L6924U USB compatible battery charger system with integrated power switch for Li-Ion/Li-Polymer Features ■ Fully integrated solution, with power MOSFET, reverse blocking diode, sense resistor, and thermal protection ■ Charges single-cell Li-Ion batteries from selectable AC adapter or USB input ■ Programmable charge current up to 1 A in AC adapter mode ■ Programmable charging current in USB mode for both high power and low power inputs ■ 4.
Contents L6924U Contents 1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Electrical characteristics .
L6924U Contents 9.3 Layout guidelines and demonstration board . . . . . . . . . . . . . . . . . . . . . . . 28 10 Application idea: dual input management with AC priority . . . . . . . . 31 11 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Description 1 L6924U Description The L6924U is a fully monolithic battery charger that safely charges single-cell LiIon/Polymer battery from either an USB power source or an AC adapter. In USB mode, the L6924U supports both low power and high power mode. Alternatively the device can charge from an AC wall adapter. The ideal solution for space-limited portable products integrates the power MOSFET, reverse blocking diode, sense resistor and thermal protection into a compact VFQFPN16 package.
L6924U 2 Pin description Pin description Figure 3. 2.1 Pin connection (top view) Pin description Table 2. Pin functions Pin I/O Name 1 I VIN 2 I VINSNS 3-4 O Pin description Input pin of the power stage. Supply voltage pin of the signal circuitry. The operating input voltage ranges from 2.5 V to 12 V, and the start-up threshold is 4 V. ST2-ST1 Open-collector status pins. 5 I TPRG Maximum charging time program pin.
Pin description L6924U Table 2. Pin I/O Name Pin description 9 I ISEL Switches between high power USB (IUSB up to 500 mA) and low power USB (IUSB/5) in USB mode. A low level sets the L6924U in low power mode and a high level sets the L6924U in high power mode. When the AC mode is selected, the ISEL pin must be connected to ground or left floating. 10 I VOSNS Output voltage sense pin. It senses the battery voltage to control the voltage regulation loop. 11 O VOUT Output pin.
L6924U 3 Maximum ratings Maximum ratings Stressing the device above the rating listed in the “absolute maximum ratings” table may cause permanent damage to the device. These are stress ratings only and operation of the device at these or any other conditions above those indicated in the operating sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Electrical characteristics 4 L6924U Electrical characteristics TJ = 25 °C, VIN = 5 V, unless otherwise specified. Table 5. Symbol VIN (1) IIN (1) Electrical characteristics Parameter Test condition Operating input voltage Min. Typ. 2.5 Start up threshold Supply current ISINK Current flowing from VOUT VOUT (1) Battery regulated voltage Max. Unit 12 V 4.1 V Charging mode (RPRG = 24 kΩ) 1.8 2.
L6924U Table 5. Electrical characteristics Electrical characteristics (continued) Symbol RDS(on) Parameter Power MOSFET resistance (3) Test condition Min. Charge current = 500 mA Typ. Max. Unit 280 380 mΩ NTC pin hot threshold voltage 10 12.5 15 %VREF NTC pin cold threshold voltage 40 50 60 %VREF TH 1. TJ from -40 °C to 125 °C 2. Guaranteed by design 3.
Block diagram 5 L6924U Block diagram Figure 4. Block diagram Logic Logic I FAULT I DETECT VIN VOUT POWER MOS VINS Logic UVLO Gas Gauge BODY CONTROL SD Mos Driver Logic ANALOG PRE. IEND VDD VDD VOSNS Logic VREF VBG Charge Control BG Logic 4.2V CA-VA-TA REG THERMAL CONTROL ISEL MODE VREF IAC VPRE IUSB LOGIC VDD VREF NTC/PTC MANAG.
L6924U 6 Operation description Operation description The L6924U is a fully integrated battery charger that allows a very compact battery management system for space limited applications. It integrates in a small package all the power elements: power MOSFET, reverse blocking diode and the sense resistor. It normally works as a linear charger when powered from an external voltage regulated adapter or USB port. However, thanks to its very low minimum input voltage (down to 2.
Operation description Figure 5. L6924U Li-Ion charging profile 0.500 4.500 0.450 4.000 0.400 Ichg (A) Ichg 3.000 Vbatt 0.300 2.500 Vbatt (V) 3.500 0.350 0.250 2.000 0.200 1.500 0.150 1.000 0.100 0.500 0.050 0.000 0.000 0 200 400 600 800 1000 1200 Charging time (sec) 6.1 Linear mode When operating in linear mode, the device works in a way similar to a linear regulator with a constant current limit protection.
