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 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 T 2 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© 1999-2005 1 VA7205_100-1.3_En CS2/LEDT 7 4 Voltage Regulator VCC 8 Internal Reference BAT Driver Control Block 5 D 2 TS Timer Current Regulator 6 1 3 Figure 2 VA7205 Function Block Diagram Ordering Information MODEL OUTPUT VOLTAGE RECHARGING VOLTAGE PACKAGING PIN COUNT VA7205CF 4.2V 4.075V SOP 8 VA7205DF 4.2V 4.075V MSOP 8 PIN DESCRIPTION PIN NAME LEDS PIN NO. 1 I/O PIN DESCRIPTION O 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. TS 2 I VSS 3 PWR Ground BAT 4 I Battery Voltage Sense Input This pin should be tied directly to the positive side of the battery via a 300~680Ω resistor. A 10uF capacitor should be connected between battery’s positive and negative terminals. DRIVE 5 O External Pass Transistor Drive Output This output drives an external pass-transistor (PNP or P-Channel MOSFET) for current and voltage regulation. I 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). CS1 6 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. CS2/LEDT 7 I/O VCC 8 PWR Supply Voltage Connect to positive terminal of power supply. A 10uF capacitor should be connected between VCC and VSS. Absolute Maximum Rating (Unless otherwise noted) Total Power Dissipation, PD（TA＝25℃） Supply Voltage (VCC) ................................................－0.3V～＋18V SOP8 ........................................................................................... TBD CS1、CS2/LED、DRIVE、BAT、 MSOP8 ........................................................................................ TBD LEDS、TS Input Voltage ..................................－0.3V～VCC＋0.3V Storage Temperature Range......................................－65℃～150℃ Operating Ambient Temperature Range, TA ............ －40℃～＋85℃ Lead Temperature（Soldering，10 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 noted，VCC＝5V。The operating temperature for items marked with“♦”:－40℃≤TA≤85℃；The operating temperature for items marked without“♦: TA＝25℃；The temperature for typical value: TA＝25℃） PARAMETER SYMBOL Power Supply Voltage VCC Power Supply Current ISUPPLY Input Voltage Under Voltage lockout Sleep Current TEST CONDITION MIN ♦ TYP 4.5 VCC＝5V ♦ 1 VCC＝12V ♦ 2 VUVLO VCC rising ♦ ISLEEP VCC No Connect，VBAT＝ 4.2V ♦ 3.8 MAX UNIT 12 V 3 mA mA 4.07 4.3 V 7 20 μA 4.168 4.200 4.232 V 4.158 4.200 4.242 V BATTTERY VOLTAGE REGULATION Regulation Voltage VREG Line Regulation VCC＝VCS1＝VCS2/LEDT ♦ 0.05 % VREG－0.175 VREG－0.125 VREG－0.075 V VCC＝5V～12V RECHARGE Recharge Threshold VRECHG CURRENT REGULATION Current Regulation Threshold VCSREG Referenced to VCC (see note 1) ♦ 135 150 165 mV 10 18 28 mV 8 15 22 mV PRECHARGE CURRENT REGULATION Precharge Current Regulation threshold VCSPRE Referenced to VCC CHARGE TERMINATION DETECTION Charge Termination Threshold VCSTERM Referenced to VCC TEMPERATURE SENSE (VOLTAGE AT TS PIN) Lower Temperature Threshold VTS1 26 28 30 %VCC Upper Temperature VTS2 55 58 61 %VCC 3 VA7205_100-1.3_En Threshold PRECHARGE TERMINATION Rising Precharge Threshold VMIN 2.94 3.00 3.06 V 2.5 2.8 3.1 V/V BATTERY RESISTANCE CANCELLATION Battery Resistance Cancellation Gain GCOMP (see note 3） DRIVE Pull-up Resistance VBAT＝4.5V High Output Voltage VCC＝12V，VBAT＝4.5V ♦ 11.9 V Sink Current VBAT＝3.6V，VDRIVE＝1V ♦ 30 mA 5 kΩ BATTERY PACK ABNORMAL OPERATION DETECTION Battery Short Circuit Threshold VBSC 0.3 0.8 1.2 V Battery Failure Timeout tFAIL 10 15 20 min 0.3 0.5 0.75 s LEDS Output Pulse Period LEDS Output Pulse Duty Cycle 50 LEDS,CS2/LEDT Output Sink Current VLEDS=VCS2/LEDT=0.3V BAT Input Current VBAT＝3.6V BAT External Cap % 10 mA 4.2 4.7 10 μA 47 μF TS Input Current VTS＝2.5V CS1 Input Current VCS1＝4.95V，VBAT＝3.6V 5 μA CS2/LEDT Input Current VCS1＝4.95V，VBAT＝3.6V 5 μA Note: μA 0.01 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: GCOMP＝ΔVREG/(VCS2/LEDT－VCS1). 