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A8513 Datasheet(PDF) 11 Page - Allegro MicroSystems |
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A8513 Datasheet(HTML) 11 Page - Allegro MicroSystems |
11 / 24 page Wide Input Voltage Range, High Efficiency Fault Tolerant LED Driver A8513 11 Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com ISET pin. The limitation of this form of dimming is that the inter- nal ISET error amplifier is designed to work from 40 to 160 μA, thus limiting the dimming ratios that can be achieved. Figure 7, top panel is a typical application using a DAC to control the LED current using a single resistor connected to the ISET pin. The ISET current is controlled by the following formula: ISET = VISET – VDAC RISET (3) Where VISET is the ISET pin voltage and VDAC is the DAC out- put voltage. When the DAC voltage is equal to VISET, the internal reference, there is no current through RISET. When the DAC voltage starts to decrease, the ISET current starts to increase, thus increasing the LED current. When the DAC voltage is 0 V, the LED current will be at its maximum. • For a dual-resistor configuration (lower panel of figure 7), the ISET current is controlled by the following formula: ISET = – VISET RISET VDAC – VISET R1 (4) The advantage of this circuit is that the DAC voltage can be higher or lower, thus adjusting the LED current to a higher or lower value of the preset LED current set by the RISET resistor: ▫ VDAC = 1.003 V; the output is strictly controlled by RISET ▫ VDAC > 1.003 V; the LED current is reduced ▫ VDAC < 1.003 V; the LED current is increased Output Overvoltage Protection (OVP) and Output Undervoltage Protection (UVP) The A8513 has output overvoltage protection (OVP), output undervoltage protection and secondary overvoltage protection (open diode). Overvoltage Protection The OVP pin has a threshold, VOVPHI(th), of 1.218 V. A resistive divider can be used to set the VOUT over- voltage protection threshold up to 45 V (see figure 8). There is no restriction on the value of the resistor chosen, but it is recom- mended that the divider current be kept between 10 and 60 μA. This will minimize the effect of sense current on the accuracy of OVP, and minimize output voltage bleed-off during PWM dim- ming. Formulas for calculating the OVP resistor voltage divider are shown below. ROVP1 = (VOVP – 1.218 V) / ISET (5) ROVP2 = 1.218 V / ISET (6) The OVP function is not inherently a latched fault. If the OVP condition occurs during a load dump, the IC will stop switching but not shut down. Figure 7. Simplified diagram of voltage LED current control (upper) single resistor, and (lower) dual resistors. Figure 8. Simplified diagram of the OVP pin functions. GND DAC VDAC GND A8513 ISET GND DAC VDAC GND A8513 ISET RISET R1 RISET OVP VOUT ROVP1 ROVP2 A8513 1.218 V 100 mV |
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