New independent linear lithium ion battery charger
rechargeable batteries are often used to power portable devices such as digital cameras, PDAs, mobile and MP3 players. AC adapter is the most commonly used charging power supply. However, more and more applications are connecting to the available USB power supply. Ltc4061 and ltc4062 are designed to charge a single lithium-ion battery using either of the above two power supplies
both devices use a constant current/constant voltage algorithm to provide a charging current of up to 1a (settable), with a final floating voltage accuracy of ± 0.35%. They include an internal p-channel power MOSFET and thermal adjustment circuit, without the use of isolated diodes to provide an overall solution tube or external detection resistors; Therefore, the basic charger circuit requires only two external components
ltc4061 and ltc4062 include a charge termination circuit based on settable time and settable current. The open drain status pin CHRG (can be set according to the needs of the application to indicate the charging status of the battery. The ltc4061 provides an AC power supply open drain status pin ACPR () to indicate that sufficient voltage is available at the input to charge a battery. Other safety features designed to maximize battery life and improve reliability include negative temperature coefficient (NTC) battery temperature detection (ltc4061) and smartstarttm charging algorithm, which can prolong the battery life by preventing unnecessary charging cycles
in the ltc4062, a low IQ Precision Comparator replaces the NTC and ACPR (functions) on the ltc4061. When no input power is applied, the ltc4062 internal low power comparator can work normally and only absorb 10% from the battery μ A current. With input power applied, ltc4061 and ltc4062 can be placed in shutdown mode to reduce the supply current to a very low value (20 μ A) And reduce the battery leakage current to 2 μ Below a
the internal thermal feedback function is responsible for regulating the charging current to limit the chip temperature under high-power operation or high ambient temperature conditions
ltc4061 and ltc4062 provide a lot of design flexibility, including settable charging current and settable total time termination or settable current termination. The maximum charging current is set by a resistor connected between the prog pin and ground. The output charging current of bat pin can be determined at any time by monitoring the voltage of prog pin. The formula adopted is as follows:
ibat = (vprog/rprog) · 1000
current detection threshold idect is set by connecting a resistor rdetect between IDET and ground. This threshold is used to change CHRG (the state of the timer pin to indicate that the battery is nearly fully charged. Alternatively, the threshold can also be used as the termination current threshold for ending the charging cycle.
when the total time termination is adopted, charging huge plastic waste has become an urgent problem to be solved. The power time is set by connecting a capacitor ctimer between timer and ground.
timer pin is responsible for controlling the termination method of ltc4061 and ltc4062. Connect an external The capacitor to timer pin will start an internal timer, which will stop the charger operation after the set time period. Grounding the timer pin and connecting a resistor to the IDET pin will cause the charging cycle to terminate immediately after the charging current drops below a set threshold (idetec). Connecting the timer pin to the input power supply will disable the internal termination function, so that the charger can be manually turned off by enabling the (en() input
c/5 (PIN) on ltc4061 and ltc4062 provides an easy way to select between two different power modes, i.e. high power and low power. When c/5 (pin is logic high), the charging current is set to 100% of the current set by the prog pin resistor (up to 1a). When the c/5 (pin is at the logic low level), the current limit is set to 20% of the current set by the prog pin resistor. A weak pull-down resistor is deployed on the c/5 (pin to preset it to the low power state.
Figure 1: ltc4061 and ltc4062 usb/
AC adapter power supply lithium ion battery charger configuration
as shown in Figure 1, c/5 (the pin provides great flexibility in application and can automatically select between AC adapter and USB power supply. If AC adapter is connected and its voltage is higher than the Vth of MP1, the power supply is applied through diode D1. Moreover, since MP1 is in an open circuit state, the power supply available through USB port is not used. Mn1 is closed and 3.3k Ω and 2K Ω resistors are connected in parallel, so the total maximum charging current is set as high as 8 00Ma (160mA if c/5 (pin is set to low level). If the AC adapter is not connected, USB is responsible for supplying power to the charger; When Mn1 is open circuit, only 2K Ω resistor is left to set the charging current as high as 500mA (maximum). Using c/5 (pin, the charging current can be set to 100mA or 500mA according to the needs of USB applications.
