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8.Dec.2015 - Rev.001

ROHM Switching Regulator Solutions

Evaluation Board for ROHM's BD9E151NUX non-Synchronous Buck Converter with Integrated FET BD9E151NUX-E2EVK-101 (5.0V | 1.2A Output)

Introduction

This application note will explain the steps necessary to operate and evaluate ROHM’s BD9E151NUX non-synchronous buck DC/DC converter using the BD9E151NUX-E2EVK-101 evaluation board. Component selection, board layout recommendations, operating procedures, and application data are included.

Description

This evaluation board has been specifically developed to evaluate the BD9E151NUX non-synchronous buck DC/DC converter with integrated 80mΩ high-side MOSFET. Features include wide input (6.0 to 28.0V) and output (1.0V to 23.0V) voltage ranges and a fixed operating frequency of 600kHz. Multiple protection functions are also built in, including a fixed soft start circuit that prevents inrush current during startup, UVLO (Under Voltage Lock Out), TSD (Thermal Shutdown), OCP (Over Current Protection), and OVP (Over Voltage Protection). An EN pin allows for simple ON/OFF control to reduce standby current consumption.

Applications

Surveillance Cameras

OA Equipment

12V/24V Distributed Power Systems

Evaluation Board Operating Limits and Absolute Maximum Ratings

Parameter Symbol Limit

Unit Conditions MIN TYP MAX

Supply Voltage

BD9E151NUX VCC 6.0 - 28.0 V

Output Voltage / Current

BD9E151NUX

VOUT 1.0(*2)

- VINx0.7

or VIN-5

(*3)

V * Set by R1 and R2

IOUT - - 1.2 A

(*2)Limited by the minimum pulse width (typ. 100ns)

(*3)Limited by BSTUVLO or Max Duty Cycle (ref. page.8). Please set value of the low one for the maximum.

Evaluation Board

Below is an image of the BD9E151NUX-E2EVK-101 evaluation board.

AEY58-D1-0014

GND Vout BD9673EFJ Eval Board EN

Fig 1: BD9E151NUX-E2EVK-101 Evaluation Board

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8.Dec.2015 - Rev.001

Board Schematic

Board I/O

Below is a reference application circuit that shows the inputs VIN, EN, and the output VOUT.

Operating Procedures

1. Connect the power supply’s GND terminal to GND test point TP2 on the evaluation board. 2. Connect the power supply’s VCC terminal to VIN test point TP1 on the evaluation board. This will provide VIN to the IC U1.

Please note that VCC should be in the range from 6V to 28V. 3. Check that the shunt jumper J1 is in the ON position (connect Pin 2 to Pin 1, the EN pin of IC U1 is pulled high). 4. Connect the electronic load to TP3 and TP4. Do not turn the load ON. 5. Turn ON the power supply. The output voltage VOUT (+5V) can be measured at test point TP3. Now turn the load ON. The load

can be increased up to 1.2A MAX.

Notes:

This board does not support hot plugging. Therefore, please NO NOT hot plug the power supply.

Fig 2: BD9E151NUX-E2EVK-101 Evaluation Board Schematic

Fig 3: Evaluation Board I/O

C1: 0.1uF

C6: 10uF/35V

L1: 15uH

C2, C3: 22uF/16V(total 44uF)

D1

C9: 0.047uF R2: 3kΩ

R1: 12kΩ

BST

VIN

EN

SS

LX

GND

VC

FB

VIN

C8: 10000pF

R3: 2.7kΩ

1

2

3

4

8

7

6

5

VOUT

EN

C10:open

RO: 1kΩ ( )

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8.Dec.2015 - Rev.001

Reference Application Data

The following are graphs of the quiescent current, efficiency, load response, and output voltage ripple response of the BD9E151NUX-E2EVK-101 evaluation board.

Fig 4: Circuit Current vs. Power Supply Voltage (VIN =

0-28V, Temp=25oC)

Fig 5: Electric Power Conversion Rate

(Vin=12V, VOUT=5V)

Fig 8: Output Voltage Ripple Response Characteristics (VIN=12V, VOUT=5V, IOUT=0A)

Fig 9: Output Voltage Ripple Response Characteristics (VIN=12V, VOUT=5V, IOUT=1.2A)

Fig 6: Load Response Characteristics (VIN=12V, VOUT=5V, IOUT=0A 1.2A)

Fig 7: Load Response Characteristics (VIN =12V, VOUT =5V, IOUT =1.2A 0A)

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8.Dec.2015 - Rev.001

Evaluation Board Layout Guidelines

The following guidelines are recommended for BD9E151NUX designs.

