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LTM8062EVPBF Datasheet(PDF) 11 Page - Linear Technology |
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LTM8062EVPBF Datasheet(HTML) 11 Page - Linear Technology |
11 / 20 page LTM8062 11 8062f APPLICATIONS INFORMATION circuitry. For proper operation, it must be powered by at least 2.8V and no more than the absolute maximum rat- ing of 10V. In most applications, connect BIAS to BAT. If there is no BIAS supply available or the battery voltage is below 2.8V, the internal switch requires more headroom from VIN for proper operation. Please refer to the Typical Performance Characteristics curves for minimum start and running requirements under various battery conditions. When charging a 2-cell battery using a relatively high input voltage, the LTM8062 power dissipation can be reduced by connecting BIAS to a voltage between 2.8V and 3.3V. Output Capacitance In many applications, the internal BAT capacitance of the LTM8062 is sufficient for proper operation. There are cases, however, where it may be necessary to add capacitance or otherwise modify the output impedance of the LTM8062. Case 1: the μModule is physically located far from the battery and the added line impedance may interfere with the control loop. Case 2: the battery ESR is very small or very large; the LTM8062 controller is designed for a wide range, but some battery packs have an ESR outside of this range. Case 3: there is no battery at all. As the charger is designed to work with the ESR of the battery, the output may oscillate if no battery is present. The optimum ESR is about 100mΩ, but ESR values both higher and lower will work. Table 2 shows a sample of parts successfully tested by Linear Technology: Table 2 PART NUMBER DESCRIPTION MANUFACTURER 16TQC22M 22μF, 16V, POSCAP Sanyo 35SVPD18M 18μF, 35V, OS-CON Sanyo TPSD226M025R0100 22μF, 25V Tantalum AVX T495D226K025AS 22μF, 25V, Tantalum Kemet TPSC686M006R0150 68μF, 6V, Tantalum AVX TPSB476M006R0250 47μF, 6V, Tantalum AVX APXE100ARA680ME61G 68μF, 10V Aluminum Nippon Chemicon APS-150ELL680MHB5S 68μF, 25V Aluminum Nippon Chemicon If system constraints preclude the use of electrolytic ca- pacitors, a series R-C network may be used. Use a ceramic capacitor of at least 22μF and an equivalent resistance of 100mΩ. An example of this is shown in the Typical Ap- plications section. MPPT Temperature Compensation A typical solar panel is comprised of a number of series-con- nected cells, each cell being a forward-biased p-n junction. As such, the open-circuit voltage (VOC) of a solar cell has a temperature coefficient that is similar to a common p-n diode, or about –2mV/°C. The peak power point voltage (VMP) for a crystalline solar panel can be approximated as a fixed voltage below VOC, so the temperature coefficient for the peak power point is similar to that of VOC. Panel manufacturers typically specify the 25°C values for VOC, VMP, and the temperature coefficient for VOC, making determination of the temperature coefficient for VMP of a typical panel straight forward. The LTM8062 employs a feedback network to program the VIN input regulation voltage. Manipulation of the network makes for efficient implementation of various temperature compensation schemes for a maximum peak power tracking (MPPT) application. As the temperature characteristic for a typical solar panel VMP voltage is highly linear, a simple solution for tracking that characteristic can be implemented using a Linear Technology LM234 3-terminal temperature sensor. This creates an easily programmable, linear temperature dependent characteristic. In the circuit shown in Figure 4, RIN1 = –RSET •(TC • 4405), and RIN2 = RIN1 VMP(25°C)+RIN1 •(0.0674 / RSET) VINREG − 1 where TC = temperature coefficient (in V/°C), and VMP(25°C) = maximum power voltage at 25°C. Figure 4. MPPT Temperature Compensation Network VINREG 8062 F04 LTM8062 LINEAR TECHNOLOGY LM234 RIN1 RIN2 VIN VIN V+ V– R RSET |
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