Figure 2: ltc4062 lithium ion battery charger configuration with time termination and battery detection
eliminates unnecessary charging cycles
ltc4061 and ltc4062 are designed to avoid unnecessary charging cycles and to extend the service life of lithium ion batteries. When the device is initially powered on or out of shutdown mode, ltc4061 And ltc4062 will check the voltage on the bat pin to determine its initial state. If the bat pin voltage is lower than the recharge threshold of 4.1V (corresponding to about 80%_90% of the battery capacity), ltc4061 and ltc4062 will enter the charging mode and start a complete charging cycle. If the bat pin voltage is higher than 4.1V, the battery is close to the full charge state, and the charger will not start a charging cycle, but enter the standby mode. In standby mode, the charger continuously monitors the bat pin voltage. When the bat pin voltage drops below 4.1V, the charging cycle will restart automatically, and the internal timer will be reset to 50% of the set charging time (if the time termination method is used). These functions eliminate the need for periodic charging cycle startup, ensure that the battery is always in a fully charged state, and reduce the number of unnecessary charging cycles, thus extending the service life of the battery
fault detection and reporting
as shown in Figure 3, ltc4061 has an NTC (negative temperature coefficient) input to determine whether the charging operation is normal or not according to the temperature of the battery. If the battery temperature is higher or lower than the safe level, the charging will be suspended, the internal timer will be frozen, and a square wave will be used to drive the CHRG (pin output) to flash at the frequency set by ctimer (if timer mode is adopted) or 1.5Hz (when current or user termination mode is adopted) (timer pin is connected to GND or input power supply). The flicker frequency when using ctimer is set by the following formula:
fchrg (= 0.1 μ F/ctimer · 1.5hz
grounding the NTC pin can disable this function
although only ltc4061 has the ability to notify temperature faults, both devices can notify the failure of the battery. When the bat pin voltage is lower than the trickle charging threshold (vtrikl) of 2.9v, the charging current will be reduced to 10% of the set value. If the battery is in trickle charging mode for more than 25% of the set total charging time, the charger will stop charging and report battery damage. Ltc4061 and ltc4062 report the fault status by using a square wave to drive the CHRG (output). The duty cycle of the oscillation is 50% and the frequency is set by ctimer.
an LED driven by the CHRG (output) shows a pulse flashing pattern to inform the user that the battery needs to be replaced. The generated small excitation is amplified and applied to the test piece for material fatigue test. If it is necessary to clear the battery failure fault, you can use en (input conversion or remove the power supply of the VCC and reapply it. The battery failure detection function is only available when the time termination method is used.
Figure 3: the functional difference between ltc4061 and ltc4062
except for the NTC function, Ltc4061 also has an ACPR (power status indicator). When the VCC pin has enough voltage to charge a battery, an open drain NMOS device will be used to pull the pin to the low level. Otherwise, the pin will be in a high impedance state.
ltc4062 uses a non dedicated accurate, low power comparator to replace the NTC and ACPR of ltc4061 (function. The comparator is powered by bat pin, and the current consumption is only 10 μ A。 But in practice, the open drain output (out) can drive an LED. Possible uses of the comparator include accurate low battery power detection (as shown in Figure 2) and user settable input power monitoring
ltc4061 and ltc4062 are complete linear lithium ion battery chargers for AC adapter and USB power supply. They extend battery life by eliminating unnecessary charging cycles. Ltc4061 and ltc4062 are ideal for many portable USB applications due to their versatility in charge termination, low quiescent current, simplicity, high integration and small overall dimensions. Ltc4061 and ltc4062 are available in small form factor 10 pin flat 3mm x 3mm DFN packages. (end)
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