MIC28511 Evaluation Board 60V/3A Synchronous Buck Regulator General Description Requirements Micrel’s MIC28511 is a synchronous step-down regulator featuring unique adaptive on-time control architecture with integrated power MOSFETs. The MIC28511 operates over an input supply range of 4.6V to 60V, and can be used to supply up to 3A of output current. The output voltage is adjustable down to 0.8V with a guaranteed accuracy of ±1% from 0°C to 85°C. The device operates with a programmable switching frequency from 200kHz to 680kHz (nominal). The MIC28511 evaluation board requires only a single power supply with at least 5A current capability. For applications where VIN is less than +5.5V the internal LDO can be bypassed by tying VDD to VIN. ® The MIC28511-1 uses the HyperLight Load architecture to operate in pulse-skipping mode at light load while functioning in fixed-frequency CCM mode from medium load to heavy load. The MIC28511-2 utilizes Hyper Speed TM Control architecture, operating in fixed-frequency CCM mode under all load conditions. Datasheets and support documentation are available on Micrel’s web site at: www.micrel.com. Precautions The MIC28511 evaluation board does not have reverse polarity protection. Applying a negative voltage to the VIN and GND terminals can damage the device. The maximum VIN of the board is rated at 60V; exceeding 60V can damage the device. Ordering Information Part Number MIC28511-1YML EV MIC28511-2YML EV Description MIC28511 Evaluation Board Evaluation Board Hyper Speed Control is a trademark and HyperLight Load is a registered trademark of Micrel, Inc. Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com April 9, 2015 Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board Where: Getting Started VREF = 0.8V, and R1 is 10.0kΩ. 1. Connect VIN Supply Connect a supply to the VIN and GND terminals, paying careful attention to the polarity and the supply range (4.6V < VIN < 60V). Monitor IIN with a current meter and monitor input voltage at VIN and GND terminals with a voltmeter. Do not apply power until Step 4. With jumpers J11, J8, and J7 removed, the output regulates at the 0.8V reference voltage. All other voltages not listed can be set by modifying the R9 with Jumper J7 installed according to Equation 2: R9 = 2. Connect Load and Monitor Input Connect a load to the VOUT and GND terminals. The load can be either a passive or an active electronic load. A current meter can be placed between the VOUT terminal and load to monitor the output current. Ensure the output voltage is monitored at the VOUT terminal. R1× VREF VOUT - VREF Eq. 2 Jumper J12 shorts out the feedback and forces the converter to operate open loop and approach 100% duty cycle. SW Node Use test point J1 (VSW) for monitoring the power MOSFET switching waveform. 3. Enable Input The EN terminal has an on board 100kΩ pull-up resistor (R16) to VIN, which allows the output to be turned on when PVDD exceeds its UVLO threshold. An EN (J16) connector is provided on the evaluation board for ease-of-access to the enable feature. Applying an external logic signal on the EN terminal to pull it low or using a jumper to short the EN terminal to the GND terminal will disable the MIC28511 evaluation board. Current Limit The MIC28511 uses the RDS(ON) and external resistor connected from ILIM to the SW node to decide the current limit (see Figure 1). 