AN-9761 Fully Integrated Input Power Path Management Switch for Dual-Battery Portable System

Transcription

1 AN-976 Fully Integrated Input Power Path Management Switch for Dual-Battery Portable System Introduction As smart devices, such as smart phones and tablet PCs, are getting more powerful; battery run-time is an important constraint. An external battery case is sometimes used as an accessory to increase run time. In cases of a single larger battery capacitance, longer charging time is also a constraint. To reduce charging time, higher Constant Current (CC) is required in the battery charger. Even if high charging current is adopted; additional considerations, such as maximum power capability from AC/DC Travel Adaptor (TA) and thermal issues when a linear mode battery charger is used, are required. A dual-battery power configuration can be a simple and cost-effective approach to balance between system run-time and charging time with a given TA and charger capability. This note introduces IntelliMAX FPF3003, a fully integrated input power path management switch. It offers optimized battery charge and discharge path management and additional features in the small form factor of.6x.6mm 2 WLCSP for dual-battery portable systems. Application with FPF3003 Figure shows a typical application with FPF3003 in a portable system. Figure. Typical Application FPF3003 is a fully integrated input power path management switch located between a battery charger and PMIC or in a system with two batteries as primary and secondary power sources. It controls charge and discharge paths according to path-selection input by the system. FPF3003 also monitors the current status regarding battery presence and battery active for system power. C C2 Figure 2. Functional Block Diagram Figure 2 shows a functional block diagram. Key operation is conducted with four low-r ON P-channel MOSFETs and True Reverse Current Block (TRCB) to reduce power loss and avoid cross-conduction between two sources. Operating input voltage ranges are 2.3~5.5V at BATA (or primary and BATB) or secondary source and 4.6~5.5V at ADPIN of TA adaptor input, respectively. Internal control logic circuitry is powered by the highest voltage among ADPIN, BATA, and BATB. Typically, 30µA is consumed. Charge and discharge path switches typically have 05mΩ and 43mΩ at 3.7V, respectively, as shown in Figure 3 and Figure 4. C3 C4 202 Fairchild Semiconductor Corporation Rev /2/2

2 AN-976 A battery pack usually has an ID pin with a kω-range pulldown resistor for recognition purposes in terms of cell vendor or the battery capacitance, such as that shown in the Figure 5 schematic. FPF3003 monitors the battery presence using an internal 2.8V Low Dropout Regulator (LDO) with a MΩ resistor in series with the BATAID and BATBID pins. When a battery is inserted, the ID input goes to LOW, then the charge and discharge path switch related to the ID can operate. Figure 6 and Figure 7 shows BATA discharge switch operation according to BATAID. Figure 3. R ON vs. Supply Voltage (Discharge Path) Figure 4. R ON vs. Supply Voltage (Charge Path) In the case of maximum current capability,.5a at charge and 2.5A at discharge switch can be supported. Considering 0.5 ~ 0.7C rate of charging current, a maximum 200 ~ 3000mAh battery (each) can be adopted. Eventually, 4200 ~ 6000mAh can be used in total (with FPF3003) in the system. Design Tips Battery Presence Detection FPF3003 uses a battery ID pin detection function to confirm if a battery pack or module is installed properly. Figure 6. BATA Discharge Switch ON with BATAID = LOW (V BATA =4.2V, C OUT =0µF, R L =00Ω) Figure 5. Simplified Battery Pack Schematic Figure 7. BATA Discharge Switch OFF with BATAID = Floating (V BATA =4.2V, C OUT =0µF, R L =00Ω) ID detection offers design flexibility for off-the-shelf battery packs. There are three cases for dual-battery configuration, as shown in Figure 8, Figure 9, and Figure 0. At least (Figure 7) and (Figure 0) would require ID detection input for reliable operation. There are additional considerations for each case: In the Figure 8 and Figure 0 cases, a system reset function is needed should system lockup occur due to SW or HW error and the battery inside the system be unable to be detached physically. In the Figure 9 case; unwanted system shutdown can occur from battery removal without using ID pin. These design considerations are discussed further below. 202 Fairchild Semiconductor Corporation Rev /2/2 2

