SM72441 SM72441 Programmable Maximum Power Point Tracking Controller for Photovoltaic Solar Panels Literature Number: SNOSB64F SM72441 Programmable Maximum Power Point Tracking Controller for Photovoltaic Solar Panels General Description Features The SM72441 is a programmable MPPT controller capable of controlling four PWM gate drive signals for a 4-switch buckboost converter. Along with SM72295 (Photovoltaic Full Bridge Driver) it creates a solution for an MPPT configured DC-DC converter with efficiencies up to 98.5%. Integrated into the chip is an 8-channel, 12 bit A/D converter used to sense input and output voltage and current, as well as board configuration. Externally programmable values include maximum output voltage and current as well as different settings on slew rate, and soft-start. ■ ■ ■ ■ ■ ■ Renewable Energy Grade Programmable maximum power point tracking Photovoltaic solar panel voltage and current diagnostic Single inductor four switch buck-boost converter control VOUT Overvoltage protection Over-current protection Package ■ TSSOP-28 Block Diagram 30134202 FIGURE 1. Block Diagram © 2011 Texas Instruments Incorporated 301342 www.ti.com SM72441 Programmable Maximum Power Point Tracking Controller for Photovoltaic Solar Panels November 20, 2011 www.ti.com 2 FIGURE 2. Typical Application Circuit 30134201 SM72441 SM72441 Connection Diagram 30134203 Top View TSSOP-28 Ordering Information Order Number Description NSC Package Drawing Supplied As Package Top Mark SM72441MTX TSSOP-28 MTC28 2500 Units in Tape and Reel S72441 SM72441MTE TSSOP-28 MTC28 250 Units in Tape and Reel S72441 SM72441MT TSSOP-28 MTC28 48 Units in rail S72441 3 www.ti.com SM72441 Pin Descriptions Pin Name 1 RST Description Active low signal. External reset input signal to the digital circuit. 2 NC1 No Connect. This pin should be grounded. 3 VDDD Digital supply voltage. This pin should be connected to a 5V supply, and bypassed to VSSD with a 0.1uF monolithic ceramic capacitor. 4 VSSD 5 NC2 No Connect. This pin should be pulled up to the 5V supply using 10k resistor. 6 NC3 No Connect. This pin should be grounded using a 10k resistor. 7 NC4 No Connect. This pin should be grounded using a 10k resistor. 8 NC5 No Connect. This pin should be pulled up to 5V supply using 10k resistor. 9 NC6 No Connect. This pin should be pulled up to 5V supply using 10k resistor. 10 NC7 No Connect. This pin should be grounded. 11 LED LED pin outputs a pulse during normal operation. Digital ground. The ground return for the digital supply and signals. 12 VDDA Analog supply voltage. This voltage is also used as the reference voltage. This pin should be connected to a 5V supply, and bypassed to VSSA with a 1uF and 0.1uF monolithic ceramic capacitor. 13 VSSA 14 A0 15 AVIN 16 A2 17 A/D Input Channel 0. Connect a resistor divider to 5V supply to set the maximum output voltage. Please refer to application section for more information on setting the resistor value. A/D Input to sense input voltage. A/D Input Channel 2. Connect a resistor divider to 5V supply to set MPPT update rate. Please refer to application section for more information on setting the resistor value. AVOUT A/D Input to sense the output voltage. 18 A4 19 AIIN 20 A6 21 Analog ground. The ground return for the analog supply and signals. A/D Input Channel 4. Connect a resistor divider to 5V supply to set the maximum output current. Please refer to application section for more information on setting the resistor value. A/D Input to sense input current. A/D Input Channel 6. Connect a resistor divider to 5V supply to set the maximum output voltage slew rate. Please refer to application section for more information on setting the resistor value. AIOUT A/D Input to sense the output current. 22 NC8 No Connect. This pin should be grounded using a 10k resistor. 23 NC9 No Connect. This pin should be connected with 150k pull-up resistor to 5V supply. 24 LIB Low side boost PWM output. 25 HIB High side boost PWM output. 26 HIA High side buck PWM output. 27 LIA Low side buck PWM output. 28 OVP www.ti.com Overvoltage Protection Pin. Active Low. SM72441 will reset once voltage on this pin drops below its threshold voltage. 4 Recommended Operating Conditions If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. Analog Supply Voltage VA (VDDA -VSSA) Analog Supply Voltage VD (VDDD -VSSD) Voltage on Any Pin to GND Input Current at Any Pin (Note 3) Package Input Current (Note 3) Storage Temperature Range ESD Rating (Note 2) Human Body Model SM72441 Absolute Maximum Ratings (Note 1) Operating Temperature VA Supply Voltage VD Supply Voltage Digital Input Voltage Analog Input Voltage Junction Temperature -0.3 to 6.0V -0.3 to VA +0.3V max 6.0V -0.3 to VA +0.3V ±10 mA ±20 mA -65°C to +150°C -40°C to 105°C +4.75V to +5.25V +4.75V to VA 0 to VA 0 to VA -40°C to 125°C 2 kV Specifications in standard typeface are for TJ = 25°C, and those in boldface type apply over the full operating junction temperature range.