LM34919BEVAL/NOPB

User's Guide SNVA418A – May 2010 – Revised April 2013 AN-2016 LM34919B Evaluation Board 1 Introduction The LM34919BEVAL evaluation board provides the design engineer with a fully functional buck regulator, employing the constant on-time (COT) operating principle. This evaluation board provides a 3.3V output over an input range of 6V to 24V. The circuit delivers load currents to 600 mA, with current limit set at a nominal 800 mA. The board is populated with all components except R5, C9 and C10. These components provide options for managing the output ripple as described later in this document. The board’s specification are: • Input Voltage: 6V to 24V • Output Voltage: 3.3V • Maximum load current: 600 mA • Minimum load current: 0A • Current Limit: 780 mA to 815 mA • Measured Efficiency: 88.7% (VIN = 6V, IOUT = 300 mA) • Nominal Switching Frequency: 1.5 MHz • Size: 2.6 in. x 1.6 in. x 0.5 in All trademarks are the property of their respective owners. SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated 1 Theory of Operation www.ti.com P/N 551600404-001 Rev A (c)2009 NSC LM34919B EVALUATION BOARD National Semiconductor OUT J5 C 10 R4 GND IN R1 U1 C2 C1 R3 C6 J2 D1 C7 C5 R5 J1 J4 R6 C8 J 3 GND L1 MADE IN U.S. 980600404 Note: R2, C3, C4, and C9 are located on board's back side. Figure 1. Evaluation Board - Top Side 2 Theory of Operation Figure 1 shows the evaluation board schematic, which contains a simplified block diagram of the LM34919B. When the circuit is in regulation, the buck switch is on each cycle for a time determined by R1 and VIN according to Equation 1: tON = 0.565 x 10 -10 x (R1 + 1.4 k:) VIN - 1.5V + 55 ns (1) The on-time of this evaluation board ranges from ≊424 ns at VIN =6V, to ≊129 ns at VIN = 24V. The on-time varies inversely with VIN to maintain a nearly constant switching frequency. At the end of each on-time the Minimum Off-Timer ensures the buck switch is off for at least 88 ns. In normal operation, the off-time is much longer. During the off-time, the load current is supplied by the output capacitor (C7, C8). When the output voltage falls sufficiently that the voltage at FB is below 2.5V, the regulation comparator initiates a new on-time period. For stable, fixed frequency operation, a minimum of 25 mV of ripple is required at FB to switch the regulation comparator. The current limit threshold is ≊780 mA at VIN = 6V, and ≊812 mA at VIN = 24V. The variation is due to the change in ripple current amplitude as VIN varies. for a more detailed block diagram, and a complete description of the various functional blocks, see the LM34919B, LM34919B-Q1 Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator Data Sheet (SNVS623). 2 AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback Board Layout and Probing www.ti.com 3 Board Layout and Probing The pictorial in Figure 1 shows the placement of the circuit components. The following should be kept in mind when the board is powered: • The LM34919B, and diode D1 may be hot to the touch when operating at high input voltage and high load current. • Use CAUTION when probing the circuit at high input voltages to prevent injury, as well as possible damage to the circuit. • At maximum load current (0.6A), the wire size and length used to connect the load becomes important. Ensure there is not a significant drop in the wires between this evaluation board and the load. 4 Board Connection/Start-up The input connections are made to the J1 connector. The load is connected to the J2 (OUT) and J3 (GND) terminals. Ensure the wires are adequately sized for the intended load current. Before start-up a voltmeter should be connected to the input terminals, and to the output terminals. The load current should be monitored with an ammeter or a current probe. It is recommended that the input voltage be increased gradually to 6V, at which time the output voltage should be 3.3V. If the output voltage is correct with 6V at VIN, then increase the input voltage as desired and proceed with evaluating the circuit. DO NOT EXCEED 40V AT VIN. 5 Output Ripple Control The LM34919B requires a minimum of 25 mVp-p ripple at the FB pin, in phase with the switching waveform at the SW pin, for proper operation. The required ripple can be supplied from ripple at VOUT, through the feedback resistors as described in Section 5.1 and Section 5.2, or the ripple can be generated separately (using R5, C9, and C10) in order to keep the ripple at VOUT at a minimum (Section 5.3). 