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LTC4054ES5-4.2 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4054ES5-4.2 Datasheet(HTML) 9 Page - Linear Technology |
9 / 16 page 9 LTC4054-4.2/LTC4054X-4.2 405442xf than 2 µA and the supply current to less than 50µA. A new charge cycle can be initiated by reconnecting the program resistor. In manual shutdown, the CHRG pin is in a weak pull-down state as long as VCC is high enough to exceed the UVLO conditions. The CHRG pin is in a high impedance state if the LTC4054 is in undervoltage lockout mode: either VCC is within 100mV of the BAT pin voltage or insufficient voltage is applied to the VCC pin. Automatic Recharge Once the charge cycle is terminated, the LTC4054 continu- ously monitors the voltage on the BAT pin using a com- parator with a 2ms filter time (tRECHARGE). A charge cycle restarts when the battery voltage falls below 4.05V (which corresponds to approximately 80% to 90% battery capac- ity). This ensures that the battery is kept at or near a fully charged condition and eliminates the need for periodic charge cycle initiations. CHRG output enters a strong pull- down state during recharge cycles. OPERATIO lockout conditions. A weak pull-down indicates that VCC meets the UVLO conditions and the LTC4054 is ready to charge. High impedance indicates that the LTC4054 is in undervoltage lockout mode: either VCC is less than 100mV above the BAT pin voltage or insufficient voltage is applied to the VCC pin. A microprocessor can be used to distin- guish between these three states—this method is dis- cussed in the Applications Information section. Thermal Limiting An internal thermal feedback loop reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 120 °C. This feature protects the LTC4054 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 LTC4054. 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. ThinSOT power consid- erations are discussed further in the Applications Informa- tion section. 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. The UVLO circuit has a built-in hysteresis of 200mV. Furthermore, to protect against reverse current in the power MOSFET, the UVLO circuit keeps the charger in shutdown mode if VCC falls to within 30mV of the battery voltage. If the UVLO comparator is tripped, the charger will not come out of shutdown mode until VCC rises 100mV above the battery voltage. Manual Shutdown At any point in the charge cycle, the LTC4054 can be put into shutdown mode by removing RPROG thus floating the PROG pin. This reduces the battery drain current to less TRICKLE CHARGE MODE 1/10TH FULL CURRENT BAT > 2.9V BAT < 2.9V BAT > 2.9V CHRG: STRONG PULL-DOWN CHARGE MODE FULL CURRENT CHRG: STRONG PULL-DOWN SHUTDOWN MODE CHRG: Hi-Z IN UVLO WEAK PULL-DOWN OTHERWISE PROG RECONNECTED OR UVLO CONDITION STOPS PROG FLOATED OR UVLO CONDITION ICC DROPS TO <25µA POWER ON PROG < 100mV STANDBY MODE NO CHARGE CURRENT CHRG: WEAK PULL-DOWN 2.9V < BAT < 4.05V 405442 F01 Figure 1. State Diagram of a Typical Charge Cycle |
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Similar Description - LTC4054ES5-4.2 |
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