measure the output volt-age ripple.
   Note 2: Do not connect load from the VO1_SNS+ turret to the VO1_SNS- turret or from the VO2_SNS+ turret to the VO2_SNS- turret. This could damage the converter. Only apply load across the stud connectors on the edge of the board.

Reference Circuit for Channel 2 of DC1997A-B Assembly
Channel 2 of the DC1997A-B assembly is configured by default to regulate to the fixed 1.2V reference generated by the LT® 6650 reference circuit. If desired, this reference can be set with a potentiometer, or an external source such as a  DAC or another source. See the following instructions to set the board for either:

Adjusting the Onboard Reference:

1. Remove power from the input of the board.
2. Place these jumpers in the following positions:
   JP5| ON BD REF| ADJ
   ---|---|---
   JP6| REF| ON BD
3. Apply power to the input of the board.
4. Adjust reference with potentiometer at R52.

Connecting a Reference External to the Board:

1. Remove power from the input of the board.
2. Place JP6 in the EXT position.
3. Connect the external reference between the EXTREF2+ and EXTREF2- turrets.
4. Apply power to the input of the board.
5. Turn-on the external reference.
   Note 3: For accurate efficiency measurements in DCM at light load at VIN greater than 5V, remove R51 and apply an external reference to the board as mentioned above.

Single Output/Dual Phase Operation
A single output/dual phase converter may be preferred for higher output current applications. The optional components required to tie the phases together are found on the top middle of the first sheet. To tie the two outputs together, make the following modifications:

1. Tie the two VOUT shapes together with a piece of copper at the edge of the board where the copper is exposed.
2. Tie the VOUT SENSE1+ pin to INTVCC with a 0Ω jumper at R8. This will tie ITH1 to ITH2 inside the chip.
3. Tie RUN1 to RUN2 by stuffing a 0Ω jumper at R15.
4. If DTR is implemented, then stuff 0Ω jumper at R9 to tie the two DTR pins together.

Dynamic Load Circuit (Optional)
Demonstration circuit DC1997A-A/DC1997A-B provides a simple load-step circuit consisting of a MOSFET and sense resistor for each rail. To apply a load step, follow the steps below.

1. Pre-set the amplitude of a pulse generator to 0.0V and the duty cycle to 5% or less.
2. Connect the scope to the VOUT BNC connectors for the rail under test with a coax cable. To monitor the load-step current, connect the scope probe across the ISTEP+/- turrets for that rail.
3. Connect the output of the pulse generator to the PULSE turret for the rail under test and connect the return to the adjacent GND turret.
4. With the converter running, slowly increase the amplitude of the pulse generator output to provide the desired load step pulse height. The scaling for the load step signal is 5mV/Amp.

LTC3838-2 1.5V/20A and 1.2V/20A Converter

Figure 2. Efficiency Curves for the 1.5V Rail and 1.2V Rail of the DC1997A-B Assembly in FCM at VIN = 12V

LTC3838-2 1.5V/20A and 1.2V/20A Converter

Figure 3. Efficiency Curves for the 1.5V Rail and 1.2V Rail of the DC1997A-B Assembly in FCM and DCM at VIN = 12V

VOUT2 of the LTC3838-2 Demo Board Adjusted with External Reference

Figure 4. Efficiency Curves for VOUT2 on the DC1997A-B Assembly at Different Output Voltage Settings

Figure 5. 50% to 100% to 50% Load Step Response of the 1.5V Rail on the DC1997A-A Assembly

Figure 6. 50% to 100% to 50% Load Step Response of the 1.2V Rail on the DC1997A-A Assembly

Figure 7. 50% to 100% to 50% Load Step Response of the 1.5V Rail on the DC1997A-B Assembly

Figure 8. 50% to 100% to 50% Load Step Response of the 1.2V Rail on the DC1997A-B Assembly

Figure 9. Turn-On of the 1.5V Rail of the DC1997A-A Assembly. RUN Pin Released from Ground

Figure 10. Turn-On of the 1.2V Rail of the DC1997A-A Assembly. RUN Pin Released from Ground

Figure 11. Turn-On of the 1.5V Rail of the DC1997A-B Assembly. RUN Pin Released from Ground

Figure 12. Turn-On of the 1.2V Rail of the DC1997A-B Assembly. RUN Pin Released from Ground

