Hybrid Battery Charger With Load Control for Telecom Equipment
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Application Report SLPA013 – October 2014 Hybrid Battery Charger With Load Control for Telecom Equipment ABSTRACT Commercial telecom equipment needs multiple power input systems to ensure continuous network connectivity. The load must be backed up to different sources. This application note describes a synchronous-buck-based reference design using MSP430 and CSD87350 power blocks, which use multiple OR’ed inputs (solar and AC/DC adaptor) to charge a 12-V SLA battery. Priority charging is used when solar energy is available. Seamless transfer between two sources ensures battery is always charged when inputs are available. It runs MPPT algorithms to charge while on solar input and conventional CC/CV charging when working from an adaptor input. Multiple protection schemes ensure it is a robust design. Topic ........................................................................................................................... Page 1 Design Specifications ........................................................................................... 2 2 Block Diagram ..................................................................................................... 2 3 System Explanation and Design ............................................................................ 3 4 Software Flow...................................................................................................... 4 5 Schematics ......................................................................................................... 9 6 Test Results ...................................................................................................... 11 SLPA013 – October 2014 Hybrid Battery Charger With Load Control for Telecom Equipment 1 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
Design Specifications www.ti.com 1 Design Specifications Table 1. Design Specifications Parameter Description Value Panel 16.5 to 21 V VIN range Adaptor 15.5 to 16 V Battery specifications Capacity 12 V, 100 Ah Charging current 7A Charging specifications Voltage during CV mode charging 14.2 V FSW Switch frequency 100 kHz Load current 4A Output specifications Output voltage 10.2 to 14.2 V • Hot swappable load • Output short circuit • Reverse polarity protection Protection features • Two level overcurrent protection • Battery UVLO • Overtemperature protection 2 Block Diagram Figure 1 shows the block level implementation of the system. 100-W 12-V Solar Panel Temp Sensor Input Current Sync Buck Output Current Load Current Oring Control Load Switch Sense Converter Sense Sense Telecom Microcontroller VBAT ICS Equipment VPANEL Universal OCS LCS AC Adaptor (15 V at 7-A Capacity) LDO Figure 1. 2 Hybrid Battery Charger With Load Control for Telecom Equipment SLPA013 – October 2014 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
www.ti.com System Explanation and Design 3 System Explanation and Design 3.1 Power Source Control and Monitoring The telecom equipment (load) is always powered either from a solar panel, AC/DC adaptor, or the battery. As long as solar energy from the panel is available, priority charging is used to deliver the required power (average 17 V and current sufficient enough to manage load or to charge battery). If panel voltage drops below adapter (15 V), the charge controller microcontroller turns off the panel switch and turns on the AC/DC adapter switch, which also ensures no leakage of the stronger source into the weaker one. Two 30-V, ultra-low RDS(on) FETs from TI (CSD17527Q5A) are selected for this purpose. The simple transistor is used for proving the drive from the microcontroller. 