3 AN-976 Primary Battery Under-Voltage Detection FPF3003 monitors the primary battery of BATA for undervoltage condition. If under-voltage condition is confirmed, the system power source changes from BATA to valid BATB automatically. The under-voltage threshold level can be programmed with 0.8V of LOBAT and R divider (R and R2). Figure 8. Dual-Battery Configuration, BATA and BATB Inside System Figure 9. Dual-Battery Configuration, BATA and BATB Outside System Figure 0. Dual-Battery Configuration, BATA Inside and BATB Outside System System Reset FPF3003 includes a seven-second reset timer block to disconnect both battery power sources from the system via RESETB input if the system locks up due to software or hardware where the battery can t be detachable physically. A seven-second delay avoids a transient and unintended reset operation. When RESETB stays LOW for more than seven seconds, both discharge path switches are off so the system can be off as well. Figure 2. BATA Under-Voltage Level Setting 2 _ () 0.8 where BATA_LO=Low BATA threshold to set. If 3.4V of BATA is desired, R/R2=3.25. If R2 is chosen MΩ, R is 3.25MΩ. Higher R2 is recommended to reduce leakage current from BATA. Figure 3 shows battery-source change from BATA to BATB automatically due to LOBAT. When LOBAT is less than 0.8V or BATA is less than 3.4V, the system power source changes to valid BATB. LOBAT has a.3ms deglitch time to ensure BATA is in true under-voltage rather than transient battery voltage drop during GSM transmission operation. STAT is an open-drain output to show which battery is powering the system. Regarding STAT, Hi-Z, or HI means BATA is in use for the system power while LOW means BATB is in use. Figure 3.. Automatic Battery Change from LOBAT of BATA (V BATA = V BATB =4.2V, C OUT =00µF, R L =00Ω) Figure. System Reset (V BATA = V BATB =4.2V, C OUT =00µF, R L =00Ω) 202 Fairchild Semiconductor Corporation Rev /2/2 3

4 AN-976 Unwanted System Shutdown Prevention LOBAT has.3ms deglitch time, but this feature can be an issue if BATA in use is removed physically faster than ID pin removal or without using ID pin. Figure 6 shows the waveform. This can occur with a configuration of two batteries outside the system. Figure 7 and Figure 8 show transition waveforms with NFET. From Figure 7 transition time is reduced from.3ms to 360µs, but voltage drop is still significant. Figure 8 is with a larger output capacitance of 470µF. Voltage drop is reduced, but transition time is longer since the NFET is turned off slowly as the capacitance takes time to be discharged below the threshold voltage of the gate. Figure 4. BATA Removal in Use without ID Pin (V BATA =V BATB =3.7V, C OUT =22µF, I OUT =200mA) To avoid this unwanted shutdown issue, there are two solutions: use ID pin and/or the ID pin should be removed faster than BATA when a primary battery is removed. Figure 7. BATA Removal with NFET (V BATA = V BATB =3.7V, I OUT =200mA) NFET + C OUT =22µF Figure 5. BATA Removal in Use with ID Pin (V BATA =VB ATB =3.7V, C OUT =22µF, I OUT =200mA) From Figure 5, no significant voltage droop is observed when ID pin is removed first. In case the ID pin is not used or a battery without an ID pin is used, adding a small NFET between BATA and BATAID can reduce voltage drop, as shown in Figure 6. Figure 8. BATA Removal with NFET (V BATA = V BATB =3.7V, I OUT =200mA) NFET + Bigger C OUT of 470µF With two batteries outside system, the best way to avoid the significant voltage drop due to the deglitch time of LOBAT is to implement an ID pin to be removed faster than BATA. Discharge Path Selection Discharge path can be controlled by the BATSEL input. When BATSEL is LOW, the system is powered from BATA while BATSEL is HIGH then BATB provides power the system. Figure 9, Figure 20, and Figure 2 are showing actual waveforms and discharge path determination algorithm. Figure 6. NFET Between BATA and BATAID 202 Fairchild Semiconductor Corporation Rev /2/2 4