Layout is a critical element of good power supply design. There are several signals paths that conduct fast-changing currents or

voltages that can interact with stray inductances and parasitic capacitances to generate noise or degrade power supply

performance. To help eliminate these problems, the VIN pin should be bypassed to ground with a low ESR ceramic bypass

capacitor with B dielectric. Care should be taken to minimize the loop area formed by the bypass capacitor connections, the

VIN pin, and the anode of the catch diode. See Fig. 10 for a PCB layout example.

In the BD9E151NUX, since the LX connection is the switching node, the catch diode and output inductor should be located close

to the LX pins and the area of the PCB conductor minimized to prevent excessive capacitive coupling. In addition, the GND area

should not be connected directly to power GND or high current switch paths. The extra external components can be placed

approximately as shown.

Fig 10: BD9E151NUX-E2EVK-101 PCB Layout

Fig 11: Evaluation Board Layout

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8.Dec.2015 - Rev.001

Application Circuit Component Selection

(1) Inductor

A shield type inductor with low DCR (DC resistance component) that satisfies the current rating (current value I

PEAK below) is recommended.

The inductance value has a significant effect on the inductor ripple current, which becomes the source of output ripple. As shown in the formula below, this ripple current can be minimized by increasing the switching frequency and/or the L value of the coil.

𝐈𝐏𝐄𝐀𝐊 = 𝐈𝐎𝐔𝐓 +⊿𝐈𝐋

𝟐 … (𝟏)

⊿𝐈𝐋 =𝐕𝐈𝐍−𝐕𝐨𝐮𝐭

𝐋×

𝐕𝐎𝐔𝐓

𝐕𝐈𝐍×

𝟏

𝐟 … (𝟐)

Where ΔL = Output Ripple Current, VIN = Input Voltage, VOUT = Output Voltage, and f = Switching Frequency

For the inductor ripple current, please carry out design with a target of 20-50% of the maximum input current.

(2) Output Capacitor

To reduce output ripple voltage, a low ESR ceramic capacitor is recommended. And in addition to taking into account DC bias characteristics, please provide sufficient margin with respect to the absolute maximum rated output voltage. The permissible output ripple voltage can be determined using the formula below. And although the actual value of the output capacitor is not critical, some practical limits do exist. Consider the relationship between the crossover frequency of the design and LC corner frequency of the output filter. In general, it is desirable to restrict the crossover frequency to less than 1/5 of the switching frequency. With high switching frequencies such as 600kHz in this case, the internal circuit limitations of the BD9E151NUX limit the practical maximum crossover frequency to about 30kHz. In general, the crossover frequency should be higher than the corner frequency determined by the load impedance and the output capacitance. This limits the minimum capacitor value of the output filter to:

𝐂𝐎𝐔𝐓_𝐦𝐢𝐧 =𝟏

𝟐𝛑×𝐑𝐥×𝐟𝐜_𝐦𝐚𝐱 . . . (3)

Where Rl is the Output Load Resistance and fc_max is the Maximum Crossover Frequency. The output ripple voltage can be estimated by:

𝐕𝐏𝐏 =⊿𝐈𝐋 ×𝟏

𝟐𝛑×𝐟×𝐂𝐎𝐔𝐓+⊿𝐈𝐋 × 𝐑𝐄𝐒𝐑 . . . (4)

Please implement design such that the ripple voltage limit is not exceeded.

For the BD9E151NUX a ceramic capacitor greater than 10uF is recommended.

(3) Output Voltage Setting

The internal reference voltage of the Error Amp is 1.0V. The output voltage is determined by:

𝐕𝐎𝐔𝐓 =𝐑𝟏+ 𝐑𝟐

𝐑𝟐 . . . (5)

(4) Bootstrap Capacitor

Please connect from a laminate ceramic capacitor within the range of 0.047uF to 0.47uF between the BST and LX pins.

Fig 12: Inductor Current

Fig 13: Output Voltage Setting

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8.Dec.2015 - Rev.001

(5) Soft Start Function

We highly recommend connecting an external capacitor C9 between the SS and GND pins in order to prevent inrush current during startup, since soft start is not implemented internally. The BD9E151NUX has an internal pull-up current source of 2uA that charges the external soft start capacitor. The equation for the soft start time (10% to 90%) is shown in the following equation. Here the Iss current is 2uA.

