ANALOG DEVICES EVAL-LTC3313 Evaluation Board User Guide

ANALOG DEVICES EVAL-LTC3313 Evaluation Board

FEATURES

• EVAL-LTC3313EV-A-Z evaluation board
• Transient circuit included for load transient evaluation
• EMI filter included to reduce noise in EMI emission tests
• MODE pin pull-up option for pulse-skipping mode evaluation

EVALUATION KIT CONTENTS

• EVAL-LTC3313EV-A-Z evaluation board

DOCUMENTS NEEDED

• LTC3313 data sheet
• EVAL-LTC3313EV-A-Z user guide

EQUIPMENT NEEDED

• A DC voltage source
• An electronic load
• A multimeter

GENERAL DESCRIPTION

The EVAL-LTC3313EV-A-Z features the LTC3313, 15 A low voltage synchronous step-down Silent Switcher® that operates as a 2 MHz, 2.25 V to 5.5 V input, 1.2 V, 15 A output buck regulator. The LTC3313 supports an output voltage (VOUT) from 0.5 V to the input voltage (VIN) with operating frequencies from 500 kHz up to 5 MHz. The LTC3313 is a compact, ultralow emission, high- efficiency, and high speed synchronous monolithic step-down switching regulator. The Silent Switcher technology optimizes fast-current loops and makes it easier to minimize electromagnetic interference (EMI) and electromagnetic compatibility (EMC) emissions. The minimum on-time of 35 ns typical enables high VIN to low VOUT conversion at a high frequency.

The EVAL-LTC3313EV-A-Z runs in forced continuous mode with a 2 MHz switching frequency (fSW); however, it can be configured to run at different switching frequencies or in pulse-skipping mode. The LTC3313 oscillator can also synchronize to an external clock using a MODE/SYNC turret, with the EVAL- LTC3313EV-A-Z default setup. Figure 4 shows the efficiency and power loss of the EVALLTC3313EV-A-Z with a 3.3 V input in both operation modes. The EVAL- LTC3313EV-A-Z also has an EMI filter to reduce conducted EMI. This EMI filter can be included by applying the input voltage at the VIN EMI terminal. The EMI performance of the boardEVAL-LTC3313EV-A-Z is shown in the EMI Test Results section. The red lines in the EMI performance graphs illustrate the CISPR25 Class 5 peak limits for the conducted and radiated emission tests.

EVALUATION BOARD PHOTOGRAPH

EVAL-LTC3313EV-A-Z Board Photograph

The LTC3313 data sheet gives a complete description of the device and its application information. The data sheet must be read in conjunction with this evaluation board user guide. The LTC3313 is assembled in a 3 mm × 3 mm LQFN package with an exposed pad for low thermal resistance. The layout recommendations for low EMI operation and maximum thermal performance are available in the LTC3313 data sheet.

PERFORMANCE SUMMARY

TA = 25°C. Table 1. Performance Summary

Parameter/ Test Conditions/Comments/ Min/ Typ/ Max/ Unit

EVALUATION BOARD HARDWARE

INTRODUCTION TO THE EVAL-LTC3313EV-A-Z The EVAL-LTC3313EV-A-Z evaluation board features the LTC3313, a low voltage, synchronous step-down Silent Switcher. The LTC3313 is a monolithic, constant frequency, current mode stepdown DC/DC converter. An oscillator turns on the internal top power switch at the beginning of each clock cycle. Current in the inductor then increases until the top switch comparator trips and turns off the top power switch. The peak inductor current, at which the top switch turns off, is controlled by the voltage on the ITH node.

The error amplifier servos the ITH pin by comparing the voltage on the internal VFB pin with an internal 500 mV reference. When the load current increases, it causes a reduction in the feedback voltage relative to the reference, leading the error amplifier to raise the ITH voltage until the average inductor current matches the new load current. When the top switch turns off, the synchronous bottom power switch turns on until the next clock cycle begins. In pulse-skipping mode, the bottom switch also turns off when inductor current falls to zero. If overload conditions result in excessive current flowing through the bottom switch, the next clock cycle will be delayed until the switch current returns to a safe level. If the EN pin is low, the LTC3313 is in a shutdown state with a low quiescent current. When the EN pin is more than its threshold, the switching regulator enables.

