sm72442太阳能MPPT

SM72442March 13, 2012Programmable Maximum Power Point Tracking Controllerfor Photovoltaic Solar PanelsGeneral DescriptionThe SM72442 is a programmable MPPT controller capable ofcontrolling four PWM gate drive signals for a 4-switch buck-boost converter. The SM72442 also features a proprietaryalgorithm called Panel Mode which allows for the panel to beconnected directly to the output of your power optimizer cir-cuit. Along with the SM72295 Photovoltaic Full Bridge Driv-er, it creates a solution for an MPPT configured DC-DCconverter with efficiencies up to 99.5. Integrated into thechip is an 8-channel, 12 bit A/D converter used to sense inputand output voltages and currents, as well as board configu-ration. Externally programmable values include maximumoutput voltage and current as well as different settings forslewrate, soft-start and Panel Mode.Features■ Renewable Energy Grade■ Programmable maximum power point tracking■ Photovoltaic solar panel voltage and current diagnostic■ Single inductor four switch buck-boost converter control■ I2C interface for communication■ VOUT Overvoltage protection■ Over-current protectionPackage■ TSSOP-28Block Diagram30134302FIGURE 1. Block Diagram 2012 Texas Instruments Incorporated 301343 SNVS689G www.ti.comSM72442 Programmable Maximum Power Point Tracking Controller for Photovoltaic SolarPanels30134301FIGURE2.TypicalApplicationCircuitwww.ti.com 2SM72442Connection Diagram30134303FIGURE 3. Top ViewTSSOP-28Ordering InformationOrder Number Description NSC Package Drawing Supplied As Package Top MarkingSM72442MTX TSSOP-28 MTC28 2500 Units in Tape andReelSO2442SM72442MTE TSSOP-28 MTC28 250 Units in Tape andReelSO2442SM72442MT TSSOP-28 MTC28 48 Units in Rail SO24423 www.ti.comSM72442Pin DescriptionsPin Name Description1 RST Active low signal. External reset input signal to the digital circuit.2 NC1 Reserved for test only. 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 0.1 μ F monolithicceramic capacitor.4 VSSD Digital ground. The ground return for the digital supply and signals.5 NC2 No Connect. This pin should be pulled up to the 5V supply using 10k resistor.6 I2C0 Addressing for I2C communication.7 I2C1 Addressing for I2C communication.8 SCL I2C clock.9 SDA I2C data.10 NC3 Reserved for test only. This pin should be grounded.11 PM_OUT When Panel Mode is active, this pin will output a 400 kHz square wave signal with amplitude of 5V. Otherwise, itstays low.12 VDDA Analog supply voltage. This voltage is also used as the reference voltage. This pin should be connected to a 5Vsupply, and bypassed to VSSA with a 1 μ F and 0.1 μ F monolithic ceramic capacitor.13 VSSA Analog ground. The ground return for the analog supply and signals.14 A0 A/D Input Channel 0. Connect a resistor divider to 5V supply to set the maximum output voltage. Please refer tothe application section for more information on setting the resistor value.15 AVIN Input voltage sensing pin.16 A2 A/D Input Channel 2. Connect a resistor divider to a 5V supply to set the condition to enter and exit Panel ModePM. Refer to configurable modes for SM72442 in the application section.17 AVOUT Output voltage sensing pin.18 A4 A/D Input Channel 4. Connect a resistor divider to a 5V supply to set the maximum output current. Please refer tothe application section for more information on setting the resistor value.19 AIIN Input current sensing pin.20 A6 A/D Input Channel 6. Connect a resistor divider to a 5V supply to set the output voltage slew rate and various PMconfigurations. Refer to configurable modes for SM72442 in the application section.21 AIOUT Output current sensing pin.22 I2C2 Addressing for I2C communication.23 NC4 No Connect. This pin should be connected with 60.4k pull-up resistor to 5V.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 PM Panel Mode Pin. Active low. Pulling this pin low will force the chip into Panel Mode.www.ti.com 4SM72442Absolute Maximum Ratings Note 1 If Military/Aerospace specified devices are required,please contact the Texas Instruments Sales Office/Distributors for availability and specifications.Analog Supply Voltage V AVDDA - VSSA-0.3 to 6.0VDigital Supply Voltage V DVDDD - VSSD-0.3 to V A 0.3Vmax 6.0VVoltage on Any Pin to GND -0.3 to V A 0.3VInput Current at Any Pin Note 3 10 mAPackage Input Current Note 3 20 mAStorage Temperature Range -65 C to 150 CESD Rating Note 2 Human Body Model 2 kVRecommended OperatingConditionsOperating Temperature -40 C to 105 CVA Supply Voltage 4.75V to 5.25VVD Supply Voltage 4.75V to V ADigital Input Voltage 0 to V AAnalog Input Voltage 0 to V AJunction Temperature -40 C to 125 CSpecifications in standard typeface are for T J 25 C, and those in