4. Apply Power Apply VIN and verify that the output voltage regulates to the set voltage. Evaluation Board Description The basic parameters of the evaluation board are: • Input range: 4.6V to 60V • Output range: 0.8V to 0.85V × VIN at 3A. (For more detailed information, refer to Typical Characteristics section. Note that 0.85V is the maximum duty cycle of the MIC28511 controller) Figure 1. MIC28511 Current Limiting Circuit In each switching cycle of the MIC28511 converter, the inductor current is sensed by monitoring the low-side MOSFET in the OFF period. The sensed voltage V(ILIM) is compared with the power ground (PGND) after a blanking time of 150ns. In this way, the drop voltage over the resistor R22 (VCL) is compared with the drop over the bottom FET generating the short current limit. The small capacitor (C18) connected from ILIM pin to PGND filters the switching node ringing during the off time which allows a better short-limit measurement. The time constant created by R22 and C18 should be much less than the minimum off time. • 300kHz switching frequency (Adjustable 200kHz to 680kHz) Feedback Resistors With Jumper J11 in place, the output voltage is set to 5.0V as determined by the feedback dividers R1 and R11. Jumper J8 sets the output voltage to 3.3V. With jumper J7 in place the output is set by modifying R9, as illustrated in Equation 1: R1 VOUT = VREF × 1 + R9 April 9, 2015 The VCL drop allows programming of short limit through the value of the resistor (R22). If the absolute value of the voltage drop on the bottom FET is greater than VCL, V(ILIM) is lower than PGND and a short-circuit event is triggered. Eq. 1 2 Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board A “hiccup” soft-start cycle is generated, reducing the stress on the power switching FETs while protecting the load and supply during severe short conditions. The MIC28511 evaluation board was designed with a 6.8µH inductor for operation at 300kHz at 5V output. The typical value of RWINDING(DCR) of this particular inductor is 39mΩ. The short circuit current limit can be programmed by using Equation 3: R 22 = (ICLIM - ΔIL (PP) × 0.5) × R DS(ON) + VCL Setting the Switching Frequency The MIC28511 switching frequency can be adjusted by changing the value of resistor R17. The top resistor (R19) is set at 100kΩ and is connected between VIN and FREQ. R17 is connected from the FREQ input to PGND and sets the switching frequency according to Equation 4. Eq. 3 ICL Where: ICLIM = Desired current limit RDS(ON) = On-resistance of low-side power MOSFET, 28mΩ typically VCL = Current-limit threshold (typical absolute value is 14mV, per the Electrical Characteristics section in the MIC28511 datasheet) ICL = Current-limit source current (typical value is 70µA, per the Electrical Characteristics section in the MIC28511 datasheet). Figure 2. Switching Frequency Adjustment ΔIL(PP) = Inductor current peak-to-peak fSW _ ADJ = fO × The peak-to-peak inductor current ripple is: ∆IL(PP) = VOUT × (VIN(MAX) - VOUT ) VIN(MAX) × fsw × L R17 R19 + R17 Eq. 4 Where: Eq. 4 fO = Switching frequency when R17 is open, per the Electrical Characteristics section in the MIC28511 datasheet. In case of hard short, the short current-limit threshold (VCL) is reduced by half to the short-circuit threshold. This allows an indefinite hard short on the output without any destructive effect. It is critical to make sure that the inductor current used to charge the output capacitance during soft start is below the foldback short-circuit level; otherwise the supply may go into hiccup mode and latch up at start up. This should be verified over the operating temperature range as well. For a more precise setting, it is recommended to use the Figure 3: The MOSFET RDS(ON) varies 30% to 40% with temperature. Therefore, it is recommended to add a 50% margin to ICL in Equation 4 to avoid false current limiting due to increased