L6924U Operation description Figure 6. Typical charge curves in linear mode Pre-Charge Phase V ADP V OPRGTH Fast-Charge Phase Voltage-Regulation Phase End Charge Adapter Voltage Battery Voltage V PRETH I CHG Charge Current I PRETH Power dissipation The worst case in power dissipation occurs when the device starts the fast-charge phase. In fact, the battery voltage is at its minimum value.
Operation description 6.2 L6924U Quasi-pulse mode The quasi-pulse mode can be used when the system can rely on the current limit of the upstream adapter to charge the battery. In this case, the fast charge current must be set higher than the current limit of the adapter. In this mode, the L6924U charges the battery with the same three phases as in Linear Mode, but the power dissipation is greatly reduced as shown in Figure 7. Figure 7.
L6924U Operation description Where ΔVMOS is given by: Equation 3 ΔV MOS = R DS( ON) × I LIM Where, ILIM = current limit of the wall adapter, and RDS(on) = resistance of the power MOSFET. The difference between the programmed charge current and the adapter limit should be high enough to minimize the RDS(on) value (and the power dissipation). This makes the control loop completely unbalanced and the power element is fully turned on.
Operation description L6924U Equation 5 PDIS = (VADP − VBAT ) × ILIM In conclusion, the advantage of the linear charging approach is that the designer has direct control of the charge current, and consequently the application can be very simple. The drawback is the high power dissipation. The advantage of the quasi-pulse charging method is that the power dissipated is dramatically reduced. The drawback is that a dedicated upstream adapter is required.
L6924U 7 Applications information: charging process Applications information: charging process Figure 9. 7.1 Charging process flow chart Pre-charge phase The L6924U allows pre-charging the battery with a low current when the battery is deeply discharged.
Applications information: charging process L6924U The battery is considered deeply discharged when its voltage is lower than a threshold (VPRETH), internally set to 3 V. During the pre-charge phase, the current (IPRECH) has a default value equal to 10 % of the fast-charge current. A safety timer is also present. If the battery voltage does not rise over VPRETH within this time, a fault is given (Chapter 7.7: Maximum charging time on page 21).
L6924U Applications information: charging process Equation 6 ⎛V ⎞ R AC = ⎜⎜ BG ⎟⎟ ⋅ K PRG ⎝ IAC ⎠ Where VBG is the internal reference equal to 1.23 V, whereas KPRG is a constant equal to 9500. Figure 11. IAC pin connection In USB mode (MODE pin high), the RUSB resistor can be selected as: Equation 7 ⎛V ⎞ RUSB = ⎜⎜ BG ⎟⎟ ⋅ KPRG ⎝ IUSB ⎠ Where VBG and KPRG have the same meaning and value above mentioned. The charge current in USB mode depends on RUSB as well as the state of the ISEL pin.
Applications information: charging process 7.4 L6924U End-of-charge current When the charge voltage approaches the battery regulated voltage (internally set to 4.2 V), the voltage regulation phase takes place. The charge current starts to decrease until it goes below a programmable termination current, IENDTH.
L6924U 7.5 Applications information: charging process Recharge flow chart Figure 14. Recharge flow chart 7.6 Recharge threshold When, from an end-of-charge condition, the battery voltage goes below the recharging threshold (VRCH), the device goes back in charging state. The value of the recharge threshold is 4.05 V. 7.
Applications information: charging process L6924U Figure 15. TPRG pin connection Where, RPRG = resistor which sets the current (RUSB or RAC) VREF = 1.8 V, KT = 279 x 105, VBG = 1.23 V, and TMAXCH is the charging time given in seconds. If the battery does not reach the end-of-charge condition before the timer expires, a fault is issued.
L6924U 8 Application information: monitoring and protection Application information: monitoring and protection The L6924U uses a VFQFPN (3 x 3 mm) 16-pin package with an exposed pad that allows the user to have a compact application and good thermal behavior at the same time. The L6924U has a low thermal resistance because of the exposed pad (approximately 75 °C/W, depending on the board characteristics).