The MODE/SYNC pin synchronizes the switching frequency to an external clock that can be a clock output for multiphase operation. The MODE/SYNC pin also sets the regulator operation modes. The operation modes are either forced continuous or pulse-skipping. See the LTC3313 data sheet for more detailed information. The maximum allowable operating frequency (fSW(MAX)) is influenced by the minimum on time (tON(MIN)) of the top switch, the ratio of VOUT to VIN and the inductance of the output inductor.

Use the following equation to calculate the maximum allowable operating frequency:

LTC3313, 1.2 V/15 A Step-Down Converter Typical Solution

Select an operating switching frequency below fSW(MAX). It is desired to obtain an inductor current of 30% of the maximum LTC3313 operating load, 15 A.

Use the following equations to calculate the inductor value to obtain a 30% (4.5 A) inductor ripple for the operating frequency:

When determining the compensation components, C4, C10, C24, and R12, controlling the loop stability and transient response are the two main considerations. The LTC3313 was designed to operate at a high bandwidth for fast transient response capabilities, which reduces the required output capacitance to meet the desired transient voltage range. The midband gain of the loop increases with R12 and the bandwidth of the loop increases by decreasing C24. C4 and R9 provide a phase lead that improves the phase margin. C10 and R12 provide a high-frequency pole to reduce the high-frequency gain.

Loop stability is generally measured using the Bode plot method of plotting loop gain in decibels and phase shift in degrees. The 0 dB crossover frequency must be less than 1/6 of the operating frequency to reduce the effects of the added phase shift of the modulator. The control-loop phase margin goal must be 45º or greater, and the gain margin goal must be 8 dB or greater.

QUICK START PROCEDURE

Before following the quick start procedure, note that for accurate VIN, VOUT, and efficiency measurements, measure VIN at the VIN SNSE and GND SNSN turrets and measure VOUT at the VOUT SNSE and GND SNSE turrets, which are illustrated as VM1 and VM2 in Figure 6. In addition, when measuring the input or output ripple, avoid a long ground lead on the oscilloscope probe.

Refer to Figure 6 for the proper measurement equipment test setup and also take the following steps:

1. Set the JP1 jumper to the HI position.
2. With power off, connect the input power supply to VIN and GND. If the input EMI filter is desired, connect the input power supply to VIN EMI and GND.
3. Set the power supply (PS1) current limit to 10 A.
4. Set the electronic load (LD1) to CC mode and a 0 A current.
5. Slowly increase PS1 to 1.0 V. If the PS1 output current reads less than 20 mA, increase PS1 to 3.3 V.
6. Verify that VM1 reads 3.3 V and that VM2 reads approximately 1.2 V.
7. Check VM1, VM2, VM3, the PS1 output current, and the LD1 input current.
8. Connect an oscilloscope voltage probe as shown in Figure 7 or Figure 8.
9. Set the channel to AC-coupled, the voltage scale to 20 mV, and the time base to 10 µs. Also, check the VOUT ripple and verify that the PGOOD voltage is more than 3 V.
10. Increase the load by 1 A intervals up to 15 A and observe the voltage output regulation, ripple voltage, and the voltage on the SSTT turret.
11. Use the following equation to calculate the die temperature:
12. If pulse-skipping mode is desired, set PS1 to 0 V, install a 0 Ω resistor in the R3 location, and remove R6. Repeat Step 1 through Step 11. In step 11, observe that the switching waveform is now in pulse-skipping mode at light load.
13. Optionally, to change the frequency, remove R3 and R4, if installed. Install the desired RT resistor in the R7 location. Note that the MODE/SYNC pin must have high impedance to GND and VIN. Size the inductor, output capacitors, and compensation components to provide the desired inductor ripple and a stable output. Refer to the LTC3313 data sheet and LTpowerCAD for more information on choosing the required components.
14. To test the transient response with a base load, add the desired resistor to produce a minimum load between the VOUT and the I_STEP turrets (RL shown on Figure 6). Note that the total load resistance is RL + R14 (20 mΩ). Adjust a signal generator with a 10 ms period, a 10% duty cycle, and an amplitude from 1 V to 2 V to start.
15. Measure the I_STEP voltage to observe the current, VI_STEP /20 mΩ. Adjust the amplitude of the pulse to provide the desired transient. Connect the signal generator (SG_INPUT) between the SG_INPUT and GND turrets. Adjust the rising and falling edge of the pulse to provide the desired ramp rate. Figure 5 shows a load step from 5 A to 10 A. Refer to the following equations:
16. . When done, turn off SG_INPUT, PS1, and the load, and remove all the connections to the EVAL-LTC3313EV-A-Z.

