L6924UTR STMICROELECTRONICS | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 37
Technical content
Datasheet sections
- 1 Description
- 2 Pin description
- 2.1 Pin description
- 3 Maximum ratings
- 4 Electrical characteristics
- 5 Block diagram
- 6 Operation description
- 6.1 Linear mode
- 6.2 Quasi-pulse mode
- 7 Applications information: charging process
- 7.1 Pre-charge phase
- 7.2 AC or USB mode
- 7.3 Fast charge phase
- 7.4 End-of-charge current
- 7.5 Recharge flow chart
- 7.6 Recharge threshold
- 7.7 Maximum charging time
- 8 Application information: m onitoring and protection
- 8.1 NTC thermistor
- 8.2 Battery absence detection
- 8.3 Status pins
- 8.4 Shutdown
- 9 Additional applications information
- 9.1 Selecting the input capacitor
- 9.2 Selecting the output capacitor
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 ■ 4.2 V output voltage with ± 1 % accuracy ■ Linear or quasi-pulse operating mode ■ Closed loop thermal control ■ Programmable end-of-charge current ■ Programmable charge timer ■ (NTC) or (PTC) thermistor interface for battery temperature monitoring and protection ■ Status outputs to drive LEDs or to interface with a host processor ■ Small VFQFPN 16-leads package (3 x 3 mm)
Applications
■ PDAs, GPS and MP3 players ■ USB powered devices ■ Cellular phones ■ Digital still cameras ■ Standalone chargers ■ Wireless appliances VFQFPN16 Table 1. Device summary
1 Description
device can operate in quasi-pulse mode, dramatically reducing the power dissipation. Figure 2. Basic application schematic Figure 1. Minimum size application board
2 Pin description
Figure 3. Pin connection (top view)
2.1 Pin description
Table 2. Pin functions 1I V IN Input pin of the power stage. Supply voltage pin of the signal circuitry. 3 - 4 O ST 2-ST1 Open-collector status pins. Maximum charging time program pin. temperature window see Chapter 8.1: NTC thermistor on page 23.
9 I ISEL
connected to ground or left floating.
10 I V
It senses the battery voltage to control the voltage regulation loop.
13 I/O I END
current delivered to the battery (gas gauge function).
14 I MODE
pin status does not affect the current set.
15 I I USB
mode is selected with the ISEL pin.
16 I I AC
Table 2. Pin functions (continued)
3 Maximum ratings
program and other relevant quality documents. Table 3. Absolute maximum ratings Table 4. Thermal data
- Device mounted on demonstration board
4 Electrical characteristics
TJ = 25 °C, VIN = 5 V, unless otherwise specified. Table 5. Electrical characteristics
- Device working in quasi pulse mode
Table 5. Electrical characteristics (continued)
5 Block diagram
Figure 4. Block diagram
L6924U Operation description Doc ID 14716 Rev 2 11/37
6 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 2.5 V) the L6924U can also work as a quasi-pulse charger when powered from a current limited adapter. To work in this condition, it is enough to set the device’s charging current higher than the adapter’s one (Chapter 6.2: Quasi-pulse mode on page 14). The advantage of the linear charging approach is that the device has a direct control of the charging current and so the designer needn’t to rely on power source. However, the advantage of the quasi-pulse approach is that the power dissipated inside the portable equipment is dramatically reduced. The L6924U charges the battery in three phases:
- Pre-charge constant current: in this phase (active when the battery is deeply discharged) the battery is charged with a low current (internally set to 10 % of the fast- charge current).
- Fast-charge constant current: in this phase the device charges the battery with the maximum current (I AC for AC adapter mode, IUSB for USB mode).
- Constant voltage: when the battery voltage reaches the selected output voltage, the device starts to reduce the current, until the charge termination is done. The full flexibility is provided by:
- Programmable fast-charging current (IAC or IUSB) (Chapter 7.3 on page 18).
- Programmable end of charge current threshold (IENDTH) (Chapter 7.4 on page 20).
- Programmable end of charge timer (TMAXCH) (Chapter 7.7 on page 21). If a PTC or NTC resistor is used, the device can monitor the battery temperature in order to protect the battery from operating under unsafe thermal conditions. Beside the good thermal behavior guaranteed by low thermal resistance of the package, additional safety is provided by the built-in temperature control loop. The IC monitors continuously its junction temperature. When the temperature reaches approximately 120 °C, the thermal control loop starts working, and reduces the charging current, in order to keep the IC junction temperature at 120 °C. Two open collector outputs are available for diagnostic purpose (status pins ST1 and ST2). They can be also used to drive external LEDs or to interface with a microcontroller. The voltage across the resistor connected between I END and GND gives information about the actual charging current (working as a gas gauge), and it can be easily fed into a microcontroller ADC. Battery disconnection control is provided thanks to the differentiated sensing and forcing output pins. A small current is sunk and forced through V OUT. If VOSNS doesn’t detect the battery, the IC goes into a standby mode. Figure 5 on page 12 shows the real charging profile of a Li-Ion battery, with a fast charge current of 450 mA (R1 or R2 = 26 kΩ).