3.2 Synchronous Buck Power Stage The synchronous buck convertor has better efficiency and lower loss compared to asynchronous topology because a diode on the bottom side is replaced with a low RDS(on) value. A single 30-V, 25-A power block from TI (CSD87350Q5D) is selected for this. The advantage of a power block is the smaller package and ease of layout eliminating parasitics of board layout of high frequency hot nodes. The microcontroller PWM module can generate multiple PWMs on the same timer base. Each output can be configured for different output modes, for example, toggle, reset/on, reset/off, always on, and so forth. With this flexible logic, the user can achieve complimentary logic with required dead band. However, a driver UCC27211 is used to enable ease of driving. The other power stage components (inductor and capacitor) calculations are designed using standard equations of the buck converter based on the prior specifications. • LOUT (cal) = 12.67 μH, selected LOUT = 10 μH, from Wurth Electronics • Selected COUT = 47 µF × 1; 22 µF × 2 3.3 Current Sense Inputs To ensure continuity to ground loop, a high-side sense circuit was used. A zero-drift instrumentation amplifier from TI, INA282, with a 50-V/V gain, wide common-mode input range is selected for this application. 3.4 Load Management A simple load switch with hotswap control from TI TPS25910 is used for monitoring the load behavior. If there is any short or overload, it immediately trips sending it into a hiccup mode on the load. The fast-trip comparator of the microcontroller also quickly disables the PWM. This is second-level protection for the load. To prevent the load from discharging back into the source, a blocking FET (CSD17313Q2) from TI is used. It is controlled by the load switch. 3.5 Microcontroller A MSP430F5132 microcontroller is used in this application. See Section 4 for further details of the software routines. 3.6 LDO and Temperature Sensor A simple OR’ed supply is used as the input of the LDO to ensure that power to the controller is always available to sense any inappropriate condition. The 3.3 V generated by the LDO (TPS73801) is used to power the MCU, LEDs, instrumentation amplifiers, and a simple thermostat TMP709, which is used for tripping the load in case there is any abnormal increase in the temperature. 3.7 Battery Management The section explains the battery management software portion in the microcontroller. It checks for the state-of-charge of the battery and applies the charging profile appropriately. This application uses a lead- acid battery. The following list shows the battery properties that are considered while charging. • Minimum 2.10 V per cell is considered as a good battery • Cells in a string are not the same strength, some are weak and some are strong. SLPA013 – October 2014 Hybrid Battery Charger With Load Control for Telecom Equipment 3 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
