Pre -charging voltage

If the VPRE pin is floating, the default value of VPRETH is set, which is equal to 2.8V (VPRETHDEFAULT). Otherwise, the device can program the value between the value between the VPRE pin and GND by connecting the resistor, Figure 12. In this case, RVPRE is given by Formula:

Among them, RVPRE is the resistance between VPRE and GND, and RPRG is used to set up charging current (see Section 7.4 Section 7.4 : Quick charging current), VPRETH is the selected threshold. Safety timer also exists. If the battery voltage does not exceed VPRETH, it expires before this time (see Section 7.8: the maximum charging time). If the battery voltage is higher than the VPRETH during the charging process, the pre -charging phase is skipping.

Quick charging current

When the battery voltage reaches the pre -charging voltage threshold (VPRETH), the L6924D starts the fast charging phase. At this stage, the device uses a constant current, ICHG, which can be programmed by an external resistor. The accuracy of the resistor is 13%. The formulas used to choose RPRG are as follows:

Among them, KPRG is a constant, equal to 9500. At this stage, the battery voltage rose until it reached the programming output voltage. Safety timer also exists. If this time expires, the failure (Section 7.8: Maximum charging time)

The ending current of charging

When the charging voltage is close to the selection value (4.1V or 4.2V), the charging voltage is close to the selection value (4.1V or 4.2V). The voltage adjustment phase occurred. The charging current began to decrease until it was lower than the A programming end value. INDTH depended on the connection to the IEND pin and GND Figure 14. The formula describing this relationship is as follows:

Among them, Kend is 1050; Vmin is 50MV.

Generally, this current level is used to terminate the charging process. However, this is also possible to disable the termination of charging (Chapter 7.9) according to the current level. This pin can also be used to monitor charging current because the current injected in the REND is proportional to ICHG. The microcontroller can use a voltage across REND to check the charging state like an gas meter.

Charging threshold

When the charging is over, the battery voltage is lower than the charging voltage threshold (VRCH), and the device returns the charging state. The value of the charging threshold is 150 millivoli.

Maximum charging time

In order to avoid charging a long -term battery for a long time, L6924D may set the maximum charging time from the fast charging stage.This timer can set a capacitor and connect between the TPRG pin and GND. CTPRG is an external capacitor (unit: NF). The following formulas are concluded:

Note: ]

VREF u003d 1.8 il,

kt u003d 279 x 105, vbg u003d 1.23V, and

tmaxh is the charging time in seconds in seconds.

If the battery does not reach the end of the charging before the time expires, the fault is released. In addition, in the pre -charging stage, there is also a safety timer, which is given from the following formulas:

Discard the fault signal, the charging process is terminated.

As shown in FIG. 17, the charging end current of connecting A can be set at the resistance between the INDTHIEND pin and GND. When the charging current drops to this value, then go to the fault time, and the state pins notify the charging process. This time the failure time is expressed as:

However, the termination of the charger process depends on the state of the VPRE pin: if the voltage at the VPRE pins is higher than 0.8V, the voltage of the VPRE pins is higher than 0.8V, and The charging process is actually terminated when the charging current reaches the INDTH. If the voltage of the VPRE pin is lower than 0.8V, the charging process will not be terminated, and the charging current can be lower than INDTH. The state pins notify the charging end as a state of failure, but the equipment continues to charge. The charging process ends when the Tmaxh ends and the fault conditions are issued. In the pre -charging phase, if the voltage on the VPRE pins is lower than 0.8V, the device will automatically set VPRETHDEFAULT. If the voltage on the VPRE pins is lower than 0.5V (edge u200bu200bsensitive), the timer will be reset, both are in the pre -charging and fast charging phase.

Application information: Monitoring and protecting L6924D uses VFQFPN 3 mm x 3 mm 16 -cut packaging, with an exposed pad, allowing users to have a compact application and good thermal performance at the same time. L6924D due to the exposed pad (about 75 ° C/W, depending on the characteristics on the board). In addition, the built -in thermal protection function can prevent L6924D because linear chargers usually have heat problems. Thermal control is achieved through a heat circuit, which can reduce the charging current when the knot temperature reaches about 120 ° C. This avoids further temperature rise and keeps warm. This simplifies the design of thermal application and protection equipment from ultra -temperature damage. The above figure shows how the thermal circuit acts (using the dotted line), when the temperature reaches 120 ° C.