Figure 5. Li-Ion charging profile
6.1 Linear mode
constant current limit protection.
- Pre-charging current ("pre-charge" phase).
- Constant current ("fast-charge" phase).
- Constant voltage ("voltage regulation" phase). VADP is the output voltage of the upstream AC-DC adapter that is, in turn, the input voltage of the L6924U. If the battery voltage is lower than the default pre-charge voltage (VPRETH), the pre-charge phase takes place. The battery is pre-charged with a low current, internally set to 10 % of the fast charge current. When the battery voltage goes higher than V PRETH, the battery is charged with the fast charge current (IUSB or IAC according to the selection of the MODE pin). Finally, when the battery voltage is close to the regulated output voltage (4.2 V), the voltage regulation phase takes place and the charging current is reduced. The charging process ends when the charging current reaches the programmed value (I ENDTH) or when the charging timer expires. Figure 6 shows the different phases. 0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.450 0.500 0 200 400 600 800 1000 1200 Charging time (sec) Ichg (A) 0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 Vbatt (V) Ichg Vbatt
Figure 6. Typical charge curves in linear mode dissipated depends on the thermal impedance of the device mounted on board.
6.2 Quasi-pulse mode
Figure 7. Typical charge curves in quasi pulse mode
Operation description L6924U 16/37 Doc ID 14716 Rev 2 Equation 5 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. LIMBATADPDIS I)VV(P ×−=
7 Applications information: charging process
Figure 9. Charging process flow chart
7.1 Pre-charge phase
(VPRETH), internally set to 3 V. time, a fault is given (Chapter 7.7: Maximum charging time on page 21). pre-charge phase is skipped.
7.2 AC or USB mode
The L6924U can charge batteries from both an AC adapter and USB inputs. The power supply type can be chosen by driving the MODE pin. charge phase), regardless of the resistor connected to IAC. Figure 10. MODE pin selection
7.3 Fast charge phase
enters the fast-charge phase. mode) with an accuracy of 7 %.
7.4 End-of-charge current
Figure 13. I END pin connection Where KEND is 1050 and VMIN is 50 mV. end of charge and the charge process ends. microcontroller to check the charge status like a gas gauge.
7.5 Recharge flow chart
Figure 14. Recharge flow chart
7.6 Recharge threshold
7.7 Maximum charging time
Note: The maximum recommended C TPRG value must be less than 50 nF .
Figure 15. T PRG pin connection TMAXCH is the charging time given in seconds. generated, and the charge process finishes.
8 Application information: monitoring and protection
feature prevents the L6924U from having thermal issues typically present in a linear charger.
8.1 NTC thermistor
indicates a fault condition through the status pin. Figure 16. Power dissipation in both lin ear and quasi pulse modes with thermal loop
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. The correct resistance ratio to set the low temperature limit at 0 °C can be found with the following equation: Equation 12 Where RUP is the pull-up resistor, VREF is equal to 1.8 V, and RNTC0°C is the value of the NTC at 0 °C. Since at the low temperature limit VMINTH = 900 mV: Equation 13 It follows that: Equation 14 Similarly, when the battery is at the high temperature limit, the TH pin voltage is 225 mV. The correct resistance ratio to set the high temperature limit at 50 °C can be found with the following equation: Equation 15 Where RNTC50°C is the value of the NTC at 50 °C. Considering VMAXTH = 225 mV it follows that: Equation 16 Consequently: Equation 17 CNTCUP CNTC REFMINTH RR RVV +×= CNTCUP CNTC RR R +×= 08.19.0 UPCNTC RR =°0 CNTCUP CNTC REFMAXTH RR RVV +×= CNTCUP CNTC RR R +×= 508.1225.0 UP CNTC RR =°
Application information: monitoring and protection L6924U 26/37 Doc ID 14716 Rev 2 Based on Equation 14 and Equation 17, it derives that: Equation 18 The temperature hysteresis can be estimated by the equation: Equation 19 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. For NTCT values, see the characteristics of the NTC manufacturers (e.g. the 2322615 series by VISHAY). At low temperature, the hysteresis is approximately: Equation 20 Obviously at high temperature hysteresis is: Equation 21 Considering typical values for NTC0°C and NTC50°C, the hysteresis is: Equation 22 And: Equation 23 If a PTC connected to GND is used, the selection is the same as above, the only difference is when the battery temperature increases, the voltage on the TH pin increases, and vice versa. For applications that do not need a monitor of the battery temperature, the NTC can be replaced with a simple resistor whose value is one half of the pull-up resistor R UP. In this case, the voltage at the TH pin is always inside the voltage window, and the charge is always enabled. 0 = CNTC CNTC R R TTH HYSTHTH HYS NTCV VVT × CNTCmV mVmVT CHYS −=° 0900 780900 CNTCmV mVmVT CHYS −=° 50225 248225 CmV mVmVT CHYS o5.2051.0900 780900 0 ≅× −=° CmV mVmVT CHYS o5.2039.0225 248225 50 −≅× −=°
8.2 Battery absence detection
insertion of the battery. If the battery is removed, the charge current falls below the IENDTH.
