AN1088 Selecting the Right Battery System For Cost-Sensitive Portable Applications While Maintaining Excellent Quality INTRODUCTION Portable electronic devices have played an important role in a person’s daily digital life and have changed the way people live and work. Commonly seen portable electronic devices are Cellular Phone, Media Players, Digital Camera, Digital Camcorder, Handheld GPS, Digital Reader and PDA. With the emerging technologies that are available today, portable electronic designers are trying to integrate more features into thinner and smaller form-factors while maximizing the battery life. Batteries are the main power source for portable electronic devices, and selecting a right battery system for an unique application is one of the important factors in the portable electronic design process. It involves selecting a battery chemistry and charge management control circuitry. The battery life indicates the length a product can be used under portable mode. Longer battery life can simply make a portable device standout in the market automatically. This can usually be achieved by reducing system power consumption and implementing an advanced battery technology. When it comes to production, reliability, safety, low-cost and easy installation are the important elements while maintaining good quality. Each battery chemistry has its advantage over another. This application note is intended to assist portable electronic product designers and engineers in selecting the right chemistry for today’s low cost portable applications with design simplicity. The solutions are ideal for use in space-limited and cost-sensitive applications that can also accelerate the product time-to-market rate. DESCRIPTION BATTERY CHEMISTRIES There are three key attributes in a battery: 1. 2. 3. Energy Density (Size & Weight) Charge/Discharge Cycles (Life Cycle) Capacity (Operational duration without AC Adapter presence) Like the most engineering works, the key attributes do not exist in the same technology. There is always a trade-off between them. In today’s portable world, the product life cycle is very short. Thus, the battery life cycle is a minimal concern for customers and manufacturers. The operating duration, package size and overall system weight become the most important factors when selecting the battery chemistry for a portable application. TABLE 1: Chemistry Alkaline BATTERY COMPARISONS 1  E W ner ei gy gh D t( e W ns -h it En r/K y Vo er g) lu gy m D e en (W s O -h ity Vo pe r/L lta rat ) i ge ng O (V Vo pe ) lta n C ge irc u En (V) it d Vo lta g C Vo har e (V ) lta ge ge (V ) Brian Chu Microchip Technology Inc. 145 400 1.2 1.6 0.9 NA SLA 30-40 50-80 2.0 2.25 1.75 2.8 NiCd 40-80 100-150 1.2 1.3 0.9 1.6 NiMH 60-100 160-230 1.2 1.3 0.9 1.5 Li-Ion 110-130 210-320 3.6 4.2 2.8 4.2 TABLE 2: Chemistry BATTERY COMPARISONS 2  S p e e lfr M Di on sch th ar In (% g e R ter ) es n a is l ta nc e C C har (mΩ yc g le e / D ) s is D ch R is c ar at h ge e ar (m ge Ahr O .) Te pe m rat pe in g ra tu In re it i (° al C C ) os t Author: Very Low This application note shows characteristics of some popular battery chemistries for portable applications and fully integrated low cost single-cell Lithium-Ion/ Lithium Polymer battery charge management solutions. Alkaline 0.3 SLA 2-8 NiCd 15-20 3.5-300 1500 <10C -20-+60 Low References to documents that treat these subjects in more depth and breadth have been included in the “Reference” section. NiMH 20-25 10-400 800 <3C Li-Ion 6-10 50-500 1000 <2C -20-+60 High © 2007 Microchip Technology Inc. 100-300 1 0.25C -20-+55 2.5-25 50-500 <15C -20-+50 Low 0-+60 Med DS01088A-page 1 AN1088 Batteries usually occupy a considerable space and weight in today’s portable devices. The energy density for each chemistry dominates the size and weight for the battery pack. Table 1 indicates that Li-Ion (LithiumIon) has advantages in both energy density weight and energy density volume among other available battery technologies. Each battery chemistry is briefly reviewed below: Alkaline Alkaline batteries are not rechargeable, but are commonly seen as a portable power source because it’s low self-discharge rate and always ready to use off the shelf. Therefore, it is included in the Table 1 and Table 2 as reference against secondary (rechargeable) batteries. Rechargeable Alkaline batteries are available, but they are not very practical and reliable to use in a system due to its fast degradation after a few charge cycles. SLA (Sealed Lead Acid) SLA batteries are mature and inexpensive battery solutions, and have an advantage in low self discharge rate. However, it is not an ideal candidate for portable applications due to it’s low energy density, low charge/ discharge