MOSFET junction temperature rise. Table 1 shows typical output current limit value for a given R22. Table 1. R22 Typical Output Current-Limit Value R22 Typical Output Current Limit (VIN = 12V, VOUT = 5V, L = 6.8µH) 1.74kΩ 4.4 A 1.24kΩ 3.1 A April 9, 2015 Figure 3. Switching Frequency vs. R17 3 Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board Typical Characteristics 100 100 90 90 5.0V 90 80 3.3V 80 70 3.3V 60 2.5V EFFICIENCY (%) 5.0V 50 40 100 5.0V EFFICIENCY (%) 80 EFFICIENCY (%) Efficiency (VIN = 48V) vs. Output Current MIC28511-1 Efficiency (VIN = 24V) vs. Output Current MIC28511-1 Efficiency (VIN =12V) vs. Output Current MIC28511-1 2.5V 70 60 50 40 20 20 fSW = 300kHz 10 0.01 0.1 1 50 40 0.1 1 fSW = 300kHz 20 fSW = 300kHz 10 0.01 10 2.5V 60 30 30 30 3.3V 70 10 0.01 10 0.1 OUTPUT CURRENT (A) OUTPUT CURRENT (A) 24V Input Thermal Derating MIC28511-1 12V Input Thermal Derating MIC28511-1 3.5 1 10 OUTPUT CURRENT (A) 48V Input Thermal Derating MIC28511-1 3.5 3.5 3.0 3.0 OUTPUT CURRENT (A) 5.0V 3.3V 2.5 2.0 1.5 VIN =12V fSW = 300kHz TJMAX =125°C θJA = 30°C/W 1.0 0.5 5.0V 3.3V 2.5V 2.5 2.0 1.5 VIN =24V fSW = 300kHz TJMAX =125°C θJA = 30°C/W 1.0 0.5 0.0 40 55 70 85 25 100 IC Power Dissipation vs. Output Current MIC28511-1 IC POWER DISSIPATION (W) IC POWER DISSIPATION (W) 40 55 70 85 0.8 0.6 5.0V 3.3V 0.2 25 1 1.5 2 OUTPUT CURRENT (A) April 9, 2015 2.5 3 55 70 85 100 IC Power Dissipation vs. Output Current MIC28511-1 3.0 1.5 1.0 5.0V 0.5 3.3V 2.5V 0.0 0.0 40 AMBIENT TEMPERATURE (°C) VIN ==24V Vin 24V fSW = 300kHz 2.5V 0.5 VIN = 48V fSW = 300kHz TJMAX = 125°C θJA = 30°C/W 1.0 100 2.0 VIN = 12V fSW = 300kHz 0 1.5 IC Power Dissipation vs. Output Current MIC28511-1 1.2 0.4 2.0 AMBIENT TEMPERATURE (°C) AMBIENT TEMPERATURE (°C) 1.0 5.0V 2.5 0.0 0.0 25 3.3V 2.5V 0.5 IC POWER DISSIPATION (W) OUTPUT CURRENT (A) 3.0 OUTPUT CURRENT (A) 2.5V VIN ==24V Vin 48V fSW = 300kHz 2.5 2.0 1.5 5.0V 3.3V 1.0 2.5V 0.5 0.0 0 0.5 1 1.5 2 OUTPUT CURRENT (A) 4 2.5 3 0 0.5 1 1.5 2 2.5 3 OUTPUT CURRENT (A) Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board Typical Characteristics (Continued) 100 90 90 90 80 80 80 5.0V 3.3V 2.5V 70 60 50 40 70 5.0V 3.3V 2.5V 60 50 40 fSW = 300kHz 0.1 1 fSW = 300kHz 20 10 0.01 10 0.1 12V Input Thermal Derating MIC28511-2 OUTPUT CURRENT (A) 10 0.01 10 1.5 VIN = 12V fSW = 300kHz TJMAX =125°C θJA = 30°C/W 55 70 3.0 2.5 3.3V 2.0 1.5 2.5V VIN = 24V fSW = 300kHz TJMAX =125°C θJA = 30°C/W 1.0 85 40 2.0 1.5 VIN = 48V fSW = 300kHz TJMAX = 125°C θJA = 30°C/W 1.0 0.5 55 70 85 25 100 IC POWER DISSIPATION (W) 1.2 1.0 0.8 5.0V 3.3V 70 85 100 3.0 VIN ==24V Vin 24V fSW = 300kHz 1.5 1.0 5.0V 0.5 55 IC Power Dissipation vs. Output Current MIC28511-2 2.0 VIN =12V fSW = 300kHz 40 AMBIENT TEMPERATURE (°C) IC Power Dissipation vs. Output Current MIC28511-2 1.8 0.6 2.5 AMBIENT TEMPERATURE (°C) IC Power Dissipation vs. Output Current MIC28511-2 1.4 5.0V 3.3V 2.5V 3.0 0.0 25 100 AMBIENT TEMPERATURE (°C) 1.6 10 48V Input Thermal Derating MIC28511-2 0.0 40 1 3.5 0.5 0.0 25 0.1 OUTPUT CURRENT (A) IC POWER DISSIPATION (W) OUTPUT CURRENT (A) 2.5V 0.5 fSW = 300kHz 5.0V 3.3V 1.0 1 3.5 3.0 2.0 40 24V Input Thermal Derating MIC28511-2 5.0V 2.5 50 OUTPUT CURRENT (A) OUTPUT CURRENT (A) 3.5 5.0V 3.3V 2.5V 60 20 OUTPUT CURRENT (A) 10 0.01 70 30 30 20 0.4 EFFICIENCY (%) 100 EFFICIENCY (%) EFFICIENCY (%) 100 30 IC POWER DISSIPATION (W) Efficiency (VIN = 48V) vs. Output Current MIC28511-2 Efficiency (VIN = 24V) vs. Output Current MIC28511-2 Efficiency (VIN = 12V) vs. Output Current MIC28511-2 3.3V 2.5V 0.2 VIN = 48V fSW = 300kHz 2.5 2.0 1.5 5.0V 1.0 3.3V 2.5V 0.5 2.5V 0.0 0.0 0.0 0.0 0.5 1.0 1.5 2.0 OUTPUT CURRENT (A) April 9, 2015 2.5 3.0 0.0 0.5 1.0 1.5 2.0 OUTPUT CURRENT (A) 5 2.5 3.