𝐓𝐒𝐒 =𝐂𝟗× 𝟎.𝟖

𝐈𝐬𝐬. . . (6)

(6) Catch Diode

The BD9E151NUX requires that an external catch diode be connected between LX and GND. The selected diode must meet the absolute maximum ratings for the application. The reverse voltage must be higher than the maximum voltage at the LX pin,

(VINMAX + 0.5V). Peak current must be greater than IOUTMAX+⊿IL, while the forward voltage drop should be small to enable higher

efficiencies. It is also important to note that the catch diode conduction time is typically longer than the high-side FET ON time, so paying careful attention to diode parameters can make a marked improvement in overall efficiency. Additionally, check that the device chosen is capable of dissipating the power losses.

(7) Input Capacitor

Depending on the application, an input capacitor may be required. Use low ESR capacitors for optimal performance. Ceramic capacitors are preferred, but low-ESR electrolytic capacitors may also suffice. The typical recommended value for the decoupling capacitor is 10uF. Please place this capacitor as close as possible to the VIN pin. When using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input. The input voltage ripple caused by capacitance can be estimated by:

∆𝐕𝐂𝐂=𝐈𝐎𝐔𝐓

𝐟×𝐂𝐕𝐂𝐂×

𝐕𝐎𝐔𝐓

𝐕𝐂𝐂× [𝟏 −

𝐕𝐎𝐔𝐓

𝐕𝐂𝐂] . . . (7)

Since the input capacitor (CVIN) absorbs the input switching current, an adequate ripple current rating is required. The RMS current in the input capacitor can be calculated by:

𝐈𝐂𝐕𝐂𝐂 = 𝐈𝐎𝐔𝐓 × √𝐕𝐎𝐔𝐓

𝐕𝐂𝐂× (𝟏 −

𝐕𝐎𝐔𝐓

𝐕𝐂𝐂) . . . (8)

The worst case condition occurs at VIN= 2VOUT, where

𝐈𝐂𝐕𝐂𝐂_𝐦𝐚𝐱 =𝐈𝐎𝐔𝐓

𝟐 . . . (9)

(8) Adjusting the DC/DC Comparator Frequency Characteristics

Phase compensation elements C8, C10, R3 (refer to Fig. 3: Application Reference Circuit Example) The stability and responsiveness of the loop are controlled through the VC pin which is the output of the error amp. The combination of zero and pole that determines the stability and responsiveness is adjusted by the combination of the resistor and capacitor that are connected in series to the VC Pin. The DC gain and voltage feedback loop can be calculated using the following formula.

𝐀𝐝𝐜 = 𝐑𝐥 × 𝐆𝐂𝐒 × 𝐀𝐄𝐀 ×𝐕𝐅𝐁

𝐕𝐨𝐮𝐭 . . . (10)

Here, VFB is the Feedback Voltage (1.0V), AEA is the Voltage Gain of the Error Amp (60dB typ.), GCS is the Transconductance of the Current Detection Amp (10A/V typ.), and RI is the Output Load Resistance. There are 2 important poles in the control loop of this DC/DC. The first is caused by the phase compensation capacitor (C8) and output resistor of the error amp. The other occurs due to the output capacitor and load resistor. These poles appear in the frequencies noted below.

Fig 14: Soft Start Time Setting

C9

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8.Dec.2015 - Rev.001

𝐟𝐩𝟏 =𝐆𝐄𝐀

𝟐𝛑×𝐂𝟖×𝐀𝐄𝐀 . . . (11)

𝐟𝐩𝟐 =𝟏

𝟐𝛑×𝐂𝐎𝐔𝐓×𝐑𝐥 . . . (12)

Here, GEA is the Transconductance of the Error Amp (250uA/V typ.) In this control loop, one zero becomes important. The zero that occurs due to the phase compensation capacitor C8 and resistor R3 appears in the frequency below.

𝐟𝐳𝟏 =𝟏

𝟐𝛑×𝐂𝟖×𝐑𝟑 . . . (13)

Also, in the event that both the output capacitor and ESR (RESR) are large, there may be cases of another important zero (ESR zero) in the control loop. This ESR zero occurs due to the ESR and capacitance of the output capacitor, and exists in the below frequency.