cycles and it is not environmentally friendly. NiCd (Nickel-Cadmium) NiCd batteries have the best charge/discharge cycles among rechargeable batteries (Table 1) and are good substitutes to Alkaline batteries because they employ the same basic voltage profile. NiCd batteries are required to be exercised periodically due to the memory effect. It is a very low-cost rechargeable solution because of the matured battery technology and simple charge algorithm. NiMH (Nickel-Metal Hydride) NiMH batteries are considered improved version of NiCd batteries that provide higher energy density and environmentally friendly material. Both NiMH and NiCd batteries have high self discharge rate (Table 2) and are subject to memory effect. Although NiMH and NiCd batteries share similar charge algorithm, NiMH batteries require a more complex design due to the heat that NiMH batteries generate during charging and the difficult −ΔV/Δt detection. Li-Ion (Lithium-Ion) Li-Ion batteries have advantages in high energy density, low maintenance requirement, relatively low self discharge rate, and higher voltage per cell. (Table 1 and Table 2) The major drawbacks of Li-Ion batteries are higher initial cost and aging effect. Li-Ion batteries age over time regardless of the usage. Protection DS01088A-page 2 circuitry is required for Li-Ion battery to prevent over voltage during charge cycle and under voltage during discharge cycle. Li-Polymer (Lithium Polymer) Li-Polymer batteries should be recognized as Li-Ion Polymer batteries. It is designed as an improved version of Li-Ion with flexible form-factors and very low profile. It is perfect for miniature applications, such as Bluetooth headsets or MP3 players. It has similar characteristics as Li-Ion and can be charged with same algorithm. It is a different technology compared to LiIon, but will be discussed as Li-Ion in this application note. SELECTING THE RIGHT BATTERY SYSTEM FOR COST-SENSITIVE APPLICATIONS In some high-end portable devices, the performances and compactness of batteries are the most important attributes when designers select the right battery system. Performances include battery run time, charge/discharge cycles, self discharge rate and safety. Battery run time, weight and compactness are based on the energy density and cell capacity. Most recent portable electronic devices are cost-sensitive with fashion in design. Even high-end devices will face lower cost during a manufacture cycle. Selecting the right battery system that can satisfy manufacturers and customers becomes a nightmare for designers and engineers. The battery system includes a battery pack and a charge management controller. With highly integrated charge management controller and design simplicity, the portable electronic device designers can reduce design time and speed up time to market for new product development. Based on the discussions above, NiMH and Li-Ion are the most popular battery chemistries that meet today’s portable applications. NiMH or Li-Ion? Table 3 depicts the critical metrics between Li-Ion and NiMH. TABLE 3: CRITICAL METRICS Li-Ion NiMH Nominal Voltage 3.6V 1.2V Cycle Life 1000 800 Memory Effect No Yes Cost ($/Wh) 2.5 1.3 Energy Density: Volume (Wh/L) 210-320 160-230 Energy Density: Weight (Wh/kg) 110-130 60-100 © 2007 Microchip Technology Inc. AN1088 Besides the cost, the Li-Ion batteries have significant advantages over the NiMH batteries. The 3.6V nominal voltage also makes Li-Ion a perfect supply voltage to most portable devices. Cell balancing can be an important issue when more than one battery cell is required for the system. For NiMH batteries to supply 3.6V, 3-cell NiMH is usually needed to maintain the voltage. A single-cell Li-Ion battery supplies the same voltage while taking less space and without worrying about cell balancing. No memory effect and maintenance free (e.g. no power cycling to prolong the battery’s life) also drive Li-Ion as a good candidate for portable applications. Although, NiMH has improved the memory effect issue compared to NiCd, it still could have premature termination from deceptive peaks during early charge cycle. Premature termination ends charge before a battery is fully charged. Consumers can charge Li-Ion battery operated handheld devices at any time during normal operation because the memory effect is not an issue with Li-Ion batteries. Mass production and extensive R&D from battery manufacturers have scaled down the cost between NiMH and Li-Ion batteries. This has led many portable device designers/engineers to favor Li-Ion over NiMH in many portable applications. Charge Algorithm Appropriate Charge Algorithm for the selected battery chemistry can effect the life, reliability and safety of a battery. Different