System Explanation and Design www.ti.com • Should not be charged above 50°C • Overcharging increases the risk of hydrogen gassing on the positive plate. • Undercharging increases sulfation on the negative plate. • Battery charge profile is in constant current mode until battery attains, for example, 70%, constant voltage mode from 70% to 90% and float charge after that. 3.8 Maximum Power Point Tracking Algorithm A simple MPPT algorithm known as perturb and observe is used for controlling this system. As explained in the PWM Resolution section, every one count of PWM timer yields 0.04% of duty cycle variation, which is “fine” enough to achieve smoother and slower tracking. With this at MPP stage, there will be 0.04% oscillation which may be negligible in a low-power application. If duty cycle variation is increased more than 1 count, tracking is faster and reduces the variation to minimize the MPP stage oscillations. This also resembles incremental conductance method. It monitors battery/load current with respect to ΔV applied to the converter, increasing the ΔV drives to MPP faster and at the MPP stage reduces the ΔV and settles smoothly at MPP. 4 Software Flow This application uses the MSP430F5132 microcontroller. The following are key features, which enable efficient usage of resources to achieve an efficient solar power convertor. MSP430F5132 key features supporting efficiency expectation: • Fully operates from 3.6 to 1.8 V • Only 180-µA/MHz active current, lowest current at shut down is 0.25 µA • Fast wake-up, less than 5 µs from stand by • 200 KSPS, 10-bit ADC, with just 110-µA current consumption with built-in reference • Hi-resolution timer/PWM = 4-ns minimum pulse duration, 250-µA current consumption 4.1 PWM Resolution The MSP430F5132 has a special hi-resolution timer, timer-D. This timer can be programmed to generate high switching frequency to accommodate a smaller inductor's size. This timer is clocked from the following sources: • MCLK/SMCLK – Maximum range is 16 MHz • ACLK – Maximum 32 kHz • Special timer-D clock generator of the following values: – 64 MHz – 128 MHz – 200 MHz – 256 MHZ Effective number of bits (ENOB) is an important parameter in achieving smoother control, thereby reducing switching noise and protecting the battery from stress caused by larger voltage variations caused in a low-resolution system. ENOB = Log2(Module clock / Output frequency) (1) This application requires 100-kHz switching frequency. Therefore, the following settings provide, Module clock = 256 MHz Output frequency = 100 kHz ENOB = 11.36 bits VOUT = D × VIN where • D = Duty cycle or on-time of the switch 4 Hybrid Battery Charger With Load Control for Telecom Equipment SLPA013 – October 2014 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
www.ti.com Software Flow • VIN = Input voltage (from battery, solar panel, or ACDC adapter) • VOUT = Output voltage (2) Consider the converter to be 100% efficient. Therefore, no loss factor is taken into account in this calculation. For a single bit change in D varies by approximately 4 ns in a 100-kHz period wave, which is 0.038% of VIN; if a VIN of 17, VOUT varies by 0.00646 V. 4.2 ADC Module This device has 10-bit SAR ADC, speed can be configured for 50ksps for low power or 200ksps for faster processing. This application can go slow, which helps to conserve additional power loss caused by the ADC module itself (refer to the data sheet for power consumption data). This module can be operated independently without sharing the CPU clock. Hence, the CPU can be placed in low-power mode, enabling only the ADC to function. A special ADC DMA can be configured to scan all channels and interrupt the CPU when data is available at the RAM for further processing. This application requires 6 channels: battery current, panel current, battery voltage, panel voltage, load current, and temperature sensor. Therefore, a 6-channel conversion is required every loop, until then the CPU can be put in IDLE to conserve power. 