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 OUTPUT CURRENT (A) Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board Evaluation Board Schematic Bill of Materials Item C1 C2, C3 C4, C7 Part Number UVZ2A330MPD 12061Z475KAT2A C1608X7R1A225K080AC Manufacturer Description (1) Nichicon 33µF/100V 20% Radial Aluminum Capacitor 1 (2) 4.7µF/100V, X7S, Size 1206 Ceramic Capacitor 2 (3) 2.2µF/10V, X7R, Size 0603 Ceramic Capacitor 2 Open NA 0.1µF/10V, X7R, Size 0603 Ceramic Capacitor 2 0.47µF/100V, X7R, Size 0805 Ceramic Capacitor 1 Murata 0.1µF/100V, X7R, Size 0603 Ceramic Capacitor 2 TDK 470pF/50V, X7R, Size 0603 Ceramic Capacitor 1 AVX TDK C5, C11, C13, C18, C19, C20 C6, C16 C9 C0603C104K8RACTU GRM21BR72A474KA73 08051C474KAT2A C10, C17 GRM188R72A104KA35D C12 CGA3E2X7R1H471K Qty. (4) Kemet Murata (5) AVX Notes: 1. Nichicon: www.nichicon.co.jp/english. 2. AVX: www.avx.com. 3. TDK: www.tdk.com. 4. Kemet.: www.kemet.com. 5. Murata: www.murata.com. April 9, 2015 6 Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board Bill of Materials (Continued) Item Part Number C14, C15 GRM32ER71A476KE15L Murata C21 C1608NP02A270J080AA TDK D1 BAT46W-TP Manufacturer (6) MCC D3 77311-118-02LF L1 XAL7030-682MED CRCW060310K0FKEA FCI (7) Coilcraft (8) Vishay Dale (9) R2, R9, R25, R26 Qty. 47µF/10V, X7R, Size 1210 Ceramic Capacitor 2 27pF 100V, NPO, Size 0603 Ceramic Capacitor 1 100V Small Signal Schottky Diode, SOD123 1 Open J1, J7, J8, J10 − J12, J16 − J18 R1 Description NA CONN HEADER 2POS VERT T/H 9 6.8µH, 10.7A Saturation Current 1 10.0kΩ, Size 0603, 1% Resistor 1 Open NA R10 CRCW06033K24FKEA Vishay Dale 3.24kΩ, Size 0603, 1% Resistor 1 R11 CRCW06031K91FKEA Vishay Dale 1.91kΩ, Size 0603, 1% Resistor 1 R14, R15 CRCW06030000FKEA Vishay Dale 0.0 Ω, Size 0603, Resistor Jumper 2 R3, R16, R17, R19 CRCW0603100K0FKEA Vishay Dale 100kΩ, Size 0603, 1% Resistor 4 R18 CRCW06031K00JNEA Vishay Dale 1.0kΩ, Size 0603, 5% Resistor 1 R20, R21 CRCW060349R9FKEA Vishay Dale 49.9Ω, Size 0603, 1% Resistor 2 R22 CRCW06031K74FKEA Vishay Dale 1.74kΩ, Size 0603, 1% Resistor 1 R23 CRCW08051R21FKEA Vishay Dale 1.21Ω, Size 0805, 1% Resistor 1 R24 CRCW060310R0FKEA Vishay Dale 10.0Ω, Size 0603, 1% Resistor 1 TP7, TP14, TP8, TP13, TP17, TP18 TP9 − TP12 U1 Open 1502 MIC28511-1YFL MIC28511-2YFL Keystone (10) Electronics (11) Micrel. Inc. NA Test Point Turret, .090 4 60V/3A Synchronous Buck Regulator 1 Notes: 6. MCC: www.mcc.com. 7. FCI: www.fciconnect.com. 8. Coilcraft: www.coilcraft.com. 9. Vishay Dale: www.vishay.com. 10. Keystone Electronics: www.keystone.com. 11. Micrel, Inc.: www.micrel.com. April 9, 2015 7 Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board Evaluation Board Layout Recommendations Top Layer Mid-Layer 1 (Ground Plane) April 9, 2015 8 Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board Evaluation Board Layout Recommendations (Continued) Mid-Layer 2 Bottom Layer April 9, 2015 9 Revision 1.0 Micrel, Inc. MIC28511 Evaluation Board MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com Micrel, Inc. is a leading global manufacturer of IC solutions for the worldwide high-performance linear and power, LAN, and timing & communications markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products. Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and advanced technology design centers situated throughout the Americas, Europe, and Asia. Additionally, the Company maintains an extensive network of distributors and reps worldwide. Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2015 Micrel, Incorporated. April 9, 2015 10 Revision 1.0