boldface type apply over the full operating junction temperaturerange. Note 3 Symbol Parameter Conditions Min Typ Max UnitsANALOG INPUT CHARACTERISTICSAVin, AIinAVout, AIout Input Range - 0 to V A - VI DCL DC Leakage Current - - 1 μACINA Input Capacitance Note 4 Track Mode - 33 - pFHold Mode - 3 - pFDIGITAL INPUT CHARACTERISTICSV IL Input Low Voltage - - 0.8 VV IH Input High Voltage 2.8 - - VCIND Digital Input Capacitance Note 4 - 2 4 pFI IN Input Current - 0.01 1 μADIGITAL OUTPUT CHARACTERISTICSV OH Output High Voltage ISOURCE 200 μ A VA V D 5V VD - 0.5 - - VV OL Output Low Voltage ISINK 200 μ A to 1.0 mA VA V D 5V - - 0.4 VI OZH , I OZL Hi-Impedance Output LeakageCurrent VA V D 5V 1 μACOUT Hi-Impedance OutputCapacitance Note 4 2 4 pFPOWER SUPPLY CHARACTERISTICS C L 10 pFV A ,V D Analog and Digital SupplyVoltages VA ≥ V D 4.75 5 5.25 VI A I D Total Supply Current VA V D 4.75V to 5.25V - 11.5 15 mAP C Power Consumption VA V D 4.75V to 5.25V 57.5 78.75 mWPWM OUTPUT CHARACTERISTICSf PWM PWM switching frequency 220 kHzNote 1 Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operationof the device is guaranteed. Operating Ratings do not imply guaranteed 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 k 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 StatisticalQuality 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.comSM72442Operation DescriptionOVERVIEWThe SM72442 is a programmable MPPT controller capable ofoutputting four PWM gate drive signals for a 4-switch buck-boost converter with an independent Panel Mode. The typicalapplication circuit is shown in Figure 2 .The SM72442 uses an advanced digital controller to generateits PWM signals. A maximum power point tracking MPPTalgorithm monitors the input current and voltage and controlsthe PWM duty cycle to maximize energy harvested from thephotovoltaic module. MPPT performance is very fast. Con-vergence to the maximum power point of the module typicallyoccurs within 0.01s. This enables the controller to maintainoptimum performance under fast-changing irradiance condi-tions.Transitions between buck, boost, and Panel Mode aresmoothed and advanced digital PWM dithering techniquesare employed to increase effective PWM resolution. Outputvoltage and current limiting functionality are integrated intothe digital control logic. The controller is capable of handlingboth shorted and no-load conditions and will recover smoothlyfrom both conditions.30134304FIGURE 4. High Level State Diagram for Startupwww.ti.com 6SM72442STARTUPSM72442 has a soft start feature that will ramp its output volt-age for a fixed time of 250ms.If no output current is detected during soft-start time, the chipwill then be in Panel Mode for 60 seconds. A counter will startonce the minimum output current threshold is met set by ADCinput channel 4. During these 60 seconds, any variation onthe output power will not cause the chip to enter MPPT mode.Once 60 seconds have elapsed, at a certain power level vari-ation at the output set by ADC input channel 2 will engagethe chip in MPPT mode.If the output current exceeded the current threshold set atA/D Channel 6 A6 during soft-start, the chip will then engagein MPPT mode.30134305FIGURE 5. Startup SequenceMAXIMUM OUTPUT VOLTAGEMaximum output voltage on the SM72442 is set by resistordivider ratio on pin A0. Please refer to Figure 2 Typical Ap-plication Circuit.Where RT1 and RB1 are the resistor divider on the ADC pinA0 and RFB1 and RFB2 are the output voltage sense resis-tors. A typical value for RFB2 is about 2 k CURRENT LIMIT SETTINGMaximum output current can be set by changing the resistordivider on A4 pin 18. Refer to Figure 2 . Overcurrent at theoutput is detected when the voltage on AIOUT pin 21 equalsthe voltage on A4 pin 18. The voltage on A4 can be set bya resistor divider connected to 5V whereas the voltage onAIOUT can be set by a current sense amplifier.AVIN PINAVIN is an A/D input to sense the input voltage of theSM72442. A resistor divider can be used to scale max voltageto about 4V, which is 80 of the full scale of the A/D input.CONFIGURABLE SETTINGSA/D pins A0, A2, A4, and A6 are used to configure the be-havior of the SM72442 by adjusting the voltage applied tothem. One way to do this is through resistor dividers as shownin Figure 2 , where RT1 to RT4 should be in the range of 20k.Different conditions to enter and exit Panel Mode can be seton the ADC input channel 2. Listed below are different con-ditions that a user can select on pin A2. “ 11 ” refers to the statein which the DC/DC converter operates with its output voltageequal to its input voltage also referred to as “ Buck-Boost ”mode on Figure 4.A2 Entering Panel Mode Exiting