5.1 Option A) Lowest Cost Configuration This evaluation board is supplied with R4 installed in series with the output capacitance (C7, C8). R4 is chosen to generate ≥25 mVp-p at VOUT, knowing that the minimum ripple current in this circuit is ≊140 mAp-p at minimum VIN. Using 0.27Ω for R4, the ripple at VOUT ranges from ≊37 mVp-p to ≊88 mVp-p over the input voltage range. If the application can accept this ripple level, this is the most economical solution. The circuit is shown in Figure 2. See Figure 8. 6V to 24V VIN D1 IN C1 1 PF C2 1 PF LM34919B C3 R1 28k Minimum Off Timer On Timer 0.1PF Gnd RON/SD A1 C6 0.022 PF SS B3 FB A3 VCC C3 VIN BST D3 C5 SW D2 Logic C4 0.1 PF 2.5V 0.022 PF L1 8.2 PH R6 0: 3.3V VOUT D1 ISEN Regulation Comparator A2 Current Limit Detect RTN R2 787: C1 R4 0.27: C7 SGND R3 2.49k B1 C8 10 PF 10 PF Gnd Figure 2. Lowest Cost Configuration SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated 3 Output Ripple Control 5.2 www.ti.com Option B) Intermediate Ripple Configuration This configuration generates less ripple at VOUT than Section 5.1 by the addition of one capacitor (Cff) across R2, as shown in Figure 3. 6V to 24 V VIN D1 IN C1 1 PF C2 1 PF LM34919B C3 R1 28k Minimum Off Timer On Timer 0.1PF Gnd RON/SD A1 C6 0.022 PF C4 0.1 PF VIN BST D3 C5 SW D2 Logic SS B3 VCC C3 2.5V 0.022 PF L1 8.2 PH R6 0: D1 ISEN FB A3 3.3V VOUT Regulation Comparator A2 Current Limit Detect RTN C1 R2 787: Cff 2200 pF R4 0.2: C7 SGND R3 2.49k B1 C8 10 PF 10 PF Gnd Figure 3. Intermediate Ripple Configuration Since the output ripple is passed by Cff to the FB pin with little or no attenuation, R4 can be reduced so the minimum ripple at VOUT is ≊25 mVp-p. The minimum value for Cff is calculated from: Cff t tON (max) x 3 (R2//R3) (2) where tON(max) is the maximum on-time (at minimum VIN), and R2//R3 is the parallel equivalent of the feedback resistors, see Figure 8. 5.3 Option C) Minimum Ripple Configuration To obtain minimum ripple at VOUT, R4 is set to 0Ω, and R5, C9, and C10 are added to generate the required ripple for the FB pin. In this configuration, the output ripple is determined primarily by the ESR of the output capacitance and the inductor’s ripple current. The ripple voltage required by the FB pin is generated by R5, C10, and C9 since the SW pin switches from -1V to VIN, and the right end of C10 is a virtual ground. The values for R5 and C10 are chosen to generate a 50-100 mVp-p triangle waveform at their junction. That triangle wave is then coupled to the FB pin through C9. The following procedure is used to calculate values for R5, C10 and C9. 1) Calculate the voltage VA: VA = VOUT – (VSW x (1 – (VOUT/VIN))) (3) where, VSW is the absolute value of the voltage at the SW pin during the off-time (typically 1V), and VIN is the minimum input voltage. For this circuit, VA calculates to 2.84V. This is the approximate DC voltage at the R5/C10 junction, and is used in Equation 4. 2) Calculate the R5 x C10 product: R5 x C10 = (VIN ± VA) x tON 'V (4) where, tON is the maximum on-time (≊424 ns), VIN is the minimum input voltage, and ΔV is the desired ripple amplitude at the R5/C10 junction, 50 mVp-p for this example. R5 x C10 = 4 (6V ± 2.84V) x 424 ns = 26.8 x 10-6 0.05V AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated (5) SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback Monitor The Inductor Current www.ti.com R5 and C10 are then chosen from standard value components to satisfy the above product. Typically C10 is 3000 to 5000 pF, and R5 is 10kΩ to 300 kΩ. C9 is chosen large compared to C10, typically 0.1 µF, see Figure 4 and Figure 8. 6V to 24V IN VIN LM34919B D1 C1 1 PF GND C2 1 PF C3 Minimum Off Timer On Timer R1 0.1 PF 28k RON/SD A1 Logic SS C6 0.022 PF B3 VCC C3 C4 0.1 PF VIN BST D3 C5 SW D2 0.022 PF L1 8.2 PH ISEN C1 D1 7.87 k: 3300 C9 pF 0.1 PF R5 R6 0: 3.3V VO C10 2.5V FB A3 Regulation Comparator A2 Current Limit Detect RTN R2 787: R4 0: C7 SGND R3 2.49k B1 C8 10 PF 10 PF GN Figure 4. Minimum Output Ripple Configuration 6 Monitor The Inductor Current The inductor’s current can be monitored or viewed on a scope with a current probe. Remove R6, and install an appropriate current loop across the two large pads where R6 was located. In this way, the inductor’s ripple current and peak current can be accurately determined. 7 Scope Probe Adapters Scope probe adapters are provided on this evaluation board for monitoring the waveform at the SW pin, and at the circuit’s output (VOUT), without using the probe’s ground lead that can pick up noise from the switching waveforms.. 