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LM3595 数据表(PDF) 9 Page - National Semiconductor (TI) |
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LM3595 数据表(HTML) 9 Page - National Semiconductor (TI) |
9 / 11 page Application Information (Continued) TABLE 2. LED Current when using the BRGT input with BR-ON = V IN R SET ( Ω) 4.99k Ω 6.25k Ω 8.25k Ω 12.4k Ω VBRGT(V) I LED(mA) I LED(mA) I LED(mA) I LED(mA) 0.0 0.1 0.1 0.1 0.1 0.5 4.1 3.3 2.5 1.6 1.0 8.1 6.7 4.9 3.3 1.5 12.2 10.0 7.4 4.9 2.0 16.3 13.3 9.9 6.6 2.5 20.4 16.7 12.3 8.2 3.0 24.5 20.0 14.8 9.8 LED SELECTION The LM3595 is designed to drive white-LEDs with a typical forward voltage of 3.0V to 4.0V. The maximum LED forward voltage that the LM3595 can accommodate is highly depen- dant upon V IN and IOUTX. (See the section on Output Current Capability for more information on finding maximum V OUTX.) For applications that demand color and brightness matching, care must be taken to select LEDs from the same chroma- ticity group. Forward current matching is assured over the LED process variations due to the constant current outputs of the LM3595. TABLE 3. White LED Selection: Component Manufacture Contact Manufacturer Contact Osram www.osram-os.com Nichia www.nichia.com PARALLEL OUTx OUTPUTS FOR INCREASED CURRENT DRIVE Outputs OUT1 through OUT4 may be connected together in any combination to drive higher currents through fewer LEDs. For example in Figure 1, outputs OUT1 and OUT2 are connected together to drive one LED while OUT3 and OUT4 are connected together to drive a second LED. With this configuration, two parallel current sources of equal value provide current to each LED. R SET and VBRGT should therefore be chosen so that the current through each output is programmed to 50% of the desired current through the parallel connected LEDs. For example, if 30mA is the de- sired drive current for 2 parallel connected LEDs, R SET and V BRGTshould be selected so that the current through each of the outputs is 15mA. Other combinations of parallel outputs may be implemented in similar fashions, such as in Figure 2. Connecting outputs in parallel does not affect internal opera- tion of the LM3595 and has no impact on the Electrical Characteristics and limits previously presented. The avail- able diode output current, maximum diode voltage, and all other specifications provided in the Electrical Characteristics table apply to parallel output configurations, just as they do to the standard 4-LED application circuit. POWER DISSIPATION The maximum allowable power dissipation that this package is capable of handling can be determined as follows: P DMax =(TJMax -TA)/ θ JA Where T JMAX is the maximum junction temperature, TA is the ambient temperature, and θ JA is the junction-to-ambient thermal resistance of the specified package. The LM3595 come in the LLP-10 package that has a junction-to-ambient thermal resistance ( θ JA) equal to 55˚C/W. This value of θ JA is highly dependant upon the layout of the PC board (See the PCB Layout Considerations section of this datasheet for more information). The actual power dissipated by the LM3595 follows the equation: P DISS=(VINxIIN) - N(VOUTX xIOUTX) Where N equals the number of active outputs, V OUTX is the LED forward voltage, and I OUTX is the current supplied to the 20072215 FIGURE 1. Two Parallel Connected LEDs 20072216 FIGURE 2. One Parallel Connected LED www.national.com 9 |
类似零件编号 - LM3595 |
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类似说明 - LM3595 |
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