TYPICAL PERFORMANCE CHARACTERISTICS

Start-Up Waveforms with Light Load (ILOAD Is the Load Inductance.)

Load Step Response

. Efficiency vs. Load Current

TEST SETUP

Test Setup for EVAL-LTC3313EV-A-Z

Technique for Measuring Output Ripple and Step Response with a Scope Probe

Technique for Measuring Output Ripple and Step Response with a Low Inductance Connector (Not Supplied)

EMI TEST RESULTS

EVAL-LTC3313EV-A-Z CISPR25 Conducted Emission with Class 5 Peak Limits (Voltage Method)

EVAL-LTC3313EV-A-Z CISPR25 Radiated Emission (Vertical)

EVAL-LTC3313EV-A-Z CISPR25 Radiated Emission (Horizontal)

EVALUATION BOARD SCHEMATIC

EVAL-LTC3313EV-A-Z Evaluation Board Schematic

ORDERING INFORMATION

BILL OF MATERIALS Table 2. Bill of Materials

Quantity/ Circuit Component/ Description/ Manufacturer/Part Number

Required|  |  |
---|---|---|---
4| C2, C3, C21, C22| 10 μF ceramic capacitors, 6.3 V, 20%, X7S, 0603, low| TDK, C1608X7S0J106M080AC
 |  | effective series resistance (ESR)|
1| C4| 47 pF ceramic capacitor, 50 V, 5%, C0G, 0402, AEC-| Murata, GCM1555C1H470JA16D
 |  | Q200|
2| C5, C6| 47 μF capacitors, X7S, 6.3 V, 20%,1206| TDK, C3216X7S0J476M160AC
3| C8, C19, C20| 1 μF ceramic capacitors, 6.3 V, 20%, X7T, 0201| Murata, GRM033D70J105ME01D
1| C9| 0.033 μF ceramic capacitor, 25 V, 10%, X7R, 0402,| Murata, GCM155R71E333KA55D
 |  | AEC-Q200|
1| C12| 2.2 μF ceramic capacitor, 10 V, 10%, X7S, 0402,| Murata, GRT155C71A225KE13D
 |  | AEC-Q200|
1| C24| 470 pF ceramic capacitor, 50 V, 5%, C0G, 0402| Murata, GRM1555C1H471JA01D
1| L1| 0.08 μH inductor, power shielded, 20%, AEC-Q200| Coilcraft, XEL4020-800MEC
1| R9| 140 kΩ resistor, surface-mounted device (SMD), 1%,| Vishay, CRCW0402140KFKED
 |  | 1/16 W, 0402, AEC-Q200|
1| R10| 100 kΩ resistor, SMD, 1%, 1/10 W, 0402, AEC-Q200| Panasonic, ERJ- 2RKF1003X
1| R12| 4.99 kΩ resistor, SMD, 1%, 1/10 W, 0402, AEC-Q200| Panasonic, ERJ- 2RKF4991X
1| U1| 5 V, 15 A, synchronous step-down Silent Switcher in| Analog Devices, Inc., LTC3313EV#PBF
 |  | 3 mm x 3 mm LQFN|
Additional|  |  |
2| C1, C18| 470 μF tantalum capacitors, 6.3 V, 20%, 7343-40,| Kemet, T530Y477M006ATE005
 |  | very low ESR, 0.005 Ω|
2| C7, C15| 0.1 μF ceramic capacitors, 16 V, 10%, X7R, 0402,| Murata, GCM155R71C104KA55D
