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| VA7205_100-1.3_En ADVANCED LINEAR CHARGER IC For LITHIUM-ION AND LITHIUM-POLYMER Battery FEATURES Ideal for Single (4.2V) Li-ion or Li-Polymer Packs * Better Than 1% Voltage Regulation Accuracy With Preset Voltage www..com * Adjustable precharge current with an external resistor * Adjustable Charging Current During Constant Current Charging Stage * Constant Voltage Charging * Automatic Battery-Recharge Feature * Cell-Temperature Monitoring Before and During Charge * Dynamic compensation of Battery Pack's Internal Impedance to Reduce Charge Time * Charge Status Output for Dual Led * Cell Condition Monitoring * Automatic Low-Power Sleep Mode When Vcc is Removed or When Voltage Supply is Lower than battery voltage * Requires Small Number of External Components * Packaging: 8-Pin SOP or MSOP * condition the battery. The conditioning charge rate can be adjusted with an external resistor. After the battery is precharged to Vmin, the VA7205 applies a constant current to the battery. An external sense-resistor sets the current. The constant-current phase continues until the battery reaches the charge-regulation voltage (normally at 4.2V) and then the VA7205 begins the constant-voltage phase. The accuracy of the voltage regulation is better than 1% over the operating-temperature and supply-voltage ranges. Under this stage the charging current will gradually decrease. Charge stops when the current tapers to the charge termination threshold, ITERM. The VA7205 will continue monitoring the battery voltage level and entering a new cycle of charging if the battery's voltage level has fell below VRECHG (normally at VREG 125mV). During the charging process, for the safety concern, the VA7205 continuously measures battery temperature using the battery's internal heat sensitive resistor and an external resistors. If the temperature of the battery exceeds the pre-set temperature range, the charging process will come to a halt after 0.5 seconds; After the temperature fell back into the pre-set temperature range, the charging will continue again after 0.5 seconds. The VA7205 can also dynamically compensate the battery pack's internal impedance to reduce the charge time. DESCRIPTION The VA7205 series advanced Lithium-Ion (Li-Ion) and Lithium-Polymer (Li-Pol) Linear Charger ICs are designed for cost-sensitive and compact portable electronics. They combine high-accuracy current and voltage regulation, battery condition monitoring, temperature monitoring, charge termination, charge-status indication, and internal impedance compensation in a single 8-pin IC. It is the best suitable device to be used in the PDA, mobile phones, and other portable devices. The VA7205 monitors the battery charging status by detecting the battery voltage level. The VA7205 charges the battery in three phases: conditioning, constant current, and constant voltage.If the battery voltage is below the low-voltage threshold, Vmin (normally at 3V), the VA7205 precharges using a low current to LED 1 S T2 S VSS 3 BAT 4 VA7205CF Top View (Not to Scale) 8 VCC 7 CS2/LEDT 6 CS1 DRIV 5 E Figure 1 VA7205CF 8-Pin SOP FUNCTION BLOCK DIAGRAM Vimicro Copyright(c) 1999-2005 1 VA7205_100-1.3_En CS2/LEDT 7 Voltage Regulator BAT 4 Driver 5 D VCC 8 Internal Reference Control Block Timer 2 TS www..com Current Regulator 6 1 3 Figure 2 VA7205 Function Block Diagram Ordering Information MODEL VA7205CF VA7205DF OUTPUT VOLTAGE 4.2V 4.2V RECHARGING VOLTAGE 4.075V 4.075V PACKAGING SOP MSOP PIN COUNT 8 8 PIN DESCRIPTION PIN NAME PIN NO. I/O PIN DESCRIPTION Charge Status Output During the charging, this pin is pulled low to VSS. After the charging completed, this pin will be appear as high-impedance state. Under the case of abnormal battery operation or abnormal high temperature, a 50% duty-cycle 2Hz pulse will be generated. This pin can be connected to the LED diode via a 330 ohm resistor. Temperature Sense Input Input for an external battery-temperature monitoring circuit. The input voltage level for this pin has to be between VTS1 and VTS2, otherwise, VA7205 will treat as