L6924D Battery charger system with integrated power switch for Li-Ion/Li-Polymer Features ■ Fully integrated solution, with a power MOSFET, reverse blocking diode, sense resistor, and thermal protection ■ Ideal for coke and graphite anode single-cell LIION packs ■ Both linear and quasi-pulse operation ■ Closed loop thermal control ■ USB BUS-compatible ■ Programmable charge current up to 1 A ■ Programmable pre-charge current ■ Programmable end-of-charge current ■ Programmable pre-charge volt
Contents L6924D Contents 1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . 4 2.1 3 4 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1 Absolute maximum ratings . . . . . . . . . . .
L6924D Contents 8.4 9 10 Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Additional applications information . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.1 Selecting the input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.2 Selecting the output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.3 Layout guidelines and demonstration board description . . .
Description 1 L6924D Description The L6924D is a fully monolithic battery charger dedicated to single-cell Li-Ion/Polymer battery packs. It is the ideal solution for space-limited applications, like PDAs, handheld equipment, cellular phones, and digital cameras. It integrates all of the power elements (the power MOSFET, reverse blocking diode and the sense resistor) in a small VFQFPN16 (3 x 3 mm) package.
L6924D 2 Pins description and connection diagrams Pins description and connection diagrams Figure 3. Pins connection (top view) IPRE IPRG VPRE IEND V VIN VREF INSNS VOUT ST2 VOSNS ST1 V TPRG GND SD 2.1 Pin description Table 2. Pin functions OPRG TH Pin I/O Name Pin description 1 I VIN 2 I VINSNS 3-4 O 5 I TPRG Maximum charging time program pin. It must be connected with a capacitor to GND to fix the maximum charging time, see Chapter 7.
Pins description and connection diagrams Table 2. 12 13 O I/O L6924D Pin functions VREF External reference voltage pin.(reference voltage is 1.8 V±2%) IEND Charge termination pin. A resistor connected from this pin to GND fixes the charge termination current threshold IENDTH: if I < IENDTH, the charger behaves according to the VPRE status (see Chapter 7.5: End-of-charge current on page 19). The voltage across the resistor is proportional to the current delivered to the battery (Gas Gauge function).
L6924D 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. 3.1 Absolute maximum ratings Table 3.
Electrical specifications L6924D 4 Electrical specifications 4.1 Electrical characteristics TJ = 25 °C, VIN = 5 V, unless otherwise specified. Table 5. Symbol VIN(1) IIN(1) Electrical characteristics Parameter Operating input voltage Min Typ 2.5 Start up threshold Supply current ISINK Current flowing from VOUT VOUT(1) Battery regulated voltage ICHG Test condition Charge current Max Unit 12 V 4.1 V Charging mode (RPRG = 24kΩ) 1.8 2.
L6924D Table 5. Electrical specifications Electrical characteristics (continued) Symbol Parameter Test condition NTC pin hot threshold voltage Min Typ Max Unit 10.625 12.5 14.375 %VREF TH NTC pin cold threshold voltage 45 50 55 %VREF 1. TJ from –40°C to 125°C. 2. Guaranteed by design.
Block diagram 5 Block diagram Figure 4.
L6924D 6 Operation description Operation description The L6924D 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. However, thanks to its very low minimum input voltage (down to 2.
Operation description L6924D When the VPRE pin is not used to program the Pre-Charge voltage threshold, it has two different functions: ● If the voltage across VPRE pin is lower than 0.8 V, when I < IENDTH, the end of charge is notified by the status pin, but the charging process is not disabled. The charge process ends when the maximum charging time expires. ● If the voltage at VPRE pin false under 0.5 V the timer is reset on the falling edge.
L6924D Operation description charging process is usually terminated when the charging current reaches a set value or when a charging timer expires (Chapter 7.9 on page 22). Figure 6 shows the different phases. Figure 6.
Operation description 6.2 L6924D 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, ICHG must be set higher than the current limit of the adapter. In this mode, the L6924D 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.
L6924D Operation description Where, ILIM = current limit of the wall adapter, and RDS(on) = resistance of the power MOSFET. The difference between the set 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. Figure 8 shows the RDS(on) values for different output voltage and charging currents for an adapter current limit of 500 mA. Figure 8.
Applications information: charging process 7 Applications information: charging process 7.1 Charging process flow chart Figure 9.
L6924D 7.2 Applications information: charging process Pre-charge current The L6924D allows pre-charging the battery with a low current when the battery voltage is lower than a specified threshold (VPRETH). The Pre-charge current has a default value equal to 10% of the fast-charge current. However it can be adjusted by connecting a resistor from the IPRE pin to GND or VREF (see Figure 10). When the resistor is connected between IPRE pin and GND, the current is higher than the default value.