4.3 ADC Measurement Range This MCU has a 10-bit SAR ADC, input voltage range is 0 V to AVCC, which can be up to 3.6 V (refer to data sheet for more electrical data). Hence, input signal strength can be from 3.3 mV per count of ADC until 3.3 V (1023 counts) can be sensed. Sense resistors are 5 mΩ. Hence, minimum current sensible from panel/load/battery with a gain of 50 is about 13 mA. Power on/ Reset Source Source S1 S2 Panel V x I Adapter V x I Select S1, Select S2, Turn OFF S2 S1 ≥ S2 Turn OFF S1 Init ADC Init PWM Init Comparator for Tripping Start Control Loop Figure 2. Initialization Flow Chart SLPA013 – October 2014 Hybrid Battery Charger With Load Control for Telecom Equipment 5 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
Software Flow www.ti.com ADC Interrupt every 100 ms SAMPLE • Panel Voltage (P_V) • Panel Current (P_I) • Battery Voltage(B_V) • Battery Current(B_I) Wait for ADC • Adaptor Voltage (A_V) Interrupt • Load Current(A_I) Yes • Disable Battery Charging Algorithm B_V > P_V && • Only Load Management Thread B_V > A_V • Turn OFF Panel and Adaptor Indicator LEDs Yes • Panel Switch OFF, Adaptor switch ON P_V < A_V && • Turn OFF Panel LED and Turn ON Adaptor P_I ~= 0* Indicator LED • Load Management and CC/CV Mode • Adaptor Switch OFF, Panel switch ON Yes P_V > A_V • Turn OFF Adaptor LED and Turn ON Panel && P_I > Lowest Indicator LED Threshold* P_V > B_V Yes • Call Current Control (MPPT) and Load && P_I > Threshold Management No • Load Management Figure 3. Control Loop Flow Chart 6 Hybrid Battery Charger With Load Control for Telecom Equipment SLPA013 – October 2014 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
www.ti.com Software Flow Current Control Loop Start (MPPT) Sample Battery Current I_B(n) Yes No I_B(n) > I_B(n-1) Increment PWM Decrement PWM Duty Cycle Count Duty Cycle Count Figure 4. MPPT Algorithm Flow Chart Charge < 20% Charge > 95% State of Charge Charge > 70% Fast Charge Topping Charge Float Charge CC Mode CV Mode Short Safety Test Temp Open Fault Wait Figure 5. Battery Management Flow Chart SLPA013 – October 2014 Hybrid Battery Charger With Load Control for Telecom Equipment 7 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
Software Flow www.ti.com ADC Interrupt Every 100 ms Run MPPT Run CC/CV Charging Loop Charging Loop if Solar Panel if Adapter Powered Powered Run Battery Run Load Management Management Loop Loop CPU Idle State Figure 6. Control Loop Logic 8 Hybrid Battery Charger With Load Control for Telecom Equipment SLPA013 – October 2014 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
www.ti.com Schematics 5 Schematics PANEL CONNECTOR BATTERY CHARGER CIRCUIT R12 Q4 L2 P+ VP CONV_OUT J2 10 mΩ CSD87350Q5D 10 µH CONN-RMC-2PIN 1 2512 2 QFN5X6MM_DUAL DNP 1 1 VIN1 VSW3 8 2 1 CONN-RMC-2PIN R30 1 2 VSW2 7 L1 1 2 2 C31 + 10 µH CONN-RMC-2PIN R37 R13 1000 µF C32 3 6 10 mΩ 20 kΩ 10 mΩ 4.7 µF TG VSW1 2 1 2512 R603 2512 4 5 IND_74436xxxx BAT+ TGR BG PGND BAT+ R14 C11 + C12 C13 C15 C16 R31 3.01 + K 1206 47 µF 47 µF 22 µF 22 µF 22 µF 1 2 9 D7 CAP_EEUCF CAP_EEUCF C603 C603 C603 LED R44 10 mΩ 2512 Q3 1 kΩ CSD17527Q5A C14 A QFN5X6MM 3 2.2 nF 2 D10 C603 5 1 C17 C19 MMBZ5237 P- 1 µF 0.22 uF C603 C603 R15 U11 BAT+ V3V3 R16 1206 INA28xAID 1206 SO8 R17 4 U7 1 8 R27 VP -IN +IN P+ 1 kΩ UCC27211_D_8 2 7 0Ω R603 3 GND REF1 6 R603 1 8 4 REF2 V+ 5 2 VDD LO 7 NC OUT 3 HB VSS 6 HO LI IP_SNS C18 4 5 C HS HI C24 B Q5 0.01 µF 0.1 µF PAN_SW MMBT2222ALT1 C603 C603 R32 SOT23 PANEL CURRENT SENSE E 1 kΩ R46 2 kΩ R603 R38 BUCK_PWM 10 kΩ R603 SYNCB_PWM R45 2 kΩ U13 V3V3 C33 R43 R42 C34 INA28xAID DNP DNP SO8 CONV_OUT 100 p 100 p 1 8 R28 BAT+ -IN +IN 2 7 0Ω 3 GND REF1 6 R603 4 REF2 V+ 5 NC OUT ADAPTOR CONNECTOR IBAT_SNS P+ VP C26 0.1 µF R52 