𝐟𝐳𝐄𝐒𝐑 =1

𝟐𝛑×𝐂𝐎𝐔𝐓×𝐑𝐄𝐒𝐑 . . . (14) (ESR zero)

In this case the 3rd pole determined by the 2nd phase compensation capacitor (C10) and resistor (R3) is used to correct the ESR zero results on the loop gain. This pole exists in the frequency shown below.

𝐟𝐩𝟑 =𝟏

𝟐𝛑×𝐂𝟏𝟎×𝐑𝟑 . . . (15) (Pole that corrects the ESR zero)

The goal of phase compensation design is to create a communication function in order to obtain the necessary band and phase margin. The crossover frequency (band) at which the loop gain of the feedback loop becomes '0' is important. When the crossover frequency decreases the power supply fluctuation response and load response suffer. On the other hand, when the crossover frequency is too high loop instability can occur. Tentatively, a crossover frequency 1/20th of the switching frequency is recommended.

Selection of the phase compensation constants are shown below.

1. The phase compensation resistor (R3) is selected in order to set the desired crossover frequency. Calculation of R3 is performed using the following formula.

𝐑𝟑 =𝟐𝛑×𝐂𝐎𝐔𝐓×𝐟𝐜

𝐆𝐄𝐀×𝐆𝐂𝐒×

𝐕𝐎𝐔𝐓

𝑽𝐅𝐁 . . . (16)

Here, fc is the desired Crossover Frequency, and is set to 1/20th of the normal switching frequency (fosc). 2. The phase compensation capacitor (C8) is selected in order to achieve the desired phase margin. In applications with a typical inductance value (10uH to 22uH), sufficient phase margin can be obtained by matching the phase compensation zero to less than 1/4th the crossover frequency. C8 is calculated using the following formula.

𝐂𝟖 >𝟒

𝟐𝛑×𝐑𝟑×𝐟𝐜 . . . (17)

3. Consideration of whether or not the 2nd phase compensation capacitor (C10) is required. If the ESR zero of the output capacitor is less than half the switching frequency, a second phase compensation capacitor will be required, determined using the following formula.

𝟏

𝟐𝛑×𝐂𝐎𝐔𝐓×𝐑𝐄𝐒𝐑<

𝐟𝐬

𝟐 . . . (18)

In this case add the second phase compensation capacitor (C10) and match the third pole frequency (fp3) to the frequency of ESR zero. C10 is calculated using the formula below.

𝐂𝟏𝟎 =𝐂𝐎𝐔𝐓×𝐑𝐄𝐒𝐑

𝐑𝟑 . . . (19)

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8.Dec.2015 - Rev.001

Output Voltage Limit

To prevent malfunctions of the Nch FET driver block, the BD9E151NUX integrates a circuit (BSTUVLO) that prevents malfunction due to low voltage input between the BST and LX pins. As a result, the output voltage is limited by BSTUVLO and the max. duty cycle (85% min.).

① Limiting by BSTUVLO

When BSTUVLO operates, the high-side FET is turned OFF and charge is supplied from VIN to BST in order to maintain the voltage between the BST and LX pins (Path 1). The following formula must be satisfied to reset BSTUVLO.

𝐕𝐈𝐍 ≥ 𝐕𝐈𝐍 + 𝐕𝐅 + 𝐁𝐒𝐓𝐔𝐕𝐋𝐎 𝐫𝐞𝐬𝐞𝐭 … (20)

Where BSTUVLO reset is the BSTUVLO Reset Voltage and VF is the Diode Forward Bias between the VIN and BST pins. Considering fluctuations in the BSTUVLO reset voltage and VF from the above equation, even at maximum the voltages will be less than 5V, so the max. value of the output voltage is defined as VIN-5V.

② Limiting by the Max. Duty Cycle

The max. output voltage is limited by the max. duty cycle (85% min.). At this time, the effects of the Nch FET ON resistance, output current, and forward voltage (VF) of the catch diode must be considered. The max. output voltage can be calculated using the following formula.

𝐕𝐎𝐔𝐓_𝐦𝐚𝐱 = (𝐕𝐈𝐍 − 𝐑𝐎𝐍 × 𝐈𝐎𝐔𝐓) × 𝟎. 𝟖𝟓 − 𝐕𝐅 × 𝟎. 𝟏𝟓 … (21)

However, considering the effects from inductor loss and possible voltage fluctuations based on the type of catch diode, the max. output voltage is defined as VIN x 0.7. Therefore, please set a max. output voltage using the lower max. value from the above limitations.

