ME4054 PDF

Thermal feedback regulates the charge current to limit the die temperature during high power operation or high ambient temperature. The charge voltage is fixed at 4. When the input supply wall adapter or USB supply is removed, the ME automatically enters a low current state, dropping the battery drain current to less than 2? The ME can be put into shutdown mode, reducing the supply current to 25? Other features include charge current monitor, undervoltage lockout, automatic recharge and a status pin to indicate charge termination and the presence of an input mA Single Cell Li-Ion Charger voltage.

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Thermal feedback regulates the charge current to limit the die temperature during high power operation or high ambient temperature. The charge voltage is fixed at 4. When the input supply wall adapter or USB supply is removed, the ME automatically enters a low current state, dropping the battery drain current to less than 2? The ME can be put into shutdown mode, reducing the supply current to 25? Other features include charge current monitor, undervoltage lockout, automatic recharge and a status pin to indicate charge termination and the presence of an input mA Single Cell Li-Ion Charger voltage.

VIN 4. A Supply Current in Shutdown 2. These values must therefore not be exceeded under any conditions. No blocking diode or external current sense resistor is required; thus, the basic charger circuit requires only two external components. If the BAT pin is less than 2. When the BAT pin voltage rises above 2.

When the BAT pin approaches the final float voltage 4. The battery charge current is times the current out of the PROG pin. This condition is detected by using an internal, filtered comparator to monitor the PROG pin. The 1ms filter time t TERM on the termination comparator ensures that transient loads of this nature do not result in premature charge cycle termination.

In this state, all loads on the BAT pin must be supplied by the battery. If this voltage drops below the 4. To manually restart a charge cycle when in standby mode, the input voltage must be removed and reapplied, or the charger must be shut down and restarted using the PROG pin. Figure 1 shows the state diagram of a typical charge cycle. V03 Page 7 of 16 ME 4. A and high impedance. The strong pull-down state indicates that the ME is in a charge cycle. Once the charge cycle has terminated, the pin state is determined by undervoltage lockout conditions.

A microprocessor can be used to distinguish between these three states—this method is discussed in the Applications Information section. This feature protects the ME from excessive temperature and allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the ME The charge current can be set according to typical not worst-case ambient temperature with the assurance that the charger will automatically reduce the current in worst-case conditions.

Undervoltage Lockout UVLO An internal undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until VCC rises above the undervoltage lockout threshold. This reduces the battery drain current to less than 2uA and the supply current to less than 50uA.

A new charge cycle can be initiated by reconnecting the program resistor. A charge cycle restarts when the battery voltage falls below 4.

This ensures that the battery is kept at or near a fully charged condition and eliminates the need for periodic charge cycle initiations. Stability Considerations The constant-voltage mode feedback loop is stable without an output capacitor provided a battery is connected to the charger output. With no battery present, an output capacitor is recommended to reduce ripple voltage as Fig. No series resistor is needed if tantalum capacitors are used. In constant-current mode, the PROG pin is in the feedback loop, not the battery.

The constant-current mode stability is affected by the impedance at the PROG pin. However, additional capacitance on this node reduces the maximum allowed program resistor. For example, if a switching power supply operating in low current mode is connected in parallel with the battery, the average current being pulled out of the BAT pin is typically of more interest than the instantaneous current pulses.

Power dissipation The conditions that cause the ME to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the IC.

The approximate ambient temperature at which the thermal feedback begins to protect the IC is: TA?? JA For example: The ME with 5V supply voltage through programmable provides full limiting current mA to a charge lithium-ion battery with 3. Thermal considerations Because of the small size of the thinSOT package, it is important to use a good thermal PC board layout to maximize the available charge current.

The thermal path for the heat generated by the IC is from the die to the copper lead frame, through the package leads, especially the ground lead to the PC board copper.

The PC board copper is the heat sink. The footprint copper pads should be as wide as possible and expand out to larger copper areas to spread and dissipate the heat to the surrounding ambient. Other heat sources on the board, not related to the charger, must also be considered when designing a PC board layout because they will affect overall temperature rise and the maximum charge current.

The following table lists thermal resistance for several different board sizes and copper areas. Increasing thermal regulation current It will effective to decrease the power dissipation through reduce the voltage of both ends of the inner MOSFET. In the thermal regulation, this action of transporting current to battery will raise.

One of the measure is through an external component as a resistor or diode to consume some power dissipation. For example: The ME with 5V supply voltage through programmable provides full limiting current mA to a charge lithium-ion battery with 3. While this application delivers more energy to the battery and reduces charge time in thermal mode, it may actually lengthen charge time in voltage mode if VCC becomes low enough to the ME into dropout.

This technique works best when R CC values are minimized to keep component size small and avoid dropout. Remember to choose a resistor with adequate power handling capability. VCC bypass capacitor Many types of capacitors can be used for input bypassing, however, caution must be exercised when using multilayer ceramic capacitors. Because of the self-resonant and high Q characteristics of some types of ceramic capacitors, high voltage transients can be generated under some start-up conditions, such as connecting the charger input to a live power source.

Adding a 1. Charging Current Soft Start ME includes a soft start circuit which used to maximize to reduce the surge current in the begging of charge cycle. This has the effect of minimizing the transient current load on the power supply during start-up. When a discharged battery is connected to the charger, the constant current portion of the charge cycle begins and the CHRG pin pulls to ground. When the battery is nearing full charge, the charger enters the constant-voltage portion of the charge cycle and the charge current begins to drop.

If the input voltage is removed or drops below the undervoltage lockout threshold, the CHRG pin becomes high impedance. To determine if there is a weak pull-down current, the OUT pin should be forced to a high impedance stage.

Reverse polarity input voltage protection In some applications, protection from reverse polarity voltage on VCC is desired. If the supply voltage is high enough, a series blocking diode can be used. V03 Page 13 of 16 ME Fig. Figure 8 shows an example of how to combine wall adapter and USB power inputs.

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Dull Can be hierarchical, e. Initials of the people on the team who will contribute to the task. MIT has a basic overview of project management that is available at this link. This way, one can get a quick reading of project progress by drawing a vertical line through the chart at the current date. These are risky because you may not have a good sense for how long the task will take.

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