SM3320-BATT-EV/NOPB

Application Report SNOSB76C – December 2010 – Revised May 2013 AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design ..................................................................................................................................................... ABSTRACT The SM72442 MPPT digital controller and SM72295 photovoltaic full bridge drivers are designed to control high-efficiency DC/DC conversion used in photovoltaic applications. This application report details the usage of those devices in a battery charging application. The reference design is meant to provide support for a wide variety of implementations, however, unless otherwise noted, this reference design system is shown charging a 12V commercial automotive lead acid battery. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Contents Charging Profile ............................................................................................................. 3 Features ...................................................................................................................... 3 Quick Setup Procedure .................................................................................................... 4 10V Power Supply .......................................................................................................... 4 DC/DC Converter ........................................................................................................... 5 Programmable Modes/Gain Settings ..................................................................................... 6 Current Sense Gains and Offset .......................................................................................... 6 Start-Up Circuitry ............................................................................................................ 7 Output FET Disabling ....................................................................................................... 8 Output Current Regulation ................................................................................................. 9 Voltage Regulation .......................................................................................................... 9 MPPT ....................................................................................................................... 10 Microcontroller Functions ................................................................................................. 11 13.1 Normal Operation ................................................................................................. 11 13.2 Start-Up Operation ............................................................................................... 11 13.3 Safety Feature .................................................................................................... 11 Microcontroller Program Code ........................................................................................... 13 14.1 Function: check_lead_acid() .................................................................................... 14 14.2 Function: Main() .................................................................................................. 14 14.3 Function: get_i2c_data ........................................................................................... 14 14.4 Function: send_i2c_command(char number) ................................................................. 15 14.5 Function: Set_Voutmax() ........................................................................................ 15 14.6 Function: Check_low_current() ................................................................................. 15 Charging a Li-ion Battery ................................................................................................. 15 Bill of Materials ............................................................................................................. 17 Charge Controller System Schematic .................................................................................. 19 List of Figures 1 Lead-Acid Charging Profile ................................................................................................ 3 2 System Connection ......................................................................................................... 4 3 10V Power Supply .......................................................................................................... 4 4 DC/DC Converter Stage 5 ................................................................................................... Buck Gate Drive Signals From SM72442................................................................................ 5 5 SolarMagic is a trademark of Texas Instruments. All other trademarks are the property of their respective owners. SNOSB76C – December 2010 – Revised May 2013 Submit Documentation Feedback AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design Copyright © 2010–2013, Texas Instruments Incorporated 1 www.ti.com 6 Switch Nodes in Buck Mode ............................................................................................... 5 7 Boost Gate Drive Signals From SM72442 ............................................................................... 6 8 Switch Nodes in Boost Mode .............................................................................................. 6 9 Start-Up Boost Circuitry .................................................................................................... 7 10 Start-up Circuit Timing Diagram........................................................................................... 8 11 Start-up VPanel < VBatt ......................................................................................................... 8 12 Start-up Detail of Battery Current ......................................................................................... 8 13 Charging Waveforms During Float 14 Battery Charging with VPanel < VBattery (Boost) 15 16 17 18 19 20 21 2 ....................................................................................... 9 ........................................................................... 10 Battery Charging with VPanel > VBattery (Buck) ............................................................................ 10 Basic Operational Flowchart ............................................................................................. 12 Microcontroller Code Flowchart.......................................................................................... 13 Microcontroller Code Block Diagram .................................................................................... 15 Li-ion Charge Profile ...................................................................................................... 16 Charge Controller System Schematic, Part 1.......................................................................... 19 Charge Controller System Schematic, Part 2.......................................................................... 