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 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 VREG IREG Regulation Voltage Regulation Current VMIN VBSC IPRECHG ITERM t<tFAIL Figure 4 Typical Charge Profile 5 VA7205_100-1.3_En Any State VCC<VBAT Sleep Mode Red LED Off Green LED Off Any State VCC>VBAT VBAT<VCC<VUVLO Low Supply Voltage Red LED Off Green LED Off VCC>VUVLO Abnormal Battery State Wait for Restart Timer>15min Red LED Blink Green LED Off VTS1<VTS<VTS2, exceeded 0.5 sec Abnormal Battery Temperature Range Charge Paused Red LED Blink Green LED Off Precharge Started Timer Red LED On (V BAT>VBSC) Red LED Blink (V BAT<VBSC) Green LED Off VBAT>VMIN VBAT<VMIN Current Regulation Charge Red LED On Green LED Off VTS<VTS1 or VTS>VTS2 exceeded 0.5 sec ICHG=IREG ICHG<IREG Voltage Regulation Charge Red LED On Green LED Off VBAT<VMIN Charge Termination ICHRG<ITERM Detect Charge Termination Recharge VBAT<VRECHG Detect Red LED Off Green LED On Figure 5 Operation State Diagram 6 VA7205_100-1.3_En 1. Qualification and Pre-charge 3. Voltage Regulation Phase The VA7205 starts a charge-cycle if any of the following situations is detected: 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. a) The power is supplied（VCC＞4.2V）, and a battery is inserted (VBAT<VRECHG); b) A battery is already present (VBAT<VREG) and power is supplied (VCC>4.2V). Charge qualification is based on battery voltage and temperature. If the battery voltage is below the pre-charge threshold VMIN, the VA7205 uses 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 5.1KΩ 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 IPRECHG＝（1＋ R9 VCSPRE ）× 5.1 R1 Where R9’s dimension is KΩ, and R9’s value should be less than 10KΩ.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. 4. Charge Termination During the Voltage Regulation Phase, the charge current gradually decreases. After the charge current decreased to ITERM＝VCSTERM/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<VTS1 or VTS>VTS2 for 0.5 seconds, it indicates that the battery temperature is too high or too low and the charge cycle is paused. When VTS recovered back to the range between VTS1 and VTS2 for more than 0.5 seconds, the charge cycle resumes. 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 VBAT＜VRECHG 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. The TS pin can be used as charge-inhibit input. The user can use a switch to inhibit charge by connecting the TS pin to VCC or VSS (or any level outside the VTS1 To VTS2 thresholds). Applying a voltage between the VTS1 and VTS2 thresholds to pin TS returns the charger to normal operation. 2. Current Regulation Phase The VA7205 has two charge indicator pin: LEDS and CS2/LEDT. After the battery voltage level reaches VMIN, the VA7205 enters the Current Regulation Phase. The charging current is set as: IREG＝VCSREG/R1. Therefore, the charging current can be set to a desired level by adjusting the external resistor (R1). 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<VBSC, or 7 6. Charge status Indication VA7205_100-1.3_En pre-charge time exceeds 15 minutes, or abnormal battery temperature in the case of VTS<VTS1 or VTS>VTS2 for at least 0.5 seconds), the LEDS pin outputs a 50% duty cycle 2Hz pulse and cause red LED to blink. Upon the charge termination, the LEDS pin will change to high impedance state and turn off the red LED. The LEDT/CS2 pin is charge-termination indicator. It can be connected to VCC via a green LED and a 330 ohm current limit resistor. During the charge process, the voltage level at LEDT/CS2 is set close to VCC and the green LED is turned off. Upon the charge termination, LEDT/CS2 is pulled low and lights up the green LED. 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. 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 There is an internal timer within the VA7205. The timer starts at the same time as the precharge stage. If precharge didn’t complete (VBAT<VMIN) within 15 minutes, then VA7205 will “think” that battery is malfunction and force the charge to stop, meanwhile, the red LED will flash to bring up user’s attention. At this time, the user must disconnect the power supply to VM7025 and then connect it back on again to start a new charge cycle. 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. 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 signal（VCS2/LEDT－VCS1）, an extra offset voltage △VREG can be added to VREG to cancel the effect of RPACK and therefore effectively reduce the charge time. 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 TL～TH, (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 RTL＞RTH, then at TL, the voltage drop across TS is: VTSL＝ R6 R TL R5 + R6 R TL ×VCC VTSH＝ R5 + R6 R TH From Fig. 3, we can get: VCS2/LEDT－VCS1＝(VCC－VCS1)×R3/(R2＋R3) ICHRG＝(VCC－VCS1)/R1 As well as, △VREG ＝GCOMP×(VCS2/LEDT－VCS1) In ideal compensating state: △VREG ＝RPACK×ICHRG At TH, the voltage drop across TS is: R6 R TH 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 3kΩ. In order to determine the value of R2 and R3, we first find the equation between R2 and R3. From above four equations, we can get: R3＝R2×RPACK/(R1×GCOMP－ RPACK) ×VCC ＝ Therefore, if we assume VTSL＝VTS2＝k2×VCC Put R1＝0.3Ω，GCOMP＝2.7into