chemistries have different charge profiles and different battery manufacturers have different recommendations when it comes to restoring energy (charge) back to batteries. The C-rate is the rated capacity for battery charge/discharge current. The rated capacity for a battery is the total amount of current it can produce or store. For example, 1C charge rate for a battery rated at 500 mAh is approximately 500 mA per hour. CHARGING NIMH BATTERIES Charging NiMH batteries can be simple or complicated. The simple and low cost solution is to charge batteries at a low constant current (e.g. 0.1C or 0.2C). However, it takes a long time to completely charge and can easily overcharge the NiMH batteries. A timer is usually implemented for charge termination. Minimum 10 hours is required if a battery is charged at 0.1C. Overcharge may occur without proper end of charge detection and can reduce the life of batteries (charge/ discharge cycles). −ΔV/Δt (the rate of voltage decrease) charge termination has improved the charge algorithm and allows fast charge until charge termination is reached. False voltage drop termination can happen from voltage fluctuations and noise that are caused by the charger and the battery. © 2007 Microchip Technology Inc. −ΔT/Δt (the rate of temperature decrease) charge termination may increase the design cost, but can increase the battery life cycle. To improve the battery life and maintain capacity, a combination of all methods should be applied to the charge algorithm. Figure 1 depicts the complete NiMH charge algorithm. CHARGE NIMH BATTERIES Trickle Charge Fast Charge -ΔV 0.8V Battery Voltage 0 Charge Current Charge Termination 1.0C 0.2C 0.05C 0 ΔT Δt Battery Temperature 0 Time FIGURE 1: NiMH Charge Algorithm . Stage 1: Trickle Charge - NiMH charge algorithm starts restoring energy to battery cell at 0.1C or 0.2C trickle charge until the battery reaches the minimum working voltage for fast charge. It can be either 0.8V or 0.9V per cell. Stage 2: Fast Charge - Fast charge restores the battery cell at a constant current rate of 1C. The charge efficiency has a noticeable improvement at fast charge rate compare to slow charging rate. It will continuously charge at 1C until one of the termination requirements is satisfied. Stage 3: Charge Termination - The charge cycle goes to the termination stage when either −ΔV/Δt or −ΔT/Δt is detected. A duration of small charge current (~0.05C) can fill up the battery cell to maximum capacity. Integrated solutions are available to charge NiMH batteries, but the cost is usually high and may not be very flexible to set battery voltage, −ΔV/Δt, −ΔT/Δt, charge rate and timer. With the broad range of Microchip’s PIC® microcontroller product line, the microcontroller can be sized for the job. In many applications, a microcontroller is already resident. By adding the Microchip’s analog high-speed PWM (Pulse Width Modulator) MCP1630 family, a power train can be easily added to the design.  The cost of using this solution is relatively low and can easily program all parameters compared to the total integrated solutions. DS01088A-page 3 AN1088 CHARGING LI-ION BATTERIES Unlike NiMH, the preferred charge algorithm for Lithium-Ion / Lithium-Ion Polymer batteries is a CC-CV (constant or controlled current; constant voltage) algorithm that can be broken up into four stages. Figure 2 depicts this charge algorithm. CHARGE LI-ION BATTERIES Trickle Charge Fast Charge 4.2V Battery Voltage Constant Voltage Charge Charge Termination 4.2V 2.8V 0 Charge Current 1.0C 0.1C 0.07C 0 0 Time Li-Ion Charge Algorithm . Stage 1: Trickle Charge - Trickle charge is employed to restore charge to deeply depleted cells. When the cell voltage is below approximately 2.8V, the cell is charged with a constant current of 0.1C maximum. An optional safety timer can be utilized to terminate the charge if the cell voltage has not risen above the trickle charge threshold in approximately 1 hour. Stage 2: Fast Charge - Once the cell voltage has risen above the trickle charge threshold, the charge current is raised to perform fast charging. The fast charge current should not be more than 1.0C. 1.0C is used in this example. In linear chargers, the current is often ramped-up as the cell voltage rises in order to minimize heat dissipation in the pass element. An optional safety timer can be utilized to terminate the charge if no other termination has been reached in approximately 1.5 hours from the start of the fast charge stage (with a fast charge current of 1C). Stage 3: Constant Voltage - Fast charge ends, and the Constant Voltage mode is initiated when the cell voltage reaches 4.2V. In order to maximize capacity, the voltage regulation tolerance should be better than ±1%. Stage 4: Charge Termination - Charging is typically terminated by one of two methods: minimum charge current or a timer (or a combination of the two). The minimum current approach monitors the charge current during the constant voltage stage and terminates the charge when the charge current diminishes below approximately 0.07C. The second method determines when the constant voltage stage is invoked. Charging continues for an additional two hours before being terminated. It is not recommended to continue to trickle charge Lithium-Ion batteries. DS01088A-page 4 When the cost between NiMH and Li-Ion batteries is no longer an issue, the only concern remaining is the cost to implement a charging circuit to portable devices. Advanced semiconductor technology makes it possible to provide fully integrated Li-Ion / Li-Polymer battery charge management controller in one small package with a completive price. After detailed review and consideration between NiMH and Li-Ion, the Li-Ion battery system is the most reliable solution that is chosen for the low cost portable devices. LI-ION / LI-POLYMER CHARGE MANAGEMENT SOLUTIONS Battery Temperature FIGURE 2: Charging in this manner replenishes a deeply depleted battery in roughly 165 minutes. Advanced chargers employ additional safety features. For example, charge is suspended if the cell temperature is outside a specified window, typically 0°C to 45°C.   Two complete Li-Ion / Li-Polymer battery charge management design examples that utilize Microchip’s MCP73831 and MCP73812 are proposed for designing a new low-cost portable devices or the cost of an alternative for an existing product. Example 1: Design Low-Cost Li-ion / LiPolymer Battery Charge Management With MCP73831  DEVICE OVERVIEW The MCP73831 device is a highly advanced linear charge management controller for use in space-limited and cost-sensitive applications. The MCP73831 is available in an 8-Lead, 2 mm x 3 mm DFN package or a 5-Lead, SOT-23 package. Along with its small physical size, the low number of external components required make the MCP73831 ideally suited for portable applications. For applications charging from a USB port, the MCP73831 adheres to all the specifications governing the USB power bus. The MCP73831 employs a constant-current / constantvoltage charge algorithm with selectable preconditioning and charge termination. The constant voltage regulation is fixed with four available options: 4.20V, 4.35V, 4.40V or 4.50V, to accommodate new, emerging battery charging requirements. The constant current value is set with one external resistor. The MCP73831 device limits the charge current based on die temperature during high power or high ambient conditions. This thermal regulation optimizes the charge cycle time while maintaining device reliability. Several options are available for the preconditioning threshold, preconditioning current value, charge termination value and automatic recharge threshold. © 2007 Microchip Technology Inc. AN1088 The preconditioning value and charge termination value are set as a ratio, or percentage, of the programmed constant current value. Preconditioning can be disabled. The MCP73831 is fully specified over the ambient temperature range of -40°C to +85°C. Figure 3 depicts the operational flow algorithm from charge initiation to completion and automatic recharge. VBAT < VPTH When the voltage at the VBAT pin rises above the preconditioning threshold, the MCP73831 enters the Constant-Current or Fast Charge mode. PRECONDITIONING MODE Charge Current = IPREG STAT = Low FAST CHARGE MODE Charge Current = IREG STAT = Low FAST CHARGE: CONSTANT-CURRENT MODE VBAT > VPTH VBAT < VPTH CONSTANT VOLTAGE MODE Charge Voltage = VREG STAT = Low CHARGE COMPLETE MODE No Charge Current STAT = High (MCP73831) STAT = Hi-Z (MCP73832) FIGURE 3: An internal under voltage lockout (UVLO) circuit monitors the input voltage and keeps the charger in shutdown mode until the input supply rises above the UVLO threshold. For a charge cycle to begin, all UVLO conditions must be met and a battery or output load must be present. A charge current programming resistor must be connected from PROG to VSS. If the voltage at the VBAT pin is less than the preconditioning threshold, the MCP73831 enter a preconditioning or Trickle Charge mode. The preconditioning threshold is factory set. In this mode, the MCP73831 supplies a percentage of the charge current (established with the value of the resistor connected to the PROG pin) to the battery. The percentage or ratio of the current is factory set. SHUTDOWN MODE VDD < VUVLO VDD < VBAT or PROG > 200 kW STAT = Hi-Z VBAT > VPTH CHARGE QUALIFICATION AND PRECONDITIONING TRICKLE CHARGE During the Constant-Current mode, the programmed