LM25010EVAL

User's Guide SNVA142A – December 2005 – Revised April 2013 AN-1431 LM25010 Evaluation Board 1 Introduction The LM25010EVAL 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 5 V output over an input range of 6 V - 42 V. The circuit delivers load currents to 1A, with current limit set at ≊1.3A. The board is populated with all external components except R6 and C9-C11. These components provide options for reducing output ripple as described later in this document. The board’s specification are: • Input Voltage: 6 V to 42 V • Output Voltage: 5 V • Maximum load current: 1.0A • Minimum load current: 0A • Current Limit: 1.3A • Measured Efficiency: 95.5% (VIN = 6 V, IOUT = 200 mA) • Nominal Switching Frequency: 200 kHz • Size: 2.25 in. x 0.88 in. x 0.47 in C9 C10 C8 J3 LM25010 BUCK EVALUATION L1 C7 BOARD NATIONAL C2005 P/N 55101 2722-001 SEMICONDUCTOR OUT1 U1 C6 C3 OUT2 D1 S/N R4 R1 IN GND R5 R6 R3 C11 C2 R2 C5 C1 C4 REV A GND J1 Figure 1. Evaluation Board - Top Side 2 Theory of Operation Figure 3 contains a simplified block diagram of the LM25010. When the circuit is in regulation, the buck switch is on each cycle for a time determined by R1 and VIN according to the equation: tON = 1.18 x 10-10 x (R1 + 1.4k) (VIN - 1.4V) + 67 ns (1) All trademarks are the property of their respective owners. SNVA142A – December 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated AN-1431 LM25010 Evaluation Board 1 Board Layout and Probing www.ti.com The on-time of this evaluation board ranges from ≊5000 ns at VIN = 6 V, to ≊650 ns at VIN = 42 V. The ontime varies inversely with VIN to maintain a nearly constant switching frequency. At the end of each ontime the Minimum Off-Timer ensures the buck switch is off for at least 260 ns. In normal operation, the offtime is much longer. During the off-time, the output capacitor (C7) is discharged by the load current. When the output voltage falls sufficiently that the voltage at FB is below 2.5 V, the regulation comparator initiates a new on-time period. For stable, fixed frequency operation, ≊25 mV of ripple is required at FB to switch the regulation comparator. For a more detailed block diagram and a complete description of the various functional blocks, see the LM25010/LM25010Q 42V, 1.0A Step-Down Switching Regulator Data Sheet (SNVS419). 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: 1) When operating at high input voltage and high load current, forced air flow is necessary. 2) The LM25010, and the diode D1 will be hot to the touch when operating at high input voltage and high load current. 3) Use CAUTION when probing the circuit at high input voltages to prevent injury, as well as possible damage to the circuit. 4) At maximum load current (1A), 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 normally connected to the OUT1 and GND terminals of the J3 connector. 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 6 V, at which time the output voltage should be 5 V. If the output voltage is correct with 6 V at VIN, then increase the input voltage as desired and proceed with evaluating the circuit. 5 Reducing Output Ripple The LM25010 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. In the basic application circuit shown in the data sheet, C8 is not included. The required ripple at FB is derived from the ripple at VOUT1, which is generated by the inductor’s ripple current passing through R4 and the ESR of capacitor C7. Since the ripple voltage at VOUT1 is attenuated by the R2/R3 feedback divider, a minimum of 50 mVp-p is required at VOUT1. If this ripple level is acceptable for the intended application, C8 can be removed from this evaluation board, and R4 increased to 1.5Ω. In that case, the minimum ripple amplitude (≊55 mVp-p) occurs at minimum Vin (6 V), and increases to ≊300 mVp-p at Vin = 42 V, as shown in Figure 6. If a low ripple output is desired three alternatives are described below. A) Ripple Reduction Option A: This EVB is supplied with C8 installed, and R4 = 0.68Ω, providing a relatively low ripple output at VOUT1 since C8 couples the output ripple directly to FB without attenuation. The ripple amplitude at VOUT1 ranges from 30mVp-p to 150 mVp-p (see Figure 6) as VIN is varied over its range. The minimum value for C8 is calculated from: C8 = tON(max) (R2//R3) (2) where tON(max) is the maximum on-time at minimum VIN, and R2//R3 is the equivalent parallel value of R2 and R3. For this evaluation board, tON(max) is approximately 5000 ns, and R2//R3 = 2.5kΩ, resulting in a minimum value of 0.002 µF for C8. 