Panel Mode4.69 V 2s in 11 Mode 3.1 power variation4.06 V 1s in 11 Mode 3.1 power variation3.44 V 0.4s in 11 Mode 3.1 power variation2.81 V 0.2s in 11 Mode 3.1 power variation2.19 V 2s in 11 Mode 1.6 power variation1.56 V 1s in 11 Mode 1.6 power variation0.94 V 0.4s in 11 Mode 1.6 power variation0.31 V 0.2s in 11 Mode 1.6 power variationThe user can also select the output voltage slew rate, mini-mum current threshold and duration of Panel Mode after thesoft-start period has finished, by changing the voltage levelon pin A6 which is the input of ADC channel 6.A6 Output VoltageSlew Rate LimitStarting PanelMode TimeMPPT ExitThresholdMPPT StartThresholdStarting boost ratio4.69 V Slow Not applicable 0 mA 0 mA 114.06 V Slow 60s 75mA 125mA 113.44 V Slow 0s 300mA 500mA 112.81 V Slow 120s 300mA 500mA 112.19 V Slow Not applicable 300mA 500mA 11.21.56 V Slow 60s 300mA 500mA 110.94 V Fast 60s 300mA 500mA 110.31 V No slew rate limit 60s 300mA 500mA 117 www.ti.comSM72442PARAMETER DEFINITIONSOutput Voltage Slew Rate Limit Settling Time Time con-stant of the internal filter used to limit output voltage change.For fast slew rate, every 1V increase, the output voltage willbe held for 30 ms whereas in a slow slew rate, the outputvoltage will be held for 62 ms for every 1V increase. SeeFigure 6 .Starting PM Time After initial power-up or reset, the outputsoft-starts and then enters Panel Mode for this amount oftime.MPPT Exit Threshold and MPPT Start Threshold Theseare the hysteretic thresholds for Iout_th.Starting Boost Ratio – This is the end-point of the soft-startvoltage ramp. 11 ratio means it stops when Vout Vin, 11.2means it stops when Vout 1.2 x Vin.PANEL MODE PIN PM PINThe SM72442 can be forced into Panel Mode by pulling thePM pin low. One sample application is to connect this pin tothe output of an external temperature sensor; therefore when-ever an over-temperature condition is detected the chip willenter a Panel Mode.Once Panel Mode is enabled either when buck-boost modeis entered for a certain period of time adjustable on channel2 of ADC or when PM is pulled low, the PM_OUT pin willoutput a 400 kHz square wave signal. Using a gate driver andtransformer, this square wave signal can then be used to drivea Panel Mode FET as shown in Figure 7 .30134313FIGURE 6. Slew Rate Limitation Circuit30134307FIGURE 7. Sample Application for Panel Mode Operationwww.ti.com 8SM72442RESET PINWhen the reset pin is pulled low, the chip will cease its normaloperation and turn-off all of its PWM outputs including theoutput of PM_OUT pin. Below is an oscilloscope capture of aforced reset condition.30134308FIGURE 8. Forced Reset ConditionAs seen in Figure 8 , the initial value for output voltage andload current are 28V and 1A respectively. After the reset pinis grounded both the output voltage and load current de-creases immediately. MOSFET switching on the buck-boostconverter also stops immediately. VLOB indicates the lowside boost output from the SM72295.ANALOG INPUTAn equivalent circuit for one of the ADC input channels isshown in Figure 9 . Diode D1 and D2 provide ESD protectionfor the analog inputs. The operating range for the analog in-puts is 0V to V A. Going beyond this range will cause the ESDdiodes to conduct and result in erratic operation.The capacitor C1 in Figure 9 has a typical value of 3 pF andis mainly the package pin capacitance. Resistor R1 is the onresistance of the multiplexer and track / hold switch; it is typ-ically 500 . Capacitor C2 is the ADC sampling capacitor; it istypically 30 pF. The ADC will deliver best performance whendriven by a low-impedance source less than 100 . This isspecially important when sampling dynamic signals. Also im-portant 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.30134309FIGURE 9. Equivalent Input CircuitDIGITAL INPUTS and OUTPUTSThe digital input signals have an operating range of 0V toVA, where V A VDDA – VSSA. They are not prone to latch-up and may be asserted before the digital supply V D, whereVD VDDD – VSSD, without any risk. The digital output sig-nals operating range is controlled by V D . The output highvoltage is V D – 0.5V min while the output low voltage is 0.4Vmax.SDA and SCL OPEN DRAIN OUTPUTSCL and SDA output is an open-drain output and does nothave internal pull-ups. A “ high ” level will not be observed onthis pin until pull-up current is provided by some externalsource, typically a pull-up resistor. Choice of resistor valuedepends on many system factors; load capacitance, tracelength, etc. A typical value of pull- up resistor for SM72442ranges from 2 k to 10 k . For more information, refer to theI2C Bus specification for selecting the pull-up resistor value .The SCL an