abnormal temperature range. Ground Battery Voltage Sense Input This pin should be tied directly to the positive side of the battery via a 300~680 resistor. A 10uF capacitor should be connected between battery's positive and negative terminals. External Pass Transistor Drive Output This output drives an external pass-transistor (PNP or P-Channel MOSFET) for current and voltage regulation. Current-Sense Input Battery current is sensed via the voltage developed on this pin by an external sense resistor. The external resistor can be placed between positive terminal of the power supply and the emitter (PNP transistor) or source (PMOS transistor). LEDS 1 O TS VSS BAT 2 3 4 I PWR I DRIVE 5 O CS1 6 I 2 VA7205_100-1.3_En Charge-Rate Compensation Input/charge termination status output During charging, this pin can be used for battery resistance cancellation. After the charging termination, this pin is pulled low to VSS and it can be used as a charging termination indicator. Supply Voltage Connect to positive terminal of power supply. A 10uF capacitor should be connected between VCC and VSS. CS2/LEDT 7 I/O VCC 8 PWR Absolute Maximum Rating (Unless otherwise noted) Total Power Dissipation, PDTA25 Supply Voltage (VCC) ................................................0.3V18V SOP8 ........................................................................................... TBD CS1CS2/LEDDRIVEBAT www..com MSOP8 ........................................................................................ TBD LEDSTS Input Voltage ..................................0.3VVCC0.3V Storage Temperature Range......................................65150 Operating Ambient Temperature Range, TA ............ 4085 Lead TemperatureSoldering10 seconds ........................300 Junction Temperature ...............................................................150 Note: Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond the recommended operating condition is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. Electrical Characteristics Unless otherwise notedVCC5VThe operating temperature for items marked with"":40TA85The operating temperature for items marked without": TA25The temperature for typical value: TA25 PARAMETER Power Supply Voltage Power Supply Current Input Voltage Under Voltage lockout Sleep Current SYMBOL VCC ISUPPLY VUVLO ISLEEP TEST CONDITION VCC5V VCC12V VCC rising VCC No ConnectVBAT 4.2V MIN 4.5 TYP 1 2 MAX 12 3 UNIT V mA mA 3.8 4.07 7 4.3 20 V A BATTTERY VOLTAGE REGULATION Regulation Voltage Line Regulation RECHARGE Recharge Threshold CURRENT REGULATION Current Regulation Threshold Precharge Current Regulation threshold Charge Termination Threshold Lower Temperature Threshold Upper Temperature VCSREG Referenced to VCC (see note 1) 135 150 165 mV VRECHG VREG0.175 VREG0.125 VREG0.075 V VREG VCCVCS1VCS2/LEDT VCC5V12V 4.168 4.158 4.200 4.200 0.05 4.232 4.242 V V % PRECHARGE CURRENT REGULATION VCSPRE Referenced to VCC 10 18 28 mV CHARGE TERMINATION DETECTION VCSTERM Referenced to VCC 8 15 22 mV TEMPERATURE SENSE (VOLTAGE AT TS PIN) VTS1 VTS2 26 55 28 58 30 61 %VCC %VCC 3 VA7205_100-1.3_En Threshold PRECHARGE TERMINATION Rising Precharge Threshold Battery Resistance Cancellation Gain (see note 3 VMIN 2.94 3.00 3.06 V BATTERY RESISTANCE CANCELLATION GCOMP 2.5 2.8 3.1 V/V DRIVE Pull-up Resistance www..com VBAT4.5V VCC12VVBAT4.5V VBAT3.6VVDRIVE1V 11.9 30 5 k V mA High Output Voltage Sink Current BATTERY PACK ABNORMAL OPERATION DETECTION Battery Short Circuit Threshold Battery Failure Timeout LEDS Output Pulse Period LEDS Output Pulse Duty Cycle LEDS,CS2/LEDT Output Sink Current BAT Input Current BAT External Cap TS Input Current CS1 Input Current CS2/LEDT Input Current VTS2.5V VCS14.95VVBAT3.6V VCS14.95VVBAT3.6V VLEDS=VCS2/LEDT=0.3V VBAT3.6V 4.7 0.01 5 5 10 4.2 10 47 VBSC tFAIL 0.3 10 0.3 0.8 15 0.5 50 1.2 20 0.75 V min s % mA A F A A A Note: 1. Unless otherwise noted, all voltage levels in the table are referenced to VSS. 2. Please use application circuit schematic in Figure 3 and Figure 5. 