PARTS LIST–DC1997A-A

ITEM| QTY| REFERENCE| PART DESCRIPTION| MANUFACTURER/PART NUMBER
---|---|---|---|---

Required Circuit Components

GRM31CR60J107ME39L
13| 4| COUT4, COUT5, COUT9, COUT10| CAP 330µF 2.5V SIZE 7343| SANYO 2R5TPE330M9
14| 2| D1, D2| DIODE SCHOTTKY SOD-323| CENTRAL SEMI. CMDSH-4E TR
15| 2| L1, L2| IND 0.47µH 0.8mΩ DCR| WÜRTH 7443330047
16| 2| Q1, Q2| MOSFET 5mm x 6mm POWER STAGE| INFINEON BSC0911ND
17| 2| R13, R45| RES 100k 1% 0603| VISHAY CRCW0603100KFKEA
18| 6| R2, R11, R19, R44, R4, R12| RES 10k 1% 0603| VISHAY CRCW060310K0FKEA
19| 1| R27| RES CHIP 11k 1% 0603| VISHAY CRCW060311K0FKEA
20| 2| R29, R31| RES 2.2Ω 1% 0603| VISHAY CRCW06032R20FKEA
21| 1| R30| RES 133k 1% 0603| VISHAY CRCW0603133KFKEA
22| 2| R32, R40| RES 15k 1% 0603| VISHAY CRCW060315K0FKEA
23| 12| R5, R17, R21, R23, R25, R35, R38, R41, R42, R50, R14, R24| RES 0Ω,0603| VISHAY CRCW06030000Z0EA
24| 4| R6, R7, R46, R48| RES 10Ω 1% 0603| VISHAY CRCW060310R0FKED
25| 2| RS1, RS2| RES 0.001Ω 1W 1% 2512| VISHAY WSL25121L000FEA
26| 1| U1| LTC3838EUHF-1 QFN 38-LEAD| LINEAR TECH. LTC3838EUHF-1

Additional Circuit Components

Hardware

PARTS LIST–DC1997A-B

Required Circuit Components

GRM31CR60J107ME39L
14| 4| COUT4, COUT5, COUT9, COUT10| CAP 330µF 2.5V SIZE 7343| SANYO 2R5TPE330M9
15| 2| D1, D2| DIODE SCHOTTKY SOD-323| CENTRAL SEMI. CMDSH-4E TR
16| 2| L1, L2| IND 0.47µH 0.8mΩ DCR| WÜRTH 7443330047
17| 2| Q1, Q2| MOSFET 5mm x 6mm POWER STAGE| INFINEON BSC0911ND
18| 3| R13, R24, R45| RES 100k 1% 0603| VISHAY CRCW0603100KFKEA
19| 4| R2, R11, R19, R44| RES 10k 1% 0603| VISHAY CRCW060310K0FKEA
20| 1| R27| RES CHIP 5.23k 1% 0603| VISHAY CRCW06035K23FKEA
21| 2| R29, R31| RES 2.2Ω 1% 0603| VISHAY CRCW06032R20FKEA
22| 1| R30| RES 133k 1% 0603| VISHAY CRCW0603133KFKEA
23| 2| R32, R40| RES 15k 1% 0603| VISHAY CRCW060315K0FKEA
24| 13| R5, R17, R21, R23, R25, R35, R38, R41, R42, R50, R59, R61, R62| RES 0Ω, 0603| VISHAY CRCW06030000Z0EA
25| 4| R6, R7, R46, R48| RES 10Ω 1% 0603| VISHAY CRCW060310R0FKED
26| 2| RS1, RS2| RES 0.001Ω 1W 1% 2512| VISHAY WSL25121L000FEA
27| 1| U1| LTC3838EUHF-2 QFN 38-LEAD| LINEAR TECH. LTC3838EUHF-2

Additional Circuit Components

Hardware

2501-2-00-80-00-00-07-0
3| 6| J1-J6| STUD TEST PIN| PEM KFH-032-10
4| 6| J1-J6| NUT BRASS #10-32| ANY
5| 6| J1-J6| RING LUG #10| KEYSTONE 8205
6| 12| J1-J6| WASHER TIN PLATED BRASS| ANY
7| 2| J7, J8| CONN BNC 5 PINS| CONNEX 112404
8| 2| JP1, JP4| HEADER 2MM SINGLE 3-PIN| SAMTEC TMM-103-02-L-S
9| 2| JP2, JP3| HEADER 2MM SINGLE 4-PIN| SAMTEC TMM-104-02-L-S
10| 2| JP5, JP6| HEADER 2MM SINGLE 3-PIN| SAMTEC TMM-103-02-L-S
11| 1| XJP1-XJP4| SHUNT| SAMTEC 2SN-BK-G
12| 1| XJP5,XJP6| SHUNT| SAMTEC 2SN-BK-G

SCHEMATIC DIAGRAM

DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LT C ) 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 LT C 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 LT C 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. LT C assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. LT C 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 LT C application engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation

12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
408-432-1900
FAX: 408-434-0507
www.linear.com

References

• Mixed-signal and digital signal processing ICs | Analog Devices

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