charge current is supplied to the battery or load. The charge current is established using a single resistor from PROG to VSS. Constant-Current mode is maintained until the voltage at the VBAT pin reaches the regulation voltage, VREG. PROGRAM CURRENT REGULATION Fast charge current regulation can be set by selecting a programming resistor (RPROG) from PROG to VSS. The charge current can be calculated using the following equation: EQUATION 1: PROGRAM FAST CHARGE CURRENT 1000VI REG = ---------------R PROG Where: RPROG = kilo-ohms IREG = milliamperes MCP73831 Flowchart. © 2007 Microchip Technology Inc. DS01088A-page 5 AN1088 Charge Current (mA) CHARGE STATUS INDICATOR The charge status output of the MCP73831 has three different states: High (H), Low (L), and High-Impedance (Hi-Z). The charge status output can be used to illuminate 1, 2, or tri-color LEDs. Optionally, the charge status output can be used as an interface to a host microcontroller. 550 500 450 400 350 300 250 200 150 100 50 0 Table 4 summarize the state of the status output during a charge cycle. 2 4 6 8 10 12 14 16 18 20 TABLE 4: Charge Cycle State Programming Resistor (kΩ) FIGURE 4: IOUT vs. RPROG. Figure 4 shows the relationship between fast charge current and programming resistor. The preconditioning trickle charge current and the charge termination current are ratio metric to the fast charge current based on the selected device option. CONSTANT-VOLTAGE MODE When the voltage at the VBAT pin reaches the regulation voltage, VREG, constant voltage regulation begins. The regulation voltage is factory set to 4.2V, 4.35V, 4.40V, or 4.50V with a tolerance of ±0.75%. STATUS OUTPUT Shutdown Hi-Z No Battery Present Hi-Z Constant-Current Fast Charge L Preconditioning L Constant Voltage L Charge complete - Standby H TYPICAL APPLICATION 500 mA Li-Ion Battery Charger VIN 4.7 µF VBAT 3 4.7 µF 4 V DD CHARGE TERMINATION The charge cycle is terminated when, during ConstantVoltage mode, the average charge current diminishes below a percentage of the programmed charge current (established with the value of the resistor connected to the PROG pin). A 1 ms filter time on the termination comparator ensures that transient load conditions do not result in premature charge cycle termination. The percentage or ratio of the current is factory set. The charge current is latched off and the MCP73831 enters a Charge Complete mode. AUTOMATIC RECHARGE The MCP73831 continuously monitors the voltage at the VBAT pin in the Charge Complete mode. If the voltage drops below the recharge threshold, another charge cycle begins and current is once again supplied to the battery or load. THERMAL REGULATION AND THERMAL SHUTDOWN MCP73831 PROG 470Ω 1 STAT + Single Li-Ion - Cell 5 VSS 2 2 kΩ MCP73831 FIGURE 5: MCP73831 Typical Application Circuit. Due to the low efficiency of linear charging, the most important factors are thermal design and cost, which are a direct function of the input voltage, output current and thermal impedance between the battery charger and the ambient cooling air. The worst-case situation is when the device has transitioned from the Preconditioning mode to the Constant-Current mode. In this situation, the battery charger has to dissipate the maximum power. A trade-off must be made between the charge current, cost and thermal requirements of the charger. The MCP73831 limits the charge current based on the die temperature. The thermal regulation optimizes the charge cycle time while maintaining device reliability. The MCP73831 suspends charge if the die temperature exceeds 150°C. Charging will resume when the die temperature has cooled by approximately 10°C. DS01088A-page 6 © 2007 Microchip Technology Inc. AN1088 = the maximum input voltage IREGMAX = the maximum fast charge current VPTHMIN = the minimum transition threshold voltage 4.0 400 3.0 300 2.0 200 MCP73831-2AC/IOT VDD = 5.2V RPROG = 2 kΩ 1.0 100 0.0 0 240 VDDMAX 500 210 Where: 5.0 180 REGMAX 150 )×I 120 PTHMIN 90 –V 60 DDMAX 600 0 PowerDissipation = ( V 6.0 Charge Current (mA) POWER DISSIPATION Battery Voltage (V) EQUATION 2: TYPICAL CHARGE PROFILE 30 The power dissipation has to be considered in the worst-case. Time (minutes) EXAMPLE 1: POWER DISSIPATION EXAMPLE FIGURE 7: MCP73831 Typical Charge Profile in Thermal Regulation (1000 mAh Battery). Assume: VIN = 5V ±10% IREGMAX = 550 mA VPTHMIN = 2.7V Power Dissipation = (5.5V - 2.7V) x 550 mA = 1.54W DEVICE OVERVIEW EXTERNAL COMPONENTS The MCP73831 is stable with or without a battery load. A minimum capacitance of 4.7 µF is recommended to bypass the VBAT pin to VSS and VIN pin to VSS to maintain good AC stability in the constant-voltage mode. A single resistor between PROG pin and VSS is required to control fast charge current. Equation 1 and Figure 4 can be applied to find RPROG value. LED and RLED are required for status indicator. 