C603 70 kΩ R56 1 R47 70 kΩ CONN-RMC-2PIN VP Q6 74 kΩ R53 CONVERTER OUTPUT CURRENT SENSE CSD17527Q5A R603 74 kΩ 2 QFN5X6MM 3 2N2907A R603 CONN-RMC-2PIN 2 Q8 2N2907A 5 1 VP_SNS Q9 BAT+ CONN-RMC-2PIN VADP_SNS J3 R26 U15 ADP- V3V3 1 kΩ R51 INA28xAID 4 S R603 R48 10 kΩ R55 SO8 S 10 kΩ R54 10 kΩ 1 8 BAT+ R29 VLOAD -IN +IN R34 R603 D11 10 kΩ 2 7 0Ω 1 kΩ R603 D12 3 GND REF1 6 R603 BAT54S C AC_SW REF2 V+ R603 SOT-23 BAT54S 4 5 B Q7 SOT-23 NC OUT A C MMBT2222ALT1 ILOAD_SNS A C SOT23 P- E ADP- C28 R39 0.1 µF C603 10 kΩ R603 LOAD CURRENT SENSE V3V3 V3V3 PANEL AND ADAPTOR VOLTAGE SENSE SLPA013 – October 2014 Hybrid Battery Charger With Load Control for Telecom Equipment 9 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
Schematics www.ti.com LOAD CURRENT CONTROL V3V3 LOAD_ENABLE TEMPERATURE SENSOR R6 R5 1 kΩ U1 10 kΩ R4 U2 R603 TPS25910RSA R603 R2 26 kΩ TMP709 RSA-16 20 kΩ 1 5 1 16 R603 R7 R8 SET VCC VIN1 EN 100 kΩ 200 kΩ R603 2 2 15 R603 R603 GND VLOAD VIN2 FLT 3 4 C2 3 14 OT HYST 100 nF VIN3 GND6 LOAD_ENABLE DBV_5 C603 C 4 13 GATE GND5 B 5 12 Q2 C6 R1 GND1 OUT2 Q1 8 MMBT2222ALT1 C1 K E DNP 0.1 µF 40.2 kΩ 6 11 CSD17313Q2 6 J5 SOT23 D1 + C603 R603 GND2 OUT1 SON_2X2MM 5 CONN-RMC-2PIN SMAJ20A 7 ILIM OUT 10 4 2 12 V at 4.5 A VOUT PWPD SMA 7 1 CAP_EEUCF K 8 9 1 CONN-RMC-2PIN A GND3 GND4 D2 C4 + C3 MBR130 17 0.1 µF 47 µF D_SOD123 2 3 C603 CAP_EEUCF CONN-RMC-2PIN A AGND R33 LOAD CONNECTOR 10 mΩ 2010 C5 DNP CONN-RMC-2PIN 1 BAT+ C603 VLOAD R11 U3 2 10 mΩ VP A2 TPS738xxDCQR CONN-RMC-2PIN 2010 DCQ C 1 2 V3V3 J1 IN OUT CONN-RMC-2PIN BAT+ A1 5 R9 EN GND1 6.8k D6 3 4 R603 C8 C9 BAT54C R3 GND FB 10uF 0.1uF BATTERY CONNECTOR SOT-23 C10 C7 0Ω C603 C603 6 10 µF 0.1 µF R603 C603 C603 R10 V3V3 BAT+ IBAT_SNS 4k R603 IP_SNS J4 R40 CONN-4P-TOPENTRY R18 0Ω R22 46.8 kΩ R603 47 kΩ 1 R603 V3V3 R36 U5 R603 0Ω C21 MSP430F5132IDAR R603 0.1 µF DA_38P 2 VBAT_SNS C603 1 38 ILOAD_SNS C29 2 AVCC P3.6 37 PJ.4/XOUT P3.5 VADP_SNS 2.2 nF 3 36 3 C603 4 PJ.5/XIN NMI/SBWTDIO_RST 35 S C23 5 AVSS SBWTCK/TEST 34 R19 C25 VBAT_SNS P1.0 P3.3 2.2nF 6 33 C22 4 10 kΩ 10 nF C603 7 P1.2 P3.2 32 2.2 nF R603 C603 D9 VP_SNS P1.1 PJ.6 8 31 V3V3 C603 DNP BAT54S 9 P1.3 DVCC 30 R35 SOT-23 10 P1.4 DVSS2 29 C20 470 nF 47k A C 11 P1.5 VCORE 28 C603 R603 PJ.0 P3.1 AC_SW 12 27 PJ.1 P3.0 PAN_SW ILOAD_SNS 13 26 14 PJ.2 P2.7 25 15 PJ.3 P2.6 24 P1.6 P2.5 V3V3 BUCK_PWM 16 23 R24 R41 R25 17 P1.7 P2.4 22 R23 1 kΩ SYNCB_PWM P2.0 DVSS1 0Ω 1 kΩ 18 21 V3V3 1 kΩ R603 R603 19 P2.1 DVIO 20 R603 R603 P2.2 P2.3 LOAD_ENABLE BATTERY VOLTAGE SENSE A A A AC_CHRG LOW_BAT BAT_CHRG D5 D3 D4 C30 LED CONTROLLER SECTION LED LED 2.2 nF C603 DNP K K K 10 Hybrid Battery Charger With Load Control for Telecom Equipment SLPA013 – October 2014 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
www.ti.com Test Results 6 Test Results Figure 7. Variation of the Duty Cycle from the Controller Figure 8. Seamless Transfer from Panel to Adaptor SLPA013 – October 2014 Hybrid Battery Charger With Load Control for Telecom Equipment 11 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
Test Results www.ti.com Figure 9. Output PWM Pulses from UCC27211 Figure 10. Load Switch Response to Short Circuit 12 Hybrid Battery Charger With Load Control for Telecom Equipment SLPA013 – October 2014 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
www.ti.com Test Results Figure 11. MSP430 Fast Trip Comparator Response to Load Short Circuit (EN) SLPA013 – October 2014 Hybrid Battery Charger With Load Control for Telecom Equipment 13 Submit Documentation Feedback Copyright © 2014, Texas Instruments Incorporated
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