5 AN-976 Charge Path Selection Charge path can be controlled by the CHGSEL pin. When CHGSEL is LOW, BATA can be charged from the charger. When CHGSEL is HIGH, BATB can be charged from the charger. Figure 22, Figure 23, and Figure 24 show actual waveforms and charge path determination algorithm. Figure 9. Discharge Path Selection BATA BATB by BATSEL=HIGH (V BATA =4V, V BATB =4.2V, C OUT =00µF, R L =00Ω) Figure 22. BATB BATA by CHGSEL=LOW V CHGIN =4V, V BATA = V BATB = Floating with µf of Capacitor Figure 20. Discharge Path Selection BATB BATA by BATSEL=LOW (V BATA =4V, V BATB =4.2V, C OUT =00µF, R L =00Ω) Figure 23. BATA BATB by CHGSEL=HIGH V CHGIN =4V, V BATA = V BATB = Floating with µf Capacitor Figure 2. Discharge Path Selection Discharge Path Switch Selection Flow Chart (V BATA =4V, V BATB =4.2V, C OUT =00µF, R L =00Ω) Figure 24. Charge Path Switch Selection Flow Chart V CHGIN =4V, V BATA = V BATB = Floating with µf Capacitor 202 Fairchild Semiconductor Corporation Rev /2/2 5

6 AN-976 System-Level Evaluation Board FPF3003 performance can be tested with a system-level evaluation board. Figure 25 and Figure 26 show an actual board in 90mm x 70mm with battery charger and actual batteries. Its schematic is also shown in Figure 27Figure 26. Conclusion IntelliMAX FPF3003, a fully functional input power path management switch, is optimized for dual-battery portable systems for low R ON, reliable charge and discharge path control, detection, and reset features. Author Jeongil Lee, Sr. Applications Engineer with Fairchild Semiconductor Mobile Solutions Related Datasheets FPF3003 IntelliMAX Fully Functional Input Power Path Management Switch for Dual-Battery Portable Systems Figure 25. FPF3003 System-Level Board (Top Side) Figure 26. FPF3003 System-Level Board (Bottom Side) 202 Fairchild Semiconductor Corporation Rev /2/2 6

7 AN-976 P3 TP_BATBID P4 TP_BATAID P TA (5V) P8 GND P9 4.7uF/25V/X5R/0805 P TP_BATB C A2 D A U ADPIN CGHIN GND LOBAT A4 BATB C4 BATA A3 BATB C3 BATA D4 BATBID B2 CHGSEL D3 BATAID C2 BATSEL FPF3003 VOUT VOUT STAT RESETB B4 B3 B D2 JP3 R4 75k/0603 R5 75k/0603 JP2 D4 LED/0603 R 4.7k/0603 VIO 3.3V Header3T J 2 3 J2 2 3 D R 4.7k/0603 LED/0603 R2 49.9k/0603 U2 Linear Charger 0 IN OUT 2 9 D2 TMR BAT C2 R3 3 STAT CEB 8 4.7k/0603 LED/ STAT2 PGB D3 VSS ISET R4 4.7k/0603 open/0603 D5 C5 LED/0603 R2 4.7k/0603 uf/x5r/0603 PAD R6.3k/0603 uf/x5r/0603 C3 CON BAT Connector 8 2 B+ B+ 7 3 NC 6 NC NC NC 5 4 B- B- Header3T uf/x5r/ /0603 C R5 uf/x5r/0603 P2 TP_CHGIN C4 M/0603 P3 TP_LOBAT R7 3.25M/0603 R8 P5 TP_CHGSEL P7 TP_RESETB P6 JP4 TP_BATSEL JP 22uF/X5R/0805 C6 Open/20 C7 P0 R3 Sy stem Open/20 P GND CON2 BAT Connector 8 2 B+ B+ 7 3 NC 6 NC NC NC 5 4 B- B- R9 M/0603 R0 M/0603 P4 TP_BATA Figure 27. FPF3003 System-Level Evaluation Board Schematic DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION, OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein:. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. 202 Fairchild Semiconductor Corporation Rev /2/2 7