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LTC4001 Datasheet(PDF) 10 Page - Linear Technology |
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LTC4001 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 20 page  10 LTC4001 4001f APPLICATIO S I FOR ATIO Soft-Start and Compensation Capacitor Selection The LTC4001 has a low current trickle charger and a PWM-based high current charger. Soft-start is used when- ever the high rate charger is initially turned on, preventing high start-up current. Soft-start ramp rate is set by the internal 12.8 µA pull-up current and an external capacitor. The control range on the SS pin is approximately 0.3V to 1.6V. With a 0.1 µF capacitor, the time to ramp up to maximum duty cycle is approximately 10ms. The external capacitor on the SS pin also sets the compen- sation for the current control loop and the float voltage control loop. A minimum capacitance of 10nF is required. Charge Current and IDET Programming The LTC4001 has two different charge modes. If the battery is severely depleted (battery voltage less than 2.9V) a 50mA trickle current is initially used. If the battery voltage is greater than the trickle charge threshold, high rate charging is used. This higher charge current is programmable and is ap- proximately 915 times the current delivered by the PROG pin. This current is usually set with an external resistor from PROG to GNDSENS, but it may also be set with a current output DAC connected to the PROG pin. The voltage on the PROG pin is nominally 1.213V. For 2A charge current: R V A PROG = ≅Ω 915 1 213 2 554 9 •. . The IDET threshold (a charge current threshold used to determine when the battery is nearly fully charged) is programmed in much the same way as the PROG pin, except that the IDET threshold is 91.5 times the current delivered by the IDET pin. This current is usually set with an external resistor from IDET to ground, but it may also be set with a current output DAC. The voltage on the PROG pin is nominally 1.213V. For 200mA IDET current (corresponding to C/10 for a 2AHr battery): R V A IDET = ≅Ω 91 5 1 213 02 554 9 .• . . . 1.10k Ω programs approximately 100mA and 274Ω ap- proximately 400mA. For applications where IDET is set to one tenth of the high rate charge current, and slightly poorer charger current and IDET threshold accuracy is acceptable, the PROG and IDET pins may be tied together and a single resistor, R1, can program both (Figure 1). R ICHARGE 1 457 5 1 213 = .• . and IDET ICHARGE = 10 Figure 1. Programming Charge Current and IDET Threshold with a Single Resistor PROG LTC4001 IDET R1 274 Ω FOR 2A GNDSENS 4001 F01 |
Similar Part No. - LTC4001_15 |
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Similar Description - LTC4001_15 |
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