3. Definition for the Compensation Gain: GCOMPVREG/(VCS2/LEDTVCS1). FUNCTION DESCRIPTION The VA7205 is an advanced linear charge controller for single Li-Ion or Li-Pol applications . Figure 3 shows the schematic of charger using a PNP pass transistor. Figure 4 is a typical charge profile. Figure 5 shows the schematic of a charger using P-Channel MOSFET. Figure 6 is an operational state diagram. 4 VA7205_100-1.3_En www..com Figure 3 Li-ion/Li-Pol Charger Using a PNP Pass Transistor Preconditioning Phase Regulation Current Current Regulation Phase Voltage Regulation and charge Termination Phase Regulation Voltage IREG Regulation Voltage VREG Regulation Current VMIN VBSC IPRECHG ITERM t 5 VA7205_100-1.3_En www..com Any State VCC Red LED Off Green LED Off Any State VBAT Low Supply Voltage Red LED Off Green LED Off VCC>VUVLO Abnormal Battery State Wait for Restart Red LED Blink Green LED Off Timer>15min Precharge Started Timer Red LED On (V BAT>VBSC) Red LED Blink (V BAT VTS ICHG=IREG ICHG VBAT Recharge VBAT 6 VA7205_100-1.3_En 1. Qualification and Pre-charge The VA7205 starts a charge-cycle if any of the following situations is detected: a) b) The power is suppliedVCC4.2V, and a battery is inserted (VBAT 3. Voltage Regulation Phase During the Current Regulation Phase, the battery voltage level will gradually increase. When VBAT reaches VREG, the VA7205 enters Voltage Regulation Phase. During this phase, the VBAT will stop increase and stop at the VREG level, the charging current will also gradually decrease. Charge qualification is based on battery voltage and temperature. If the battery voltage is below the pre-charge threshold VMIN, the VA7205 uses www..com pre-charge to condition the battery. The conditioning charge current IPRECHG is adjustable with an external resistor R9 shown in Figure 3 and Figure 5.R9 is connected between CS1 pin and the emitter of external PNP or source of external PMOS. There is also an on-chip 5.1K resistor connected between CS1 pin and VCC. During pre-charge stage, the voltage drop between VCC and CS1 pin is VCSPRE, so the pre-charge current is set to be IPRECHG1 4. Charge Termination During the Voltage Regulation Phase, the charge current gradually decreases. After the charge current decreased to ITERMVCSTERM/R1, charge terminates and the charge current drops to zero. 5. Battery Temperature Monitoring To prevent the damage caused by the very high (or very low) temperature done to the battery pack, during the charge process, the VA7205 continuously monitors temperature by measuring the voltage in the voltage divider circuit between the battery's internal heat sensitive resistor and TS pin. The VA7205 compares the voltage at TS pin (VTS) against its internal VTS1 and VTS2 thresholds to determine if charging is allowed. If VTS R9 VCSPRE x 5.1 R1 Where R9's dimension is K, and R9's value should be less than 10K.The voltage divider is disabled if charger is not in pre-charge stage. The conditioning charge current is much smaller compared to the regulation current. This is because when battery voltage level (VBAT) is very low, a high charge current can cause safety hazard. The conditioning current also minimizes heat dissipation in the external pass-element (Q1) during the initial stage of charge. Note in scenario (a), if battery voltage level (VBAT) is greater than Recharge Threshold Voltage (VRECHG), the VA7205 will not immediately go into the charging mode. The VA7205 will wait until VBATVRECHG and then start the recharging cycle. In the scenario (b), whenever VBAT is smaller than VREG, regardless if VBAT is higher than VRECHG or not, the VA7205 will immediately enter the charging cycle until charging is complete. 6. Charge status Indication The VA7205 has two charge indicator pin: LEDS and CS2/LEDT. The LEDS pin is the charge status indicator. It can be connected to VCC via a red LED and a 330 ohm current limit resistor. During the normal operation in precharge phase, current regulation phase, and voltage regulation phase, the LEDS pin is pulled low and the red LED lights up. Under the abnormal operation (VBAT 7 VA7205_100-1.3_En pre-charge time exceeds 15 minutes, or abnormal battery temperature in the case of VTS 9. Recharge Upon the charge termination, battery voltage level (VBAT) will be same as VREG. The red LED is turned off and Green Led is turned on to indicate the charge termination. Whenever the VBAT is decreased to below the recharge threshold voltage (VRECHG), the VA7205 will automatically enter the recharge phase and light up the red LED and turn off the green LED to indicate a new charge cycle. 