FIG. 18. Linear and quasi -pulse mode power consumption with hot circuit

The negative temperature coefficient thermistor

This device allows designers to monitor the battery temperature by measuring voltage to monitor the battery temperature Through NTC or PTC resistor. The working temperature range of lithium -ion batteries is very narrow, usually between 0 ° C and 50 ° C. This window can be composed of a NTC thermistor that connects to GND through an external frequency device and a resistor connected to a VREF. The voltage on TH pins exceeds the minimum or maximum voltage threshold (internal window comparator). When the voltage (and temperature) returns to the window range, the device restarts the charging process. In addition, there is a lag in the upper and lower thresholds, as shown in Figure 20

Note: When the battery temperature is between 0 ° C and 50 ° C, TBAT u003d normal

When the TH pin voltage rises and exceeds 50%of the VMinth u003d VREF (900mv typical value), L6924D stops charging and indicates the fault through the status pin. The equipment is restarted when the voltage of the tH needle is lower than the vminth_hys u003d 780mv (typical value), and the battery is charged. When the TH pin voltage is lower than the Vmaxth, what is related to the high temperature limit of VREF (225mv typical values), L6924D stops charging until Vmax_hys u003d 248mv (typical values). When the battery is at a low temperature limit, the fourth pins voltage is 900 millivolves. The resistance ratio of the low temperature limit to 0 ° C correctly can be found in the following formulas:

Among them, RUP is a pull -up resistor, VREF is equal to 1.8V, RNTC0 ° C. The value of NTC is 0 ° C. Due to the low temperature limit VMINTH u003d 900mv:

The battery lack of electricity detection

This function provides a battery deficiency detection scheme to detect remove or insert the battery. If the battery is removed, the charging current will be lower than INDTH. At the end of the fault time, detect the current IdETECT, which is equal to 1MA, sinking from the output place for a period of time T detection. This device checks the voltage of the output end. If it is lower than VPRETH, the current is equal to the TOIDETECT into the output capacitor for T testing and check the output voltage higher than VOPRGTH-50MV. If the battery changes from VPRETH to VABS during the detection time, vice versa, which means that the battery is connected to the charger. T test value is expressed as:

Status pin

In order to indicate the status of various chargers, there are two epigrons output pins, ST1 and 2. These states pins can be used to drive the state of the state indicator light to drive and the external connection, and communicate with the host processor through the resistance. These needles cannot be connected to VIN when it overcome the absolute value (6V).

Close

L6924D has a shutdown pin; when the pin is connected to the GND, the device is running. When the pin is kept floating, the device enters the shutdown mode and decreases significantly from the input to 60 μA (typical value). In this case, VREF is closed.

Other application information

Select the input capacitor

In most applications, 1 μF ceramic capacitors placed near VIN and VINSN pins can be used to filter high -frequency remove noise.

Selecting output capacitors

Generally, 1 μF ceramic capacitors placed near Vout and VOUTSN pins are sufficient to keep the voltage control loop stable. This ensures that the lack of battery detection is applied in the dismantling battery pack.

Layout Guide and Demonstration Board Description

The thermal circuit keeps the device at a constant temperature of about 120 ° C. This turns reduces ICHG. However, in order to maximize the current ability, it is important to ensure a good heat path. Therefore, exposed pads must be welded correctly to connect to another layer through the air -pass hole. The thickness of the recommended copper layer is 70 μm or higher. Bare pads must be connected to GND. Figure 24 shows a circuit board with a power consumption of 1W. In this case, the temperature of the shell is 89 ° C, but the knot temperature of the device is given by the following formula: when the RTH J-A installed on the ship is 75 ° C/W, the power consumption is 1W, and the environment is the environment. The temperature is 25 ° C. In this case, the knot temperature is: tj u003d rthj u0026#8722; A × PDISS+TAMB formula TJ CO u003d 75 × 1+25 u003d 100 Powers