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LTC4063 Datasheet(PDF) 11 Page - Linear Integrated Systems |
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LTC4063 Datasheet(HTML) 11 Page - Linear Integrated Systems |
11 / 18 page LTC4065L/ LTC4065LX/LTC4065L-4.1 11 4065lfb OPERATION Charge Current Soft-Start and Soft-Stop The LTC4065L includes a soft-start circuit to minimize the inrush current at the start of a charge cycle. When a charge cycle is initiated, the charge current ramps from zero to the full-scale current over a period of approximately 170μs. Likewise, internal circuitry slowly ramps the charge current from full-scale to zero when the charger is shut off or self terminates. This has the effect of minimizing the transient current load on the power supply during start-up and charge termination. Constant-Current/Constant-Voltage/ Constant-Temperature The LTC4065L use a unique architecture to charge a bat- tery in a constant-current, constant-voltage and constant- temperature fashion. Figure 1 shows a simplified block diagram of the LTC4065L. Three of the amplifier feedback loops shown control the constant-current, CA, constant- voltage, VA, and constant-temperature, TA modes. A fourth amplifier feedback loop, MA, is used to increase the output impedance of the current source pair; M1 and M2 (note that M1 is the internal P-channel power MOSFET). It ensures that the drain current of M1 is exactly 205 times greater than the drain current of M2. Amplifiers CA and VA are used in separate feedback loops to force the charger into constant-current or constant- voltage mode, respectively. Diodes D1 and D2 provide priority to either the constant-current or constant-voltage loop, whichever is trying to reduce the charge current the most. The output of the other amplifier saturates low which effectively removes its loop from the system. When in constant-current mode, CA servos the voltage at the PROG pin to be precisely 1V. VA servos its inverting input to an internal reference voltage when in constant-voltage mode and the internal resistor divider, made up of R1 and R2, ensures that the battery voltage is maintained at 4.2V for LTC4065L/LTC4065LX or 4.1V for LTC4065L-4.1. The PROG pin voltage gives an indication of the charge current during constant-voltage mode as discussed in “Program- ming Charge Current”. The transconductance amplifier, TA, limits the die tempera- ture to approximately 115°C when in constant-temperature mode. Diode D3 ensures that TA does not affect the charge current when the die temperature is below approximately 115°C. The PROG pin voltage continues to give an indica- tion of the charge current. In typical operation, the charge cycle begins in constant- current mode with the current delivered to the battery equal to 205V/RPROG. If the power dissipation of the LTC4065L results in the junction temperature approaching 115°C, the amplifier (TA) will begin decreasing the charge current to limit the die temperature to approximately 115°C. As the battery voltage rises, the LTC4065L either returns to constant-current mode or enters constant-voltage mode straight from constant-temperature mode. Regardless of mode, the voltage at the PROG pin is proportional to the current delivered to the battery. |
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