7. Low-Power Sleep Mode The VA7205 enters the sleep mode if the VCC fails below the voltage at the BAT input. This feature prevents draining the battery pack during the absence of VCC. When power supply is 0V, the DRIVE terminal connects to the VCC via the internal pull up resistor, therefore a conducting channel is created between PNP pass transistor's Collector and Base. This can cause a battery leakage current form to leak through this PNP pass transistor and the internal resistor. For the charger with PMOS transistor, due to the existence of the internal protection diode, the battery can dis-charging via this protection diode and the internal resistor. To prevent such kind of leakage current, a reverse bias diode (D1 refer to Figure 5) is recommended. 10. Automatic Charge-Rate Compensation In reality, due to the charge protection circuit in the Li-ion battery, there is some internal resistance (RPACK) presented in the battery pack. During the charge, the charge current can cause some voltage drop over this internal resistance. As a result, in the voltage regulation phase, the actual battery voltage is less than VREG. As the charge current decrease, VPACK decrease as well and eventually bring the battery voltage level However, due to the very close to VREG. existence of the RPACK, the battery charging time in the voltage regulation phase is considerably longer. In order to overcome the effect of the RPACK, the VA7205 provides a pin, CS2/LEDT, for battery internal resistance cancellation. By adjusting the external resistor R2 and R3 and controlling the voltage difference between CS2 signal and CS1 signalVCS2/LEDTVCS1, an extra offset voltage VREG can be added to VREG to cancel the effect of RPACK and therefore effectively reduce the charge time. 8. Indication of Abnormal Battery Operation If the battery voltage (VBAT) is lower than VBSC, the VA7205 will "think" that battery may have a short circuit problem. In this case, the red LED will blink, but the charge process continuous. If the VBAT is increased to be higher than VBSC, then red LED will stop blink and light up while continue charging. 8 VA7205_100-1.3_En Application Information 1. Selecting R5 and R6 We can determine R5 and R6 values in the application circuit according to the assumed temperature monitor range. Following is the example: Assuming temperature range is TLTH, (TL TH); the thermistor in battery has negative temperature coefficient (NTC), RTL is the resistance value at TL, RTH is the resistance value at TH, so RTLRTH, then at TL, the voltage www..com drop across TS is: VTSL R6 R TL R5 + R6 R TL Let's analyze Fig. 3, considering R2 is in parallel with LED Green, in addition, after finishing charging, R3 is in parallel with LED Green as well (R1 is very small so we can neglect its effect), therefore, both R2 and R3 cannot be too small or LED Green will be dim. Generally, we choose R2 and R3 over 3k. In order to determine the value of R2 and R3, we first find the equation between R2 and R3. From Fig. 3, we can get: VCS2/LEDTVCS1(VCCVCS1)xR3/(R2R3) ICHRG(VCCVCS1)/R1 As well as, VREG GCOMPx(VCS2/LEDTVCS1) In ideal compensating state: VREG RPACKxICHRG From above four equations, we can get: R3R2xRPACK/(R1xGCOMP RPACK) R2 .................................. 5 R1 x GCOMP -1 RPACK xVCC At TH, the voltage drop across TS is: VTSH R6 R TH R5 + R6 R TH xVCC Therefore, if we assume VTSLVTS2k2xVCC VTSHVTS1k1xVCC The solutions are: R R (k - k 1 ) .............................. 1 R5 TL TH 2 (R TL - R TH )k 1k 2 Put R10.3 COMP2.7into equation G 5 we , have: R3 R2 0.81 -1 R PACK R6 R TL R TH (k 2 - k 1 ) ..... 