 |  | AEC-Q200|
1| C11| 0.1 μF ceramic capacitor, 50 V, 10%, X7R, 0402,| TDK, CGA2B3X7R1H104K050BB
 |  | AEC-Q200, low ESR|
4| C13, C14, C16, C17| 10 μF ceramic capacitors, 6.3 V, 20%, X7R, 0603| Samsung, CL10B106MQ8NRNC
2| C25, C26| 0.22 μF ceramic capacitors, 6.3 V, 20%, X7R, 0603,| Johanson Dielectrics, 6R3X14W224MV4T
 |  | feed through|
2| C27, C28| 10 μF ceramic capacitors, 6.3 V, 20%, X7S, 0603, low| TDK, C1608X7S0J106M080AC
 |  | ESR|
1| C29| 2.2 μF ceramic capacitor, 10 V, 10%, X7S, 0402,| Murata, GRT155C71A225KE13D
 |  | AEC-Q200|
1| L2| Inductor, EMI, ferrite bead, 8 A| Wurth Elektronik, 74279226101
1| Q1| Transistor, metal-oxide semiconductor field-effect| Infineon, BSC010NE2LSIATMA1
 |  | transistor (MOSFET), N channel, 25 V, 38 A, 8-lead|
 |  | TDSON, EP|
1| R1| 1 MΩ resistor, SMD, 1%, 1/16 W, 0402, AEC-Q200| Vishay, CRCW04021M00FKED
1| R2| 249 kΩ resistor, SMD, 1%, 1/16 W, 0402, AEC-Q200| Stackpole, RMCF0402FT249K
1| R4| 0 Ω resistor, SMD, jumper, 1/10 W, 0402, AEC-Q200| Panasonic, ERJ- 2GE0R00X
2| R6, R11| 100 kΩ resistors, SMD, 5%, 1/16 W, 0402, AEC-Q200| Vishay, CRCW0402100KJNED
1| R8| 20 Ω resistor, SMD, 1%, 1/10 W, 0402, AEC-Q200| Panasonic, ERJ- 2RKF20R0X
1| R14| 0.02 Ω resistor, SMD, 1%, 10 W, 2818, AEC-Q200| Vishay, WSHP2818R0200FEA
1| R15| 10 kΩ resistor, SMD, 5%, 1/16 W, 0402, AEC-Q200| Vishay, CRCW040210K0JNED
1| J1| Connector, U.FL, receptor, straight, SMD, 0 Hz to 6| Hirose Electric, U.FL-R-SMT-1(10)
 |  | GHz, 50 Ω|
Required Hardware 11| ****

TP1 to TP3, TP5, TP12, TP14 to TP17, TP20, TP21

| ****

Printed circuit board (PCB) connectors, solder terminal turrets for clip leads

| ****

Mill-Max, 2308-2-00-80-00-00-07-0

Table 2. Bill of Materials (Continued)

5| TP4, TP7, TP10, TP13, TP18| PCB connectors, solder terminal turrets| Mill- Max, 2501-2-00-80-00-00-07-0
---|---|---|---
5| TP6, TP8, TP9, TP11, TP19| PCB connectors, banana jack| Keystone Electronics, 575-4
1| JP1| Connector, header, male, 1 x 3, 2 mm, vertical,| Wurth Elektronik, 62000311121
 |  | straight,THT|
4| MP1 to MP4| Standoffs, nylon, snap-on, 0.50″| Keystone Electronics, 8833
1| XJP1| Connector, shunt, female, 2-position, 2 mm| Wurth Elektronik, 60800213421

ESD Caution ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.