Application information: monitoring and protection L6924U When the voltage (and thus, the temperature), returns to the window range, the device restarts the charging process. Moreover, there is a hysteresis for both the upper and lower thresholds, as shown in Figure 18. Figure 17. Battery temperature control flow chart Note: TBAT = OK when the battery temperature is between 0 °C and 50 °C Figure 18.
L6924U Application information: monitoring and protection charge the battery, only when the voltage at the TH pin goes under VMINTH_HYS = 780 mV (typ). For what concerns the high temperature limit, when the TH pin voltage falls under the VMAXTH = 12.5 % of VREF (225 mV Typ.), the L6924U stops the charge until the TH pin voltage reaches the VMAXTH_HYS = 248 mV (typ.). When the battery is at the low temperature limit, the TH pin voltage is 900 mV.
Application information: monitoring and protection L6924U Based on Equation 14 and Equation 17, it derives that: Equation 18 RNTC 0°C =7 RNTC 50°C The temperature hysteresis can be estimated by the equation: Equation 19 THYS = VTH − VTH _ HYS VTH × NTCT Where VTH is the pin voltage threshold on the rising edge, VTH_HYS is the pin voltage threshold on the falling edge, and NTCT (- %/°C) is the negative temperature coefficient of the NTC at temperature (T) expressed in % resistance change per °C.
L6924U 8.2 Application information: monitoring and protection Battery absence detection This feature provides a battery absent detection scheme to detect the removal or the insertion of the battery. If the battery is removed, the charge current falls below the IENDTH. At the end of the de-glitch time, a detection current IDETECT, equal to 1 mA, is sunk from the output for a time of TDETECT. The device checks the voltage at the output.
Application information: monitoring and protection L6924U Figure 21. ST1 and ST2 connection with LEDs or microcontroller Table 6. Status LEDs Indications Charge condition Charge in progress Charge done Stand by mode Bad battery temperature Battery absent Over time 8.
L6924U Additional applications information 9 Additional applications information 9.1 Selecting the input capacitor In most applications, a 1 µF ceramic capacitor, placed close to the VIN and VINSN pins can be used to filter the high frequency noise. 9.2 Selecting the output capacitor Typically, a 4.7 µF ceramic capacitor placed close to the VOUT and VOUTSN pin is enough to keep voltage control loop stable.
Additional applications information L6924U Figure 22. Thermal image of the demonstration board The VOSNS pin can be used as a remote sense; it should be therefore connected as closely as possible to the battery. The demonstration board layout and schematic are shown in Figure 23, Figure 24 and Figure 25. Figure 23. Demonstration board layout, top side Figure 24.
L6924U Additional applications information Figure 25. Demonstration board schematic Table 7. Demonstration board components description Name Value Description R1 24 kΩ AC mode fast-charge current resistor. Used to set the charging current in AC mode. R2 24 kΩ USB mode fast-charge current resistor. Used to set the charging current in USB mode. R3 3.3 kΩ End of Charge current resistor. Used to set the termination current and, as a “gas gauge” when measuring the voltage across on it.
Application idea: dual input management with AC priority 10 L6924U Application idea: dual input management with AC priority In some applications both AC adapter and USB power source may be available. Figure 26 shows a possible schematic which provides the possibility to manage two power sources (AC/USB) and gives the priority to AC adapter in case both sources are available at the same time. For simplicity, only the relevant pins of the L6924U for this application have been indicated.
L6924U Application idea: dual input management with AC priority Figure 26.
Package mechanical data 11 L6924U Package mechanical data In order to meet environmental requirements, ST offers these devices in different grades of ECOPACK® packages, depending on their level of environmental compliance. ECOPACK® specifications, grade definitions and product status are available at: www.st.com. ECOPACK® is an ST trademark.
L6924U Package mechanical data Table 8. VFQFPN16 (3 x 3 mm.) mechanical data mm. Dim. Min. Typ. Max. 0.80 0.90 1.00 A1 0.02 0.05 A2 0.65 1.00 A3 0.20 A b 0.18 0.25 0.30 D 2.85 3.00 3.15 D2 1.45 1.60 1.75 E 2.85 3.00 3.15 E2 1.45 1.60 1.75 e 0.45 0.50 0.55 L 0.30 0.40 0.50 Figure 27.
Revision history 12 L6924U Revision history Table 9. 36/37 Document revision history Date Revision Changes 20-May-2008 1 First release 22-Sep-2010 2 Modified: Table 8 and Figure 27 on page 35. Minor changes.
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