2 R TL (k 1 - k 1k 2 ) - R TH (k 2 - k 1k 2 ) Likewise, for positive temperature coefficient thermistor in battery, we have RTHRTL and we can calculate: R5 R TL R TH (k 2 - k 1 ) .............................. 3 (R TH - R TL )k 1k 2 R TL R TH (k 2 - k 1 ) ..... 4 R TH (k 1 - k 1k 2 ) - R TL (k 2 - k 1k 2 ) a) If RPACK0.405, then R3R2, we can select R3 3.3k and calculate R2 from equation5. For example: if RPACK 0.1 , then R2 23.43k, we can select a standard value of 24 k . b) If RPACK0.405, then R3R2, we can select R2 3.3k and calculate R3 from equation5. For example: if RPACK0.6, then R39.43k , we can select standard value of 10 k. In summary, the principle of determining R2 and R3 is: choose the smaller one of R2 and R3 in the range of 3k5k, then using equation 5 to determine the other; if there is no requirement for battery resistance cancellation, we can simply choose R3 in the range of 3k 5k while neglecting R2. From equation 5 we also know that in order , to get ideal temperature compensation effect, R1, GCOMP and RPACK need to satisfy following condition: R6 We can conclude that temperature monitor range is independent of power supply voltage VCC and it only depends on R5, R6, RTH and RT: The values of RTH and RTL can be found in related battery handbook or deduced from testing data. In actual application, if we only concern about on terminal temperature property (normally protecting overheating), there is no need to use R6 but R5. It becomes very simple to calculate R5 in this case. 2. Selecting R2 and R3 9 VA7205_100-1.3_En RPACKR1xGCOMP ..................................... 6 whose JA is smaller than JAMAX with 10% margin. In this example, we choose a PNP transistor with theta JA= 60/W in SOT223 package. d) Selecting maximum allowed current IC The maximum current conducting through the transistor is the current when charger in constant-current charging state. To leave 50% margin, in this reference design, we select following value: ICIREGx150% .......................................... 9 0.5x150%0.75A 3. Selecting PNP transistor In the process of selecting PNP bipolar transistor, we need to consider its maximum allowed current ICM, maximum allowed power dissipation PD, Collector-Emitter breakdown voltage BVCEO, and theta JA etc. We use following example to show the method of determining each of the parameters. In this example, we assume there is no blocking diode D1, VCC6V and R10.3, www..com the constant-current charging current is: then IREGVCSREG/R1150mV/0.30.5A a) Selecting BVCEO At beginning of charging, the voltage drop across the collector-emitter is the largest and VCE VCS1VBAT. At the beginning, VBAT is very small, even smaller than VBSC so VCS1 is very close to VCC. To guarantee transistor won't get damaged, there is a need to have some margin on breakdown voltage. It is generally required to have BVCEO larger than VCC. In this example, we choose BVCEO15V. b) Selecting PD Even though at the beginning of charging, the voltage drop across collector-emitter is the largest but the power dissipation isn't as the pre-charging current is small. After pre-charging finishes and it just enters into constant-current charging state, the power dissipation is at maximum for the transistor. AT this moment, the voltage drop across the collector-emitter is: VCEVCS1VBAT60.153.02.85V Collector current ICIREG0.5A Therefore the power dissipation PD is: PDVCExIC ................................................ 7 2.85x0.51.425W e) Selecting We can use the maximum collector current ICMAX and its corresponding base current IB to determine the value of . In this example, ICMAX IREG and IB is the transistor's forcing current in VA7205.We choose IB 30mA, we have: B B B ICMAX/IB ............................................... 10 B 0.5/0.0317 It is common for a bipolar transistor's larger than 17, it is easy to find a transistor that will meet the requirement for VA7205. Following steps ae above, we can select the type of transistor. 8850 with TO-92 package transistor will meet the requirement. 