2 AN-1431 LM25010 Evaluation Board SNVA142A – December 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated Increasing the Current Limit www.ti.com B) Ripple Reduction Option B: Add R6, C9, C10, replace R4 with zero ohms, and leave C8 and C11 positions open. Since the SW pin switches from -1 V to VIN, and the right end of C9 is a virtual ground, R6 and C9 are chosen to generate a 30-40 mVp-p triangle wave at their junction. That triangle wave is coupled to the FB pin through C10. To calculate the values for R6, C9, and C10, use the following procedure, using the minimum input voltage for VIN: 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 1 V), and Vin is the minimum input voltage. For this circuit, VA calculates to 4.83 V. This is the DC voltage at the R6/C9 junction, and is used in the next equation. Calculate the R6•C9 product: R6 ‡ C9 = (Vin - VA) x tON 'V (4) where tON is the on-time at minimum VIN (≊5 µs), and ΔV is the desired ripple amplitude at the R6/C9 junction, 30 mV for this example. R6 · C9 = (6V - 4.83V ) ´ 5μs = 1.95 ´ 104 0.03V (5) R6 and C9 are then chosen from standard value components to satisfy the above product. For example, C9 can be 1000 pF, requiring R6 to be 195 kΩ. C10 is chosen to be 0.01 µF, large compared to C9. The resulting circuit is: BST 3 LM25010 0.022 PF L1 C6 100 PH SW 5V 2 D1 ISEN 4 R6 195k C10 0.01 PF C9 1000 pF VOUT1 R2 5k FB 9 6 RTN SGND 5 R3 5k R4 0 C7 22 PF Gnd Figure 2. Low Ripple Output Using R6, C9, C10 The resulting ripple at VOUT1 ranges from 3 mVp-p at VIN = 6 V, to 11 mVp-p at VIN = 42 V, and varies slightly with load current (see Figure 6). These values are valid only for continuous conduction mode (load current is between 120 mA and 1.3A). If the load current is reduced below 120 mA such that the circuit operates in discontinuous conduction mode the VOUT1 ripple ranges from ≊40 mVp-p to ≊120 mVp-p. If the circuit is operated in current limit mode the ripple ranges from ≊100 mVp-p to ≊300 mVp-p. B) Ripple Reduction Option C: Connect the load to VOUT2 (leave R4 in). The ripple at this output varies from ≊3 mVp-p to ≊10 mVp-p over the input voltage range (see Figure 6). However, the load regulation is not as good at VOUT2 as at VOUT1 due to the presence of R4. This alternative may be preferred for applications where the load current is relatively constant. 6 Increasing the Current Limit The evaluation board current limit activates at a load current of ≊1.3A. If it is desired to increase the current limit for a particular application, R5 must be added to the board. To determine the appropriate value for this resistor, see the LM25010/LM25010Q 42V, 1.0A Step-Down Switching Regulator Data Sheet (SNVS419). SNVA142A – December 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated AN-1431 LM25010 Evaluation Board 3 Minimum Load Current 7 www.ti.com Minimum Load Current The LM25010 requires a minimum load current of ≊500 µA to ensure the boost capacitor (C6) is recharged sufficiently during each off-time. In this evaluation board, the minimum load current is provided by the feedback resistor (R2, R3), allowing the board’s minimum load current at VOUT1 (or VOUT2) to be specified at zero. 6V ± 42V VIN 13 C3 Vin C1 2.2 PF C2 2.2 PF LM25010 Minimum Off Timer On Timer R1 200k 0.1 PF VCC 12 VIN Gnd C5 0.022 PF RON/SD 11 SS 10 FB 9 C4 0. 47 PF BST 3 C6 0.022 PF L1 100 PH SW 2 Logic 2.5V 5V D1 R6 ISEN 4 R5 Regulation Comparator 6 RTN SGND 5 VOUT1 C9 C10 C8 001 . PF C11 R2 5k R4 0.68 VOUT2 R3 5k C7 22 PF Gnd Figure 3. Evaluation Board Schematic Table 1. Bill of Materials Item Description Mfg., Part Number Package Value C1, 2 Ceramic Capacitor TDK C3225X7R1H225M 1210 2.2 µF, 50 V C3 Ceramic Capacitor TDK C2012X7R2A104M 0805 0.1 µF, 100 V C4 Ceramic Capacitor TDK C2012X7R1C474M 0805 0.47 µF, 16 V C5, 6 Ceramic Capacitor TDK C2012X7R1C223M 0805 0.022 µF, 16 V C7 Ceramic Capacitor TDK C3225X7R1C226M 1210 22 µF, 16 V C8 Ceramic Capacitor TDK C2012X7R1C103M 0805 0.01 µF, 16 V C9 Unpopulated C10 Unpopulated C11 Unpopulated D1 Schottky Diode Central Semi DFLS160 Power DI123 60 V,1A L1 Power Inductor TDK SLF12575T-101M1R9, or 12.5 mm x 12.5 mm 100 µH, 1.9A Cooper Bussmann DR125-101 R1 Resistor CRCW08052003F 0805 200 kΩ R2, 3 Resistor CRCW08054991F 0805 4.99 kΩ R4 Resistor ERJ-6RQFR68V (Panasonic) 0805 0.68 Ω R5 Unpopulated R6 U1 4 Unpopulated Switching Regulator AN-1431 LM25010 Evaluation Board LM25010 TSSOP - 14EP SNVA142A – December 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated Minimum Load Current www.ti.com 100 VIN = 6V EFFICIENCY (%) 90 80 10V 70 20V 30V 60 42V 50 0 50 200 400 600 800 1000 LOAD CURRENT (mA) Figure 4. Efficiency vs Load Current 100 Load Current = 200 mA EFFICIENCY (%) 90 Load Current = 1000 mA 80 Load Current = 50 mA 70 60 50 6 12 18 24 30 36 42 VIN (V) Figure 5. Efficiency vs VIN 1000 OUTPUT RIPPLE (mVp-p) R6, C8-C11 Not Installed R4 = 1.5: 100 C8 = 0.01 PF, R4 = 0.68: R6, C9, C10 Installed, R4 = 0 10 VOUT2 Load Current = 200 mA 1 6 12 18 24 30 36 42 VIN (V) Figure 6. Voltage Ripple at VOUT1, VOUT2 SNVA142A – December 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated AN-1431 LM25010 Evaluation Board 5 PCB Layout 8 www.ti.com PCB Layout Figure 7. Board Silkscreen Figure 8. Board Top Layer Figure 9. Board Bottom Layer (viewed from top) 6 AN-1431 LM25010 Evaluation Board SNVA142A – December 2005 – Revised April 2013 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated 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