8.3 Status pins
external power source, by a resistor, or to communicate to a host processor. Figure 20. Battery absence detection flow chart
8.4 Shutdown
The L6924U has a shutdown pin; when the pin is connected to GND, the device is operating. Figure 21. ST1 and ST2 connection with LEDs or microcontroller Table 6. Status LEDs Indications
L6924U Additional applications information Doc ID 14716 Rev 2 29/37
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. This ensures proper operation of battery absent detection in removable battery pack applications.
9.3 Layout guidelines and demonstration board
The thermal loop keeps the device at a constant temperature of approximately 120 °C which in turn, reduces ICHG. However, in order to maximize the current capability, it is important to ensure a good thermal path. Therefore, the exposed pad must be properly soldered to the board and connected to the other layer through thermal vias. The recommended copper thickness of the layers is 70 μm or more. The exposed pad must be electrically connected to GND. Figure 22 shows the thermal image of the board with the power dissipation of 1 W. In this instance, the temperature of the case is 89 °C, but the junction temperature of the device is given by the following equation: Equation 25 Where the RthJA of the device mounted on board is 75 °C/W, the power dissipated is 1 W, and the ambient temperature is 25 °C. In this case the junction temperature is: Equation 26 AMBDISSATHJJ TPRT +×= − CTJ o10025175 =+×=
Figure 25. Demonstration board schematic Table 7. Demonstration board components description R1 24 k Ω AC mode fast-charge current resistor. Used to set the charging current in AC mode. gauge” when measuring the voltage across on it. R4 1 k Ω Pull up resistor. Connected between VREF and TH pin. R6 1 k Ω Pull up resistor. To be used when the ST2 is connected to a LED. MAX capacitor. Used to set the maximum charging time. C4 1 nF V REF filter capacitor. J1 ST2 jumper. Using to select the LED or the external microcontroller. J2 ST1 jumper. Using to select the LED or the external microcontroller. J4 Low power/ high power USB mode selection jumper. J5 AC/USB mode selection jumper.
Application idea: dual input management with AC priority L6924U 32/37 Doc ID 14716 Rev 2 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. If only the AC adapter is available, since the gates of Q1 and Q2 are connected to AC, both MOSFETs are off. The AC adapter voltage is provided to the V IN pin through the diode D1. The voltage at the VIN pin is: A correct choice of this diode is important to limit Vdiode and keeping VIN as close as possible to AC. In this condition the MODE pin is low. This sets the L6924U in AC mode and the battery is charged with the current programmed by RAC. When only the USB power source is available, both Q1 and Q2 switch on and the pin VIN is connected to USB. The MODE pin is connected to the drains of Q1 and Q2 and is high. Therefore the USB mode for the L6924U is selected and the battery is charged with a current in accordance with the resistor connected to the pin I USB (RUSB). The voltage of the VIN pin is given by: The voltage drop across the MOSFETs must be kept as low as possible to avoid reducing too much the voltage of the VIN pin. When both sources are present, this circuit gives the priority to the AC adapter. In fact, for VAC ≥ 5 V, surely both Q1 and Q2 are off and VIN is connected to the AC adapter through D1. The MODE pin is kept low and L6924U is set to AC mode. The use of two P-channel MOSFETs connected as shown in Figure 26 is particularly useful in this case because they remove any path between the two power sources. diodeACIN VVV −= ( ) USB2Q_DSon1Q_DSonUSBIN IRRVV ⋅+−=
Figure 26. Dual input management
Package mechanical data L6924U 34/37 Doc ID 14716 Rev 2 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.
Table 8. VFQFPN16 (3 x 3 mm.) mechanical data Figure 27. Package dimensions
Table 9. Document revision history 22-Sep-2010 2 Modified: Table 8 and Figure 27 on page 35. Minor changes.