(Note 3) Symbol Parameter Conditions Min Typ Max Units - 0 to VA - V ANALOG INPUT CHARACTERISTICS AVin, AIin AVout, AIout Input Range IDCL DC Leakage Current CINA Input Capacitance(Note 4) VERR DC Voltage Measurement Accuracy - - ±1 µA Track Mode - 33 - pF Hold Mode - 3 - pF 0.1 % DIGITAL INPUT CHARACTERISTICS VIL Input Low Voltage - - 0.8 V VIH Input High Voltage 2.8 - - V CIND Digital Input Capacitance(Note 4) - 2 4 pF IIN Input Current - ±0.01 ±1 µA VD-0.5 - - V - - 0.4 V ±1 µA 2 4 pF 4.75 5 5.25 V 7 10 15 mA 50 78 mW DIGITAL OUTPUT CHARACTERISTICS VOH Output High Voltage ISOURCE = 200 µA VA = VD = 5V VOL Output Low Voltage ISINK = 200 µA to 1.0 mA VA = VD = 5V IOZH , IOZL Hi-Impedance Output Leakage Current VA = VD = 5V COUT Hi-Impedance Output Capacitance (Note 4) POWER SUPPLY CHARACTERISTICS (CL = 10 pF) VA ,VD Analog and Digital Supply Voltages VA ≥ VD IA + ID Total Supply Current VA = VD = 4.75V to 5.25V PC Power Consumption VA = VD = 4.75V to 5.25V PWM OUTPUT CHARACTERISTICS fPWM PWM switching frequency 210 kHz tDEAD Dead time 38 ns Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings indicate conditions for which the device is intended to be functional, but does not guarantee specific performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Note 3: Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL). Note 4: Not tested. Guaranteed by design. 5 www.ti.com SM72441 photovoltaic module. MPPT performance is very fast. Convergence to the maximum power point of the module typically occurs within 0.01s. This enables the controller to maintain optimum performance under fast-changing irradiance conditions. Transitions between buck, boost, and buck-boost modes are smoothed, and advanced digital PWM dithering techniques are employed to increase effective PWM resolution. Output voltage and current limiting functionality are integrated into the digital control logic. The controller is capable of handling both shorted and no-load conditions and will recover smoothly from both. Operation Description OVERVIEW The SM72441 is a programmable MPPT controller capable of outputting four PWM gate drive signals for a 4-switch buckboost converter. The typical application circuit is shown in Figure 2. The SM72441 uses an advanced digital controller to generate its PWM signals. A maximum power point tracking (MPPT) algorithm monitors the input current and voltage and controls the PWM duty cycle to maximize energy harvested from the 30134204 FIGURE 3. High Level State Diagram for Startup STARTUP SM72441 has a soft start feature that will ramp its output voltage for a fixed time of 250ms. MPPT mode will be entered during soft start if the load current exceeded the minimum current threshold. Otherwise, buck-boost operation is entered after soft-start is finished where the ratio between input and output voltage is 1:1. Refer to Figure 3 for a high level state diagram of startup. The current threshold to transition between MPPT to standby (buck-boost) mode and vice versa can be set by feeding the output of current sensing amplifier (Figure 2) to the AIIN and AIOUT pin. For an appropriate voltage level, refer to AIIN and AIOUT section of this datasheet. 30134205 FIGURE 4. Start-Up Waveforms of Controlled Output www.ti.com 6 AVIN PIN AVIN pin is an A/D input to sense the input voltage of SM72441. A resistor divider can be used to scale the max voltage to about 4V, which is 80% of the full scale of the A/D input. CONFIGURABLE SETTINGS The voltage on A0 sets the max output voltage; whereas the voltage on A2 enables MPPT update rate and limits the max boost ratio when output current is below the standby threshold. Output current limit is set by the voltage on A4 and output voltage slew rate limit is set on A6. In order to set a slew rate limit of 125V/sec, the ratio of the two resistors in A6 should be 9:1. The low current condition is detected if the voltage on AIIN is less than 0.488V (rising) and 0.293 (falling) + ΔI or if the voltage on AIOUT is less than 0.488 V (rising) and 0.293 (falling) + ΔI. If low current is detected, the converter operates in standby mode and limit the maximum duty cycle to either a 1 (buck-boost), 1.15 (boost) or 1.25 (boost) conversion ratio (programmable). In this case no MPPT will be performed. The actual value of current will depend on the gain of the current sensing amplifier circuitry that feeds the AIIN and AIOUT pins. For more complete information on the various settings based on the voltage level of A2, please refer to Table 1 below. Vfs denotes the full scale voltage of the ADC