525 RPROG = 2 kΩ 450 The MCP73812 Simple, Miniature Single-Cell Fully Integrated Li-Ion/Li-Polymer Charge Management Controller is designed for use in space limited and cost sensitive applications. The MCP73812 provides specific charge algorithms for single cell Li-Ion or LiPolymer battery to achieve optimal capacity in the shortest charging time possible. Along with its small physical size and the low number of external components required make the MCP73812 ideally suited for portable applications. The MCP73812 employs a constant current/constant voltage charge algorithm like MCP73831. The constant voltage regulation is fixed at 4.20V, with a tight regulation tolerance of 1%. The constant current value is set with one external resistor. The MCP73812 limits the charge current based on die temperature during high power or high ambient conditions. This thermal regulation optimizes the charge cycle time while maintaining device reliability. THERMAL REGULATION Charge Current (mA) Example 2: Design Ultra Low-Cost Li-ion / Li-Polymer Battery Charge Management With MCP73812  375 300 225 150 The MCP73812 is fully specified over the ambient temperature range of -40°C to +85°C. The MCP73812 is available in a 5-Lead, SOT-23 package. 75 155 145 135 125 115 95 105 85 75 65 55 45 35 25 0 Junction Temperature (°C) FIGURE 6: Thermal Regulation. © 2007 Microchip Technology Inc. DS01088A-page 7 AN1088 FAST CHARGE: CONSTANT-CURRENT MODE During the constant current mode, the programmed charge current is supplied to the battery or load. For the MCP73812, the charge current is established using a single resistor from PROG to VSS. The MCP73812 shares the same program method with MCP73831. The program resistor and the charge current are calculated using the Equation 1. Refer to Figure 4 for the Charge Current and Programming Resistor. SHUTDOWN MODE* VDD < VPD STANDBY MODE* CE = Low CONSTANT-VOLTAGE MODE CONSTANT CURRENT MODE Charge Current = IREG When the voltage at the VBAT pin reaches the regulation voltage, VREG, constant voltage regulation begins. The regulation voltage is factory set to 4.2V with a tolerance of ±1.0%. CHARGE TERMINATION VBAT < VREG VBAT = VREG CONSTANT VOLTAGE MODE Charge Voltage = VREG The charge cycle is terminated by removing the battery from the charger, removing input power, or driving the charge enable input (CE) to a logic low. An automatic charge termination method is not implemented. AUTOMATIC RECHARGE * Continuously Monitored FIGURE 8: MCP73812 Flowchart. CHARGE QUALIFICATION AND PRECONDITIONING TRICKLE CHARGE The MCP73812 does not employ under voltage lockout (UVLO). When the input power is applied, the input supply must rise 150 mV above the battery voltage before the MCP73812 becomes operational. The automatic power down circuit places the device in a shutdown mode if the input supply falls to within +50 mV of the battery voltage. The automatic circuit is always active. Whenever the input supply is within +50 mV of the voltage at the VBAT pin, the MCP73812 is placed in a shutdown mode. During power down condition, the battery reverse discharge current is less than 2 µA. For a charge cycle to begin, the automatic power down conditions must be met and the charge enable input must be above the input high threshold. The MCP73812 does not support preconditioning of deeply depleted cells, and it begins with fast charge once charging conditions satisfy. The MCP73812 does not support automatic recharge cycles since automatic charge termination has not been implemented. In essence, the MCP73812 is always in a charge cycle whenever the qualification parameters have been met. THERMAL REGULATION AND THERMAL SHUTDOWN The MCP73812 limits the charge current based on the die temperature. The thermal regulation optimizes the charge cycle time while maintaining device reliability. The MCP73812 suspends charge if the die temperature exceeds 150°C. Charging will resume when the die temperature has cooled by approximately 10°C. The thermal shutdown is a secondary safety feature in the event that there is a failure within the thermal regulation circuitry. TYPICAL APPLICATION 500 mA Li-Ion Battery Charger VIN 1 µF 4 V DD VBAT 3 + Single Li-Ion - Cell 1 µF 1 CE PROG 5 VSS 2 2 kW MCP73812 FIGURE 9: tion Circuit. DS01088A-page 8 MCP73812 Typical Applica- © 2007 Microchip Technology Inc. AN1088 The MCP73812 shares similar application with MCP73831, but Charge Enable (CE) is designed to replace charge status pin. A logic high enables battery charging while a logic low disables battery charging. The charge enable input is compatible with 1.8V logic. TYPICAL CHARGE PROFILE The power