20 AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design SNOSB76C – December 2010 – Revised May 2013 Submit Documentation Feedback Copyright © 2010–2013, Texas Instruments Incorporated Charging Profile www.ti.com 1 Charging Profile Figure 1 shows the lead-acid charging profile used in this reference design. If the battery voltage is very low, a slow charge current is applied and limited until the voltage rises above a pre-set threshold value Vt. The full charge current is then applied. Once full charge is detected on the voltage of the battery, the system switches to a floating charge and maintains the battery voltage at a fixed threshold. At any time, the system will run in MPPT mode if the available power is lower than the power required to achieve voltage or current regulation. Figure 1. Lead-Acid Charging Profile 2 Features • • • • • • • • • • 12V Lead Acid Battery Vin range = 15V to 45V Vmp (50V Voc) Max Input Current: Isc = 11A MPPT algorithm for optimized photovoltaic applications Up to 9A charging current Reverse current protection Trickle charge and fast charge mode Up to 98% converter efficiency 14.2V max charge voltage, 13.5V floating voltage Output voltage set-points can be re programmed SNOSB76C – December 2010 – Revised May 2013 Submit Documentation Feedback AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design Copyright © 2010–2013, Texas Instruments Incorporated 3 Quick Setup Procedure 3 www.ti.com Quick Setup Procedure Step 1: Verify lead-acid battery voltage less than 12V, higher than 10V. Step 2: Connect battery to output terminals as shown in Figure 2. Step 3: Connect Solar panel or Solar Array Simulator to the input terminals as shown in Figure 2. Step 4: Verify battery charging current up to 9A (Average slightly under 9A). Step 5: If battery current low, verify input operates at maximum power point voltage as specified by the panel manufacturer. Step 6: Verify charging profile follows the profile shown in Figure 1. Figure 2. System Connection 4 10V Power Supply The circuit shown in Figure 3 will provide a 10V power supply rail required to properly bias the SM72295 gate driver. The system can be configured to work with solar panels up to100V (with proper components sizing) and down to 12V Vmp. Figure 3. 10V Power Supply 4 AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design SNOSB76C – December 2010 – Revised May 2013 Submit Documentation Feedback Copyright © 2010–2013, Texas Instruments Incorporated DC/DC Converter www.ti.com 5 DC/DC Converter The DC/DC converter stage is a step up/step down four switch converter as shown in Figure 4. This stage transfers the power from the PV panel to the load. Figure 4. DC/DC Converter Stage C18, R11, and D15 as shown in the system schematic in Figure 20, form a snubber to reduce ripple on the switch node on the “Buck” side of the converter. C19,R14 and D14 form a snubber circuit to reduce ripple on the switch node of the “Boost” side of the converter. When the circuit operates in Buck mode, the Boost switch node will issue small pulses at a lower frequency in order to recharge the Bootstrap capacitor of Q2. Likewise, in Boost mode, the Buck switch node will pulse to recharge the bootstrap capacitor of Q1. Specific design guidelines for the DC/DC converter can be found in the AN-2124 Power Circuit Design for SolarMagic SM3320 Application Report (SNOSB84) for power optimizers. Specific timings related to the switches can be found in SM72442 Programmable Maximum Power Point Tracking Controller for Photovoltaic Solar Panels (SNVS689) and SM72295 Photovoltaic Full Bridge Driver (SNVS688). The waveforms in Figure 5 through Figure 8 are examples of the switching signals of the DC/DC converter stage. If the system is to be used at elevated power levels causing high temperature increases in MOSFETs Q1, Q2, Q3, and/or Q4, we recommend the use of a proper heatsink for the MOSFETs, especially at higher ambient temperatures. Care must be taken to prevent electrical contact between the drains of the MOSFETs in the process of proper heatsinking. Figure 5. Buck Gate Drive Signals From SM72442 SNOSB76C – December 2010 – Revised May 2013 Submit Documentation Feedback Figure 6. Switch Nodes in Buck Mode AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design Copyright © 2010–2013, Texas Instruments Incorporated 5 Programmable Modes/Gain Settings www.ti.com Figure 7. Boost Gate Drive Signals From SM72442 6 Figure 8. Switch Nodes in Boost Mode Programmable Modes/Gain Settings The voltage dividers for the output voltage sensing are set to ensure high resolution of the output voltage while providing a safe voltage ( VBattery (Buck) SNOSB76C – December 2010 – Revised May 2013 Submit Documentation Feedback Copyright © 2010–2013, Texas Instruments Incorporated Microcontroller Functions www.ti.com 13 Microcontroller Functions The charge profile is implemented in the current design using a PIC16F722 microcontroller. 13.1 Normal Operation The flowchart in Figure 16 details the operation of the microcontroller needed to achieve the desired charging pattern. Modification to this flowchart can easily be done and programmed to include: • Modified threshold depending on temperature (if battery temperature information available). • Timer to maintain high voltage threshold for a certain time before switching to floating charge to maximize energy stored in the battery. • Pulse charging during the float charge period. The microcontroller is programmed using a 10 pin CLE-105 connector (J5). The connections are: • 1: NC (Not Connected) • 2: PGD/ICSPDAT • 3: GND • 4: PGC/ICSPCLK • 5: NC • 6: GND • 7: +5Vdc • 8: MCLR! • 9: GND • 10: NC Refer to the Microchip website for proper programming/debugging of the PIC16F family microcontrollers. 13.2 Start-Up Operation At start-up, the microcontroller needs to assess the PV and battery voltage to verify proper connection and values. If the values are within the specified range (correct panel and battery voltage), the microcontroller enables the charge by releasing the RESET line of the SM72442 chip. If needed, the start-up circuit is turned on by setting RB5 to ‘1’ (5V) (If the microcontroller used in the application is running below 5V, a level shifting circuit will be necessary). Once current begins to flow in the battery the start-up circuit can be released. While the start-up circuit is enabled, the panel current and voltage are not available through I2C. The corresponding registers can be read but will not contain the correct values. 13.3 Safety Feature The microcontroller is programmed by default to stop charging the battery if the output voltage is above 14.5V or below 8V. SNOSB76C – December 2010 – Revised May 2013 Submit Documentation Feedback AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design Copyright © 2010–2013, Texas Instruments Incorporated 11 Microcontroller Functions www.ti.com Figure 16. Basic Operational Flowchart 12 AN-2121 SolarMagic™ SM3320-BATT-EV Charge Controller Reference Design SNOSB76C – December 2010 – Revised May 2013 Submit Documentation Feedback Copyright © 2010–2013, Texas Instruments Incorporated Microcontroller Program Code www.ti.com 14 Microcontroller Program Code The flowchart in Figure 17 is representative of the code programmed inside the microcontroller. The check_lead_acid function issues a value depending on the state of the battery as detected by the voltage. The main function uses this value to issue the proper action. The other functions in the program are essentially I2C driver functions and low level port setup functions. Initialization Wait Release SM72442 Reset Engage SM72442 Reset Set SM72442 Output Voltage to 14.3V Yes Vbatt>14.5V? Defective battery or no batter No Vbatt14.2V? Yes Set voltage to 13.5V Yes Set low current limit No Vbatt