which is equal to VDDA where VDDA is a reference voltage to analog ground. A typical value for top configuration resistors (RT1 to RT4) should be 20 kΩ. Where RT1 and RB1 are the resistor divider on the ADC pin A0 and RFB1 and RFB2 are the output voltage feedback resistors. A typical value for RFB2 is about 2 kΩ. CURRENT LIMIT SETTING Maximum output current can be set by changing the resistor divider on A4 (pin 18). (Refer to Figure 2 ). Overcurrent at the output is detected when the voltage on AIOUT (pin 21) equals to the voltage on A4 (pin 18). The voltage on A4 can be set by a resistor divider connected to 5V whereas a current sense amplifier output can be used to set the voltage on AIOUT. AIIN AND AIOUT PIN These two pins are used to set current threshold from standby (buck-boost mode) to MPPT mode and from MPPT mode into standby mode. In order to transition from standby to MPPT mode, the following conditions have to be satisfied: 1) AIIN and AIOUT voltage > 0.488V 2) Iout < Iout_max On the other hand, in order to transition from MPPT to standby mode, the following condition have to be satisfied: 1) AIIN and AIOUT voltage < 0.293V 2) Iout < Iout_max TABLE 1. List of configurable modes on ADC Channel 2 ADC Channel 2 MPPT Update Time Slew Rate Detection Low Current Detection Initial Boost Ratio Delta I 0 < VADC2 < Vfs/16 1.2 ms Disabled Disabled N/A N/A 1Vfs/16 < VADC2 <2Vfs/16 38 ms Disabled Disabled N/A N/A 2Vfs/16 < VADC2 <3Vfs/16 77 ms Disabled Disabled N/A N/A 3Vfs/16 < VADC2 <4Vfs/16 38 ms Enabled Disabled N/A N/A 4Vfs/16 < VADC2 <5Vfs/16 38 ms Enabled Enabled 1.15 60 (0.3 A) 5Vfs/16 < VADC2 <6Vfs/16 38 ms Enabled Enabled 1.15 90 (0.45 A) 6Vfs/16 < VADC2 <7Vfs/16 38 ms Enabled Enabled 1.15 120(0.6 A) 7Vfs/16 < VADC2 <8Vfs/16 38 ms Enabled Enabled 1.25 60 8Vfs/16 < VADC2 <9Vfs/16 38 ms Enabled Enabled 1.25 90 9Vfs/16 < VADC2 <10Vfs/16 38 ms Enabled Enabled 1.25 120 10Vfs/16 < VADC2 <11Vfs/16 77 ms Enabled Enabled 1.15 60 11Vfs/16 < VADC2 <12Vfs/16 77 ms Enabled Enabled 1.15 90 12Vfs/16 < VADC2 <13Vfs/16 77 ms Enabled Enabled 1.15 120 13Vfs/16 < VADC2 <14Vfs/16 77 ms Enabled Enabled 1.25 60 14Vfs/16 < VADC2 <15Vfs/16 77 ms Enabled Enabled 1.25 90 15Vfs/16 < VADC2 <16Vfs/16 77 ms Enabled Enabled 1.25 120 7 www.ti.com SM72441 Current limit is triggered when AIOUT (pin 21) voltage is equal to A4 (pin 18). MAXIMUM OUTPUT VOLTAGE Maximum output voltage on the SM72441 is set by resistor divider ratio on pin A0. (Please refer to Figure 2 Typical Application Circuit). SM72441 puts is 0V to VA. Going beyond this range will cause the ESD diodes to conduct and result in erratic operation. The capacitor C1 in Figure 6 has a typical value of 3 pF and is mainly the package pin capacitance. Resistor R1 is the on resistance of the multiplexer and track / hold switch; it is typically 500Ω. Capacitor C2 is the ADC sampling capacitor; itis typically 30 pF. The ADC will deliver best performance when driven by a low-impedance source (less than 100Ω). This is especially important when sampling dynamic signals. Also important when sampling dynamic signals is a band-pass or low-pass filter which reduces harmonic and noise in the input. These filters are often referred to as anti-aliasing filters. RESET PIN When the reset pin is pulled low, the chip will cease its normal operation and turn-off all of its PWM outputs. Below is an oscilloscope capture of a forced reset condition. 30134208 FIGURE 5. Reset Operational Behavior 30134209 As seen in Figure 5, the initial value for output voltage and load current are 28V and 1A respectively. After the reset pin is grounded, both the output voltage and load current decreases immediately. MOSFET switching on the buck-boost converter also stops immediately. VLOB indicates the low side boost output from the SM72295. FIGURE 6. Equivalent Input Circuit DIGITAL INPUTS and OUTPUTS The digital input signals have an operating range of 0V to VA, where VA = VDDA - VSSA. They are not prone to latchup and may be asserted before the digital supply VD, where VD = VDDD - VSSD, without any risk. The digital output signals operating range is controlled by VD. The output high voltage is VD – 0.5V (min) while the output low voltage is 0.4V (max). ANALOG INPUT An equivalent circuit for one of the ADC input channels is shown in Figure 6. Diode D1 and D2 provide ESD protection for the analog inputs. The operating range for the analog in- www.ti.com 8 SM72441 Physical Dimensions inches (millimeters) unless otherwise noted NS Package Drawing MTC28 9 www.ti.com SM72441 Programmable Maximum Power Point Tracking Controller for Photovoltaic Solar Panels Notes TI/NATIONAL INTERIM IMPORTANT NOTICE Texas Instruments has purchased National Semiconductor. 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