equation（5）, we have: VTSH＝VTS1＝k1×VCC The solutions are: R R (k − k 1 ) .............................. （1） R5＝ TL TH 2 (R TL − R TH )k 1k 2 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 RTH＞RTL and we can calculate: R5＝ R6＝ R2 .................................. （5） R1 × GCOMP −1 RPACK 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 ) 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 可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 R3＝ R2 0.81 −1 R PACK a) If RPACK≤0.405Ω, then R3≤R2, we can select R3 ＝ 3.3k Ω and calculate R2 from equation（5）. For example: if RPACK ＝ 0.1 Ω , then R2 ＝ 23.43kΩ, we can select a standard value of 24 k Ω. b) If RPACK＞0.405Ω, then R3＞R2, we can select R2 ＝ 3.3k Ω and calculate R3 from equation（5）. For example: if RPACK＝0.6Ω, then R3＝9.43k Ω, we can select standard value of 10 kΩ. In summary, the principle of determining R2 and R3 is: choose the smaller one of R2 and R3 in the range of 3kΩ～5kΩ, 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 3kΩ～ 5kΩ 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: VA7205_100-1.3_En RPACK＜R1×GCOMP ..................................... （6） 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, β and theta θ 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, VCC ＝ 6V and R1 ＝ 0.3 Ω , then the constant-current charging current is: IREG＝VCSREG/R1＝150mV/0.3Ω＝0.5A。 a) Selecting BVCEO At beginning of charging, the voltage drop across the collector-emitter is the largest and VCE ＝VCS1－VBAT. 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 BVCEO＞15V. 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: VCE＝VCS1－VBAT＝6－0.15－3.0＝2.85V； Collector current IC＝IREG＝0.5A。 Therefore the power dissipation PD is: PD＝VCE×IC ................................................ （7） ＝2.85×0.5＝1.425W c) Selecting thetaθJA Theta θJA is related to packaging size of the transistor. Properly selecting θ JA will keep the junction temperature below manufacturer’s recommended value TJMAX when transistor is at its maximum power dissipation. Assuming maximum junction temperature TJMAX＝150℃, at room temperature TA＝40℃, we can calculate the transistor’s maximum allowed thetaθJAMAX is: θJAMAX＝(TJMAX－TA)/ PD ............................ （8） ＝(150℃－40℃)/1.425W＝77.2℃/W Likewise, we need to select the transistor 10 whose θ JA is smaller than θ JAMAX with 10% margin. In this example, we choose a PNP transistor with theta θ 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: IC＝IREG×150% .......................................... （9） ＝0.5×150%＝0.75A e) Selectingβ We can use the maximum collector current ICMAX and its corresponding base current IB to determine the value of β. In this example, ICMAX ＝ IREG and IB is the transistor’s forcing current in VA7205.We choose IB ＝30mA, we have: B B B β＝ICMAX/IB ............................................... （10） B ＝0.5/0.03＝17 It is common for a bipolar transistor’s β larger than 17, it is easy to find a transistor that will meet the requirement for VA7205. Following steps a～e 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 θ 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 Ω 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 ＝VCC－VD1－VR1－VBAT（VD1is 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 VA7205_100-1.3_En has the largest power dissipation and the source-drain voltage is: VDS＝VCC－VD1－VR1－VBAT ＝6.5－0.7－0.15－3.0＝2.65V； Drain current ID＝IREG＝0.5A whose VGS at IREG is smaller than VGSMIN, of course, the PMOS’s threshold voltage must be smaller than VGSMIN. Likewise, following steps a～e above, we can determine the type of PMOS to choose. 5. Blocking Diode D1 Therefore PMOS transistor’s power dissipation PD is: PD＝VDS×ID .............................................. （11） ＝2.65×0.5＝1.325W c) SelectingθJA The maximum allowed thetaθJAMAX for PMOS transistor is: θJAMAX＝(TJMAX－TA)/ PD ＝(150℃－40℃)/1.325W＝83℃/W Therefore, it’s ample to select a PMOS transistor with TSSOP-8 package that has a thetaθJA 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: VGS＝VCC－(VD1＋VR1＋VDRIVE) 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－(VD1＋VR1＋VOL) ............. （12） ＝6.5－(0.7＋0.1＋1.0)＝4.65V We need to make sure we choose a PMOS 11 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. 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. VA7205_100-1.3_En Packaging Figure 6 VA7205 8-Pin SOP Mechanical Date (unit: mm unless otherwise specified) 12 VA7205_100-1.3_En Figure 8 VA7205 8-Pin MSOP Mechanical Date (unit: mm unless otherwise specified) www.vimicro.com 13 VA7205_100-1.3_En 14