Applications information: charging process L6924D Equation 8 ⎛ VPRETH RVPRE = RPRG × ⎜ ⎜V ⎝ PRETHDefault ⎞ ⎟ ⎟ ⎠ Figure 12. VPRE pin connection VPRE L6924D RPRE Where RVPRE is the resistor between VPRE and GND, and RPRG is the resistor used to set the charge current (see Section 7.4: Fast charge current), and VPRETH is the selected threshold. A safety timer is also present. If the battery voltage doesn't rise over VPRETH, before this time is expired, a fault is given (see Section 7.
L6924D 7.5 Applications information: charging process End-of-charge current When the charge voltage approaches the selected value (4.1 V or 4.2 V), the voltage regulation phase takes place. The charge current starts to decrease until it goes lower than a programmable end value, IENDTH, depending on an external resistor connected between the IEND pin and GND (see Figure 14). The equation that describes this relation as follows: Equation 10 ⎛ KEND REND = VMIN × ⎜⎜ ⎝ I ENDTH ⎞ ⎟⎟ ⎠ Figure 14.
Applications information: charging process 7.6 L6924D Recharge flow chart Figure 15.
L6924D Applications information: charging process Figure 16. TPRG pin connection TPRG L6924D CTPRG Where, VREF = 1.8V, KT = 279 x 105, VBG = 1.23V, 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.
Applications information: charging process 7.9 L6924D Termination modes Figure 17. Charge termination flow chart As shown in Figure 14, it is possible to set an end of charge current IENDTH connecting a resistor between the IEND pin and GND. When the charge current goes down to this value, after a de-glitch time, the status pins notify that the charge process is complete.
L6924D 8 Application information: monitoring and protection Application information: monitoring and protection The L6924D uses a VFQFPN 3 mm 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 L6924D has a low thermal resistance because of the exposed pad (approximately 75°C/W, depending on the board characteristics).
Application information: monitoring and protection L6924D 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 20. Figure 19. Battery temperature control flow chart Note: TBAT = OK when the battery temperature between 0°C and 50°C Figure 20.
L6924D Application information: monitoring and protection When the TH pin voltage rises and exceeds the VMINTH = 50% of VREF (900 mV typ), the L6924D stops the charge, and indicates a fault by the status pins. The device re-starts to 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.
Application information: monitoring and protection L6924D Based on Equation 16: and Equation 19: , it derives that: Equation 20 RNTC 0°C =7 RNTC 50°C The temperature hysteresis can be estimated by the equation: Equation 21 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.
L6924D 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 L6924D Figure 23. ST1 and ST2 connection with LEDs or microcontroller Table 6.
L6924D Application information: monitoring and protection Figure 24. Shutdown SD pin voltage device disabled 2V SDTH,high 0.
Additional applications information L6924D 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, 1 µF ceramic capacitor placed close to the VOUT and VOUTSN pin is enough to keep voltage control loop stable. This ensures proper operation of battery absent detection in removable battery pack applications.
L6924D Additional applications information Figure 25. 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 26, Figure 27 and Figure 28. Figure 26. Demonstration board layout, top side Figure 27.
Additional applications information L6924D Figure 28.
L6924D Additional applications information Table 7. Demonstration board components description Name Value R1 1k Pull up resistor. To be used when the ST1 is connected to a LED. R2 1k Pull up resistor. To be used when the ST1 is connected to a LED. R3 1k Pull up resistor. Connected between VREF and TH pin. R4 3k3 End of charge current resistor. Used to set the termination current and, as a “Gas Gauge” when measuring the voltage across on it. R5 24k Fast-charge current resistor.
Application ideas L6924D 10 Application ideas 10.1 USB battery charger With a voltage range between 4.75 V and 5.25 V, and a maximum current up to 500 mA, the USB power bus is an ideal source for charging a single-cell Li-Ion battery. Since it is not possible to rely on the USB current limit to charge the battery, a linear approach must be adopted. Therefore, it is only necessary to set the ICHG with a maximum value lower than 500 mA, and the device will charge the battery in Linear mode.
L6924D 11 Package mechanical data 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.
Package mechanical data Table 8. L6924D 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 30.
L6924D 12 Revision history Revision history Table 9. Document revision history Date Revision Changes 16-Dec-2005 1 First draft 20-Dec-2005 2 Package dimensions updated 10-Jan-2006 3 Few updates 14-Feb-2006 4 Part number updated 03-Jul-2006 5 Updates to equation in page 22, updated block diagram Figure 4.
L6924D Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale.