8 Minimum Load Current The LM34919B requires a minimum load current of ≊1 mA to ensure the boost capacitor (C5) is recharged sufficiently during each off-time. In this evaluation board, the minimum load current is provided by the feedback resistors allowing the board’s minimum load current at VOUT to be specified at zero. SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated 5 Minimum Load Current www.ti.com C1 1 PF VIN LM34919B D1 C2 1 PF C3 GND Minimum Off Timer On Timer R1 0.1 PF 28k VCC C3 VIN BST D3 0.022 PF SW D2 RON/SD A1 Logic SS C6 0.022 PF B3 C4 0.1 PF SW C5 L1 8.2 PH R6 0: 3.3V VOUT C10 R5 2.5V FB A3 Regulation Comparator A2 Current Limit Detect ISEN C1 D1 R2 787: C9 C7 SGND R3 2.49k B1 RTN R4 0.27: OUTPUT 6V to 24V IN C8 10 PF 10 PF GND Figure 5. Complete Evaluation Board Schematic Table 1. Bill of Materials (BOM) 6 Item Description Mfg., Part Number Package Value C1 Ceramic Capacitor TDK C3216X7R1H105M 1206 1.0 µF, 50V C2 Ceramic Capacitor TDK C3216X7R1H105M 1206 1.0 µF, 50V C3 Ceramic Capacitor TDK C1608X7R1H104K 0603 0.1 µF, 50V C4 Ceramic Capacitor TDK C1608X7R1H104K 0603 0.1 µF, 50V C5 Ceramic Capacitor TDK C1608X7R1H223K 0603 0.022 µF, 50V C6 Ceramic Capacitor TDK C1608X7R1H223K 0603 0.022 µF, 50V C7, C8 Ceramic Capacitor TDK C3216X7R1C106K 1206 10 µF, 16V C9 Ceramic Capacitor Unpopulated 0603 C10 Ceramic Capacitor Unpopulated 0603 D1 Schottky Diode Zetex ZLLS2000 SOT23-6 40V, 2.2A L1 Power Inductor Bussman DR74-8R2–R 7.6 mm x 7.6 mm 8.2 µH, 2.5A R1 Resistor Vishay CRCW060328KOFK 0603 28 kΩ R2 Resistor Vishay CRCW0603787RFK 0603 787 Ω R3 Resistor Vishay CRCW06032K49FK 0603 2.49 kΩ R4 Resistor Panasonic ERJ3RQFR27 0603 0.27Ω R5 Resistor Unpopulated 0603 R6 Resistor Vishay CRCW08050000Z 0805 U1 Switching Regulator LM34919 10 Bump DSBGA AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated 0Ω Jumper SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback Circuit Performance www.ti.com 9 Circuit Performance Figure 6. Efficiency vs Load Current Figure 7. Efficiency vs Input Voltage Figure 8. Output Voltage Ripple Figure 9. Switching Frequency vs. Input Voltage SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated 7 Circuit Performance www.ti.com Figure 10. Load Current Limit vs Input Voltage 8 AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback Typical Waveforms www.ti.com 10 Typical Waveforms Trace 2= VOUT Trace 4= inductor Current Trace 1= SW Pin VIN = 24V, IOUT = 400 mA Figure 11. Continuous Conduction Mode Trace 2= VOUT Trace 4= inductor Current Trace 1= SW Pin VIN = 24V, IOUT = 20 mA Figure 12. Discontinuous Conduction Mode SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated 9 PC Board Layout 11 www.ti.com PC Board Layout Figure 13. Board Silkscreen Figure 14. Board Top Layer 10 AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback PC Board Layout www.ti.com Figure 15. Board Bottom Layer (Viewed from Top) SNVA418A – May 2010 – Revised April 2013 Submit Documentation Feedback AN-2016 LM34919B Evaluation Board Copyright © 2010–2013, Texas Instruments Incorporated 11 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily performed. TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI. Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components in safety-critical applications. In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and requirements. Nonetheless, such components are subject to these terms. No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties have executed a special agreement specifically governing such use. Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and regulatory requirements in connection with such use. TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of non-designated products, TI will not be responsible for any failure to meet ISO/TS16949. Products Applications Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers DLP® Products www.dlp.com Consumer Electronics www.ti.com/consumer-apps DSP dsp.ti.com Energy and Lighting www.ti.com/energy Clocks and Timers www.ti.com/clocks Industrial www.ti.com/industrial Interface interface.ti.com Medical www.ti.com/medical Logic logic.ti.com Security www.ti.com/security Power Mgmt power.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video RFID www.ti-rfid.com OMAP Applications Processors www.ti.com/omap TI E2E Community e2e.ti.com Wireless Connectivity www.ti.com/wirelessconnectivity Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265 Copyright © 2013, Texas Instruments Incorporated