dissipation has to be considered in the worst case. The power dissipation for the MCP73812 is same as the MCP73831. Therefore, equation 2 will be applied for the MCP73812 power dissipation calculation. MCP73831 VS. MCP73812 EXAMPLE 2: MCP73812 shares same charge profile with MCP73831, but no available preconditioning and automatically charge termination. TABLE 5: MCP73831 VS. MCP73812 MCP73831 MCP73812 Cost Power Dissipation Example Assume: Low Ultra Low Applications Simple Simple Space Requirement Small Small VIN = 5V ±10% Voltage Reg. Accuracy ±0.75% ±1.0% IREGMAX = 500 mA Yes Yes VPTHMIN = 2.7V Programmable Current Note 1 Power Dissipation = (5.5V - 2.7V) x 500 mA = 1.4W UVLO Yes No Preconditioning Yes No End-of-Charge Control Yes No EXTERNAL COMPONENTS Charge Status Yes No The MCP73812 is stable with or without a battery load. A minimum capacitance of 1 µF is recommended to bypass the VBAT pin to VSS and VIN pin to VSS to maintain good AC stability in the constant-voltage mode. A single resistor between PROG pin and VSS is required to control fast charge current. Equation 1 and Figure 4 can be applied to find RPROG value. LED and RLED are required for status indicator. Charge Enable PIN No Yes Automatic Recharge Yes No THERMAL REGULATION Note 1: Charge Current (mA) 525 Automatic Power-Down Yes No Thermal Regulation Yes Yes Fully Integrated Yes Yes Voltage Reg. Options Note 2 Yes No RPROG = 2 kΩ 450 375 2: 300 225 150 75 155 145 135 125 115 95 105 85 75 65 55 45 35 25 0 MCP73812 family is also available in selectable Charge Current: 85 mA or 450 mA for applications charging from USB port with device number MCP73811. Refer to MCP73811/2 Data Sheet (DS22036) for detail information. MCP73831 voltage regulation is fixed with four available options: 4.20V, 4.35V, 4.40V or 4.50V. MCP73812 comes with a standard 4.20V constant voltage regulation. Junction Temperature (°C) FIGURE 10: Thermal Regulation. © 2007 Microchip Technology Inc. DS01088A-page 9 AN1088 CONCLUSION REFERENCES Li-Ion batteries are not only good NiMH and NiCd batteries substitutes for advanced portable electric devices, but also for cost-sensitive designs. Although, high capacity, compact size, light weight and maximum charge/discharge cycles do not exist in the same package; there is always a trade-off when engineers/ designers select the key factors for the design. Due to the phase out rate of today’s portable electric products, charge/discharge cycles is always the first to be eliminated. The aging issue of Li-Ion batteries are often ignored and rarely recommended to customers for the same reason.  “Lithium Batteries”, Gholam-Abbas Nazri and Gianfranco Pistoia Eds.; Kluwer Academic Publishers, 2004.  “Handbook of Batteries, Third Edition”, David Linden, Thomas B. Reddy; McGraw Hill Inc, 2002.  ”Batteries in a Portable World Second Edition”, Isidor Buchmann; Cadex Electronics Inc., 2000.  “Portable Electronics Product Design and Development”, Bert Haskell; McGraw Hill, 2004.  “Brief of Li-Polymer Battery’s Research and Development”, W.T. Wen; Taiwan National Science Cuncil Monthly No.7, 2001.  AN960, “New Components and Design Methods Bring Intelligence to Battery Charger Applications”, Terry Cleveland and Catherine Vannicola; Microchip Technology Inc., DS00960, 2004.  AN947, “Power Management in Portable Applications: Charging Lithium-Ion/Lithium-Polymer Batteries”, Scott Dearborn; Microchip Technology Inc., DS00947, 2004.  Microchip RTC Training Class: “Portable Power Management”, Microchip Technology Inc., 2006.  MCP73811/2 Data Sheet, “Simple, Miniature Single-Cell, Fully Integrated Li-Ion/Li-Polymer Charge Management Controllers”, Microchip Technology Inc., DS22036, 2007.  MCP73831/2 Data Sheet, “Miniature SingleCell, Fully Integrated Li-Ion/Li-Polymer Charge Management Controllers”, Microchip Technology Inc., DS21984, 2006. Selecting the right charge management controller can improve the product performance, reduce design time, simplify design cycle and optimize cost performance. The MCP73831 is a good solution to meet all of the above needs. For systems that do not require many features and are designed on a tight budget, the MCP73812 is the right candidate to perform well in battery charging applications. DS01088A-page 10 © 2007 Microchip Technology Inc. Note the following details of the code protection feature on Microchip devices: • Microchip products meet the specification contained in their particular Microchip Data Sheet. • Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the intended manner and under normal conditions. • There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data Sheets. Most likely, the person doing so is engaged in theft of intellectual property. • Microchip is willing to work with the customer who is concerned about the integrity of their code. • Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as “unbreakable.” Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act. Information contained in this publication regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer’s risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights. Trademarks The Microchip name and logo, the Microchip logo, Accuron, dsPIC, KEELOQ, KEELOQ logo, microID, MPLAB, PIC, PICmicro, PICSTART, PRO MATE, PowerSmart, rfPIC, and SmartShunt are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. AmpLab, FilterLab, Linear Active Thermistor, Migratable Memory, MXDEV, MXLAB, PS logo, SEEVAL, SmartSensor and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. Analog-for-the-Digital Age, Application Maestro, CodeGuard, dsPICDEM, dsPICDEM.net, dsPICworks, ECAN, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP, ICEPIC, Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB, MPLINK, PICkit, PICDEM, PICDEM.net, PICLAB, PICtail, PowerCal, PowerInfo, PowerMate, PowerTool, REAL ICE, rfLAB, rfPICDEM, Select Mode, Smart Serial, SmartTel, Total Endurance, UNI/O, WiperLock and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. SQTP is a service mark of Microchip Technology Incorporated in the U.S.A. All other trademarks mentioned herein are property of their respective companies. © 2007, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. Microchip received ISO/TS-16949:2002 certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona, Gresham, Oregon and Mountain View, California. The Company’s quality system processes and procedures are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and analog products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001:2000 certified. © 2007 Microchip Technology Inc. DS01088A-page 11 WORLDWIDE SALES AND SERVICE AMERICAS ASIA/PACIFIC ASIA/PACIFIC EUROPE Corporate Office 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7200 Fax: 480-792-7277 Technical Support: http://support.microchip.com Web Address: www.microchip.com Asia Pacific Office Suites 3707-14, 37th Floor Tower 6, The Gateway Habour City, Kowloon Hong Kong Tel: 852-2401-1200 Fax: 852-2401-3431 India - Bangalore Tel: 91-80-4182-8400 Fax: 91-80-4182-8422 India - New Delhi Tel: 91-11-4160-8631 Fax: 91-11-4160-8632 Austria - Wels Tel: 43-7242-2244-39 Fax: 43-7242-2244-393 Denmark - Copenhagen Tel: 45-4450-2828 Fax: 45-4485-2829 India - Pune Tel: 91-20-2566-1512 Fax: 91-20-2566-1513 France - Paris Tel: 33-1-69-53-63-20 Fax: 33-1-69-30-90-79 Japan - Yokohama Tel: 81-45-471- 6166 Fax: 81-45-471-6122 Germany - Munich Tel: 49-89-627-144-0 Fax: 49-89-627-144-44 Atlanta Duluth, GA Tel: 678-957-9614 Fax: 678-957-1455 Boston Westborough, MA Tel: 774-760-0087 Fax: 774-760-0088 Chicago Itasca, IL Tel: 630-285-0071 Fax: 630-285-0075 Dallas Addison, TX Tel: 972-818-7423 Fax: 972-818-2924 Detroit Farmington Hills, MI Tel: 248-538-2250 Fax: 248-538-2260 Kokomo Kokomo, IN Tel: 765-864-8360 Fax: 765-864-8387 Los Angeles Mission Viejo, CA Tel: 949-462-9523 Fax: 949-462-9608 Santa Clara Santa Clara, CA Tel: 408-961-6444 Fax: 408-961-6445 Toronto Mississauga, Ontario, Canada Tel: 905-673-0699 Fax: 905-673-6509 Australia - Sydney Tel: 61-2-9868-6733 Fax: 61-2-9868-6755 China - Beijing Tel: 86-10-8528-2100 Fax: 86-10-8528-2104 China - Chengdu Tel: 86-28-8665-5511 Fax: 86-28-8665-7889 Korea - Gumi Tel: 82-54-473-4301 Fax: 82-54-473-4302 China - Fuzhou Tel: 86-591-8750-3506 Fax: 86-591-8750-3521 Korea - Seoul Tel: 82-2-554-7200 Fax: 82-2-558-5932 or 82-2-558-5934 China - Hong Kong SAR Tel: 852-2401-1200 Fax: 852-2401-3431 Malaysia - Penang Tel: 60-4-646-8870 Fax: 60-4-646-5086 China - Qingdao Tel: 86-532-8502-7355 Fax: 86-532-8502-7205 Philippines - Manila Tel: 63-2-634-9065 Fax: 63-2-634-9069 China - Shanghai Tel: 86-21-5407-5533 Fax: 86-21-5407-5066 Singapore Tel: 65-6334-8870 Fax: 65-6334-8850 China - Shenyang Tel: 86-24-2334-2829 Fax: 86-24-2334-2393 Taiwan - Hsin Chu Tel: 886-3-572-9526 Fax: 886-3-572-6459 China - Shenzhen Tel: 86-755-8203-2660 Fax: 86-755-8203-1760 Taiwan - Kaohsiung Tel: 886-7-536-4818 Fax: 886-7-536-4803 China - Shunde Tel: 86-757-2839-5507 Fax: 86-757-2839-5571 Taiwan - Taipei Tel: 886-2-2500-6610 Fax: 886-2-2508-0102 China - Wuhan Tel: 86-27-5980-5300 Fax: 86-27-5980-5118 Thailand - Bangkok Tel: 66-2-694-1351 Fax: 66-2-694-1350 Italy - Milan Tel: 39-0331-742611 Fax: 39-0331-466781 Netherlands - Drunen Tel: 31-416-690399 Fax: 31-416-690340 Spain - Madrid Tel: 34-91-708-08-90 Fax: 34-91-708-08-91 UK - Wokingham Tel: 44-118-921-5869 Fax: 44-118-921-5820 China - Xian Tel: 86-29-8833-7250 Fax: 86-29-8833-7256 12/08/06 DS01088A-page 12 © 2006 Microchip Technology Inc.