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LTC4001EUF-1-TRPBF Datasheet(PDF) 11 Page - Linear Technology |
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LTC4001EUF-1-TRPBF Datasheet(HTML) 11 Page - Linear Technology |
11 / 20 page LTC4001-1 11 40011fa APPLICATIONS INFORMATION The equations for calculating R1 (used in single resistor programming) differ from the equations for calculating RPROG and RIDET (2-resistor programming) and reflect the fact that the current from both the IDET and PROG pins must flow through a single resistor R1 when a single programming resistor is used. CHRG Status Output Pin When a charge cycle starts, the CHRG pin is pulled to ground by an internal N-channel MOSFET which is capable of driving an LED. When the charge current drops below the end-of-charge (IDET) threshold for at least 4ms, and the battery voltage is close to the float voltage, the N-channel MOSFET turns off and a weak 30μA current source to ground is connected to the CHRG pin. This weak pull-down remains until the charge cycle ends. After charging ends, the pin will become high impedance. By using two different value resistors, a microprocessor can detect three states from this pin (charging, end-of-charge and charging stopped). See Figure 2. To detect the charge mode, force the digital output pin, OUT, high and measure the voltage on the CHRG pin. The N-channel MOSFET will pull the pin low even with a 2k pull-up resistor. Once the charge current drops below the end-of-charge threshold, the N-channel MOSFET is turned off and a 30μA current source is connected to the CHRG pin. The IN pin will then be pulled high by the 2k resistor connected to OUT. Now force the OUT pin into a high impedance state, the current source will pull the pin low through the 390k resistor. When charging stops, the CHRG pin changes to a high impedance state and the 390k resistor will then pull the pin high to indicate charg- ing has stopped. Charge Termination Battery charging may be terminated several different ways, depending on the connections made to the TIMER pin. For time-based termination, connect a capacitor between the TIMER pin and GNDSENS (CTIMER= Time(Hrs) 0.0733μF). Charging may be terminated when charge current drops below the IDET threshold by tying TIMER to GNDSENS. Finally, charge termination may be defeated by tying TIMER to IDET. In this case, an external device can terminate charging by pulling the EN pin high. Battery Temperature Detection When battery temperature is out of range (either too hot or too cold) charging is temporarily halted and the FAULT pin is driven high. In addition, if the battery is still charg- ing at a high rate (greater than the IDET current) when a temperature fault occurs, the CHRG pin NMOS turns on and off at approximately 50kHz, alternating between a high and low duty factor at an approximate rate of 1.5Hz (Figure 3). This provides a low rate visual indication (1.5Hz) when driving an LED from the CHRG pin while providing a fast temperature fault indication (20μs typical) to a mi- croprocessor by tying the CHRG pin to an interrupt line. Serrations within this pulse are typically 500ns wide. Figure 2. Microprocessor Interface Figure 3. CHRG Temperature Fault Waveform LTC4001-1 VIN VDD IN OUT μPROCESSOR CHRG R2 2k R1 390k 40011 F02 20μs 40011 F03 667ms |
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