We recommend connecting the resistor 1kΩbetween Vout and GND when VIN is lower 7V shown as Figure.3.

Fig 15: BST Charge Path

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8.Dec.2015 - Rev.001

Evaluation Board BOM

Below is a table showing the bill of materials. Part numbers and supplier references are also provided.

Item Qty. Ref Description Manufacturer Part Number

1 1 C1 CAP CER 0.1UF 16V 10% X7R 0603 Murata GRM188R71C104KA01D

2 2 C2,C3 CAP CER 22UF 16V 20% X7R 1210 Murata GRM32ER71C226MEA8

3 1 C6 CAP CER 10UF 35V 10% X5R 1206 Murata GRM31CR6YA106KA12L

4 1 C8 CAP CER 10000PF 50V 10% X7R 0402 Murata GRM155R71H103KA88D

5 1 C9 CAP CER 0.047UF 25V 10% X7R 0402 Murata GRM155R71E473KA88D

6 1 D1 DIODE SCHOTTKY 30V 1A 2TUMD ROHM RSX101VA-30TR

7 1 J1 CONN HEADER VERT .100 3POS 15AU FCI 68000-103HLF

8 1 L1 INDUCTOR POWER 15UH 2.2A SMD Wurth Electronics 7447713150

9 1 R1 RES 12K OHM 1/10W 1% 0603 SMD ROHM MCR03ERTF1202

10 1 R2 RES 3K OHM 1/10W 1% 0603 SMD ROHM MCR03ERTF3001

11 1 R3 RES 2.7K OHM 1/10W 1% 0603 SMD ROHM MCR03ERTF2701

12 2 TP1,TP3 TEST POINT PC MULTI PURPOSE RED Keystone Electronics 5010

13 2 TP2,TP4 TEST POINT PC MULTI PURPOSE BLK Keystone Electronics 5011

14 1 U1 IC REG BUCK ADJ 1.2A 8VSON ROHM BD9E151NUX-TR

15 1 Shunt jumper for header J1 (item #8), CONN SHUNT 2POS GOLD W/HANDLE

TE Connectivity 881545-1

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8.Dec.2015 - Rev.001

Notes

No copying or reproduction of this document, whole or in part, is permitted without the consent of ROHM Co., Ltd. The contents specified herein are subject to change without notice. The information contained in this document are for the purpose of introducing ROHM products (hereinafter "Products"). When using any such Products, please be sure to refer to the specifications, which can be obtained from ROHM upon request. Examples of application circuits, circuit constants and any other information contained herein illustrate the standard usage and operation of the Products, and peripheral conditions must be taken into account when designing circuits for mass production. Great care was taken in ensuring the accuracy of the information specified in this document. However, ROHM shall bear no responsibility for any damages incurred from inaccuracies or the misprint of information. The technical information specified herein is intended only to show the typical functions and examples of application circuits for the Products. ROHM does not grant, either explicitly or implicitly, any license to use or exercise intellectual property or other rights held by ROHM and other parties. And ROHM shall bear no responsibility whatsoever for any disputes arising from the use of such technical information. The Products specified in this document are intended to be used with general-use electronic equipment or devices (such as audio visual equipment, office automation equipment, communication devices, electronic appliances, and gaming systems). The Products specified in this document are not designed to be radiation tolerant. While ROHM makes every effort to enhance the quality and reliability of its Products, Products may fail or malfunction for a variety of reasons. Please be sure to implement safety measures to guard against the possibility of physical injury, fire or any other damage that may arise due to Product failure, such as derating, redundancy, fire control and fail-safe designs. ROHM shall bear no responsibility whatsoever for the use of any Product outside of the prescribed scope or not in accordance with the instruction manual. The Products are not designed or manufactured to be used with any equipment, device or system which requires an extremely high level of reliability, the failure or malfunction of which may result in a direct threat to human life or create a risk of human injury (such as a medical instruments, transportation equipment, aerospace machinery, nuclear reactor controllers, fuel controllers, or other safety device). ROHM shall bear no responsibility in any way for the use of any Products for the above special purposes. If a Product is to be used for any such special purpose, please contact a ROHM sales representative before purchasing. If intending to export or ship overseas any Product or technology specified herein that is controlled under the Foreign Exchange and Foreign Trade Law it may be necessary to obtain a license or permit under the applicable law.

Thank you for your interest in ROHM products. Please contact us for additional information or product catalogs.

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