4. Selecting P-channel MOSFET When selecting PMOS to work with VA7205, we need to considering maximum allowed drain current ID, maximum allowed power dissipation PD, theta JA, source-drain breakdown voltage VDS and gate-source driving voltage VGS as well. The following example will demonstrate the methods of determine those parameters. In this example, blocking diode D1 exists, VCC 6.5V, R1 0.3 and constant-current charging current is IREG 0.5A a) Selecting VDS At the beginning of charging, the voltage drop across PMOS source-drain is the largest and VDS VCCVD1VR1VBATVD1is blocking diode D1's forward voltage drop at ~ 0.7V; VR1 is the voltage drop across resistor R1 and it is very small as well. Again, we require VDS is larger than VCC for this PMOS and we can select VDS 15V. b) Selecting PD For the same reason, when VA7205 just enters constant-current charging state, PMOS c) Selecting thetaJA Theta JA is related to packaging size of the transistor. Properly selecting JA will keep the junction temperature below manufacturer's recommended value TJMAX when transistor is at its maximum power dissipation. Assuming maximum junction temperature TJMAX150, at room temperature TA40, we can calculate the transistor's maximum allowed thetaJAMAX is: JAMAX(TJMAXTA)/ PD ............................ 8 (15040)/1.425W77.2/W Likewise, we need to select the transistor 10 VA7205_100-1.3_En has the largest power dissipation and the source-drain voltage is: VDSVCCVD1VR1VBAT 6.50.70.153.02.65V whose VGS at IREG is smaller than VGSMIN, of course, the PMOS's threshold voltage must be smaller than VGSMIN. Likewise, following steps ae above, we can determine the type of PMOS to choose. Drain current IDIREG0.5A Therefore PMOS transistor's power dissipation PD is: PDVDSxID .............................................. 11 2.65x0.51.325W www..comc) 5. Blocking Diode D1 The main purpose of this blocking diode D1 is to prevent battery reversing discharging at the circumstance when power supply voltage VCC is lower than battery voltage VBAT. In actual application, customer can decide whether the diode D1 is required in the specific situation. In an actual charger power supply, if diode rectifying is used (half wave or full wave), its reversing resistance is huge and battery discharging current will be very small even if VCC is zero; if switch power supply is used, in general, there is a ~3.8V Zener diode at the negative electrode of the power supply, combining with circuit resistance, the discharging current should be small as well. Therefore, customer can choose whether to use the blocking diode based on actual application circuit and its specific requirement. SelectingJA The maximum allowed thetaJAMAX for PMOS transistor is: JAMAX(TJMAXTA)/ PD (15040)/1.325W83/W Therefore, it's ample to select a PMOS transistor with TSSOP-8 package that has a thetaJA of 70/W. d) Selecting maximum allowed current ID The maximum allowed current for PMOS is same as using PNP transistor: ID 0.75A e) Gate-source driving voltage VGS Referencing Fig. 5, we can conclude that the voltage across gate-source of the PMOS is: VGSVCC(VD1VR1VDRIVE) When DRIVE terminal of VA7205 outputs low voltage VOL~ 1.0V, PMOS transistor is turned on. At same time, at constant-current charging state, VR1 is at maximum so VGS is at minimum: VGSMIN VCC(VD1VR1VOL) ............. 12 6.5(0.70.11.0)4.65V 6. PCB layout When layout PCB, R1 should be put between VCC and VA7205's CS1 pin and the connection line to R1 from both sides should be as short as possible. C1 should be placed tightly with R1 and C2 should be placed tightly with VA7205. Every effort should be made to ensure the lines between C1, R1, Q1, C2 and VA7205 as short and wide as possible. For best performance, it is suggested to minimize the area of PCB. Of course, this is also required for small form factor, reducing manufacturing cost. We need to make sure we choose a PMOS 11 VA7205_100-1.3_En Packaging www..com Figure 6 VA7205 8-Pin SOP Mechanical Date (unit: mm unless otherwise specified) 12 VA7205_100-1.3_En www..com Figure 8 VA7205 8-Pin MSOP Mechanical Date (unit: mm unless otherwise specified) www.vimicro.com 13 VA7205_100-1.3_En www..com 14 |
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