Legal Terms and Conditions By using the evaluation board discussed herein (together with any tools, components documentation or support materials, the “Evaluation Board”), you are agreeing to be bound by the terms and conditions set forth below (“Agreement”) unless you have purchased the Evaluation Board, in which case the Analog Devices Standard Terms and Conditions of Sale shall govern. Do not use the Evaluation Board until you have read and agreed to the Agreement. Your use of the Evaluation Board shall signify your acceptance of the Agreement. This Agreement is made by and between you (“Customer”) and Analog Devices, Inc. (“ADI”), with its principal place of business at Subject to the terms and conditions of the Agreement, ADI hereby grants to Customer a free, limited, personal, temporary, non-exclusive, non-sublicensable, non- transferable license to use the Evaluation Board FOR EVALUATION PURPOSES ONLY. Customer understands and agrees that the Evaluation Board is provided for the sole and exclusive purpose referenced above, and agrees not to use the Evaluation Board for any other purpose. Furthermore, the license granted is expressly made subject to the following additional limitations: Customer shall not (i) rent, lease, display, sell, transfer, assign, sublicense, or distribute the Evaluation Board; and (ii) permit any Third Party to access the Evaluation Board. As used herein, the term “Third Party” includes any entity other than ADI, Customer, their employees, affiliates and in-house consultants. The Evaluation Board is NOT sold to Customer; all rights not expressly granted herein, including ownership of the Evaluation Board, are reserved by ADI. CONFIDENTIALITY. This Agreement and the Evaluation Board shall all be considered the confidential and proprietary information of ADI. Customer may not disclose or transfer any portion of the Evaluation Board to any other party for any reason.

Upon discontinuation of use of the Evaluation Board or termination of this Agreement, Customer agrees to promptly return the Evaluation Board to ADI. ADDITIONAL RESTRICTIONS. Customer may not disassemble, decompile or reverse engineer chips on the Evaluation Board. Customer shall inform ADI of any occurred damages or any modifications or alterations it makes to the Evaluation Board, including but not limited to soldering or any other activity that affects the material content of the Evaluation Board. Modifications to the Evaluation Board must comply with applicable law, including but not limited to the RoHS Directive.

TERMINATION. ADI may terminate this Agreement at any time upon giving written notice to Customer. Customer agrees to return to ADI the Evaluation Board at that time. LIMITATION OF LIABILITY. THE EVALUATION BOARD PROVIDED HEREUNDER IS PROVIDED “AS IS” AND ADI MAKES NO WARRANTIES OR REPRESENTATIONS OF ANY KIND WITH RESPECT TO IT. ADI SPECIFICALLY DISCLAIMS ANY REPRESENTATIONS, ENDORSEMENTS, GUARANTEES, OR WARRANTIES, EXPRESS OR IMPLIED, RELATED TO THE EVALUATION BOARD INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTY OF MERCHANTABILITY, TITLE, FITNESS FOR A PARTICULAR PURPOSE OR NONINFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS. IN NO EVENT WILL ADI AND ITS LICENSORS BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT, OR CONSEQUENTIAL DAMAGES RESULTING FROM CUSTOMER’S POSSESSION OR USE OF THE EVALUATION BOARD, INCLUDING BUT NOT LIMITED TO LOST PROFITS, DELAY COSTS, LABOR COSTS OR LOSS OF GOODWILL. ADI’S TOTAL LIABILITY FROM ANY AND ALL CAUSES SHALL BE LIMITED TO THE AMOUNT OF ONE HUNDRED US DOLLARS ($100.00). EXPORT.

Customer agrees that it will not directly or indirectly export the Evaluation Board to another country, and that it will comply with all applicable United States federal laws and regulations relating to exports. GOVERNING LAW. This Agreement shall be governed by and construed in accordance with the substantive laws of the Commonwealth of Massachusetts (excluding conflict of law rules). Any legal action regarding this Agreement will be heard in the state or federal courts having jurisdiction in Suffolk County, Massachusetts, and Customer hereby submits to the personal jurisdiction and venue of such courts. The United Nations Convention on Contracts for the International Sale of Goods shall not apply to this Agreement and is expressly disclaimed.

References

• Mixed-signal and digital signal processing ICs | Analog Devices
• LTC3313 Datasheet and Product Info | Analog Devices

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