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AS1116 Datasheet(PDF) 18 Page - ams AG |
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AS1116 Datasheet(HTML) 18 Page - ams AG |
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18 / 24 page  www.austriamicrosystems.com/LED-Driver-ICs/AS1116 Revision 1.08 17 - 23 AS1116 Datasheet - Ty p i c a l A p p l i c a t i o n 9 Typical Application Selecting RSET Resistor Value and Using External Drivers Brightness of the display segments is controlled via RSET. The current that flows between VDD and ISET defines the current that flows through the LEDs. Segment current is about 200 times the current in ISET. Typical values for RSET for different segment currents, operating voltages, and LED volt- age drop (VLED) are given in Table 21 & Table 22. The maximum current the AS1116 can drive is 47mA. If higher currents are needed, exter- nal drivers must be used, in which case it is no longer necessary that the devices drive high currents. Note: The display brightness can also be logically controlled (see Intensity Control Register (0x0A) on page 15). Calculating Power Dissipation The upper limit for power dissipation (PD) for the AS1116 is determined from the following equation: PD = (VDD x 5mA) + (VDD - VLED)(DUTY x ISEG x N) (EQ 1) Where: VDD is the supply voltage. DUTY is the duty cycle set by intensity register (page 15). N is the number of segments driven (worst case is 8) VLED is the LED forward voltage ISEG = segment current set by RSET Dissipation Example: ISEG = 40mA, N = 8, DUTY = 15/16, VLED = 2.2V at 40mA, VDD = 5V (EQ 2) PD = 5V(5mA) + (5V - 2.2V)(15/16 x 40mA x 8) = 0.865W (EQ 3) Thus, for a QSOP-24 package ΘJA = +88°C/W, the maximum allowed TAMB is given by: TJ,MAX = TAMB + PD x ΘJA = 150°C = T AMB + 0.865W x 88°C/W (EQ 4) In this example the maximum ambient temperature must stay below 73.88°C. Table 21. RSET vs. Segment Current and LED Forward Voltage, VDD = 2.7V & 3.3V & 3.6V ISEG (mA) VLED VLED VLED 1.5V 2.0V 1.5V 2.0V 2.5V 1.5V 2.0V 2.5V 3.0V 40 5k Ω 4.4k Ω 6.7k Ω 6.4k Ω 5.7k Ω 7.5k Ω 7.2k Ω 6.6k Ω 5.5k Ω 30 6.9k Ω 5.9k Ω 9.1k Ω 8.8k Ω 8.1k Ω 10.18k Ω 9.8k Ω 9.2k Ω 7.5k Ω 20 10.7k Ω 9.6k Ω 13.9k Ω 13.3k Ω 12.6k Ω 15.6k Ω 15k Ω 14.3k Ω 13k Ω 10 22.2k Ω 20.7k Ω 28.8k Ω 27.7k Ω 26k Ω 31.9k Ω 31k Ω 29.5k Ω 27.3k Ω Table 22. RSET vs. Segment Current and LED Forward Voltage, VDD = 4.0V & 5.0V ISEG (mA) VLED VLED 1.5V 2.0V 2.5V 3.0V 3.5V 1.5V 2.0V 2.5V 3.0V 3.5V 4.0V 40 8.6k Ω 8.3k Ω 7.9k Ω 7.6k Ω 5.2k Ω 11.35k Ω 11.12kΩ 10.84kΩ 10.49kΩ 10.2kΩ 9.9kΩ 30 11.6k Ω 11.2k Ω 10.8k Ω 9.9k Ω 7.8k Ω 15.4k Ω 15.1k Ω 14.7k Ω 14.4k Ω 13.6k Ω 13.1kΩ 20 17.7k Ω 17.3k Ω 16.6k Ω 15.6k Ω 13.6kΩ 23.6k Ω 23.1k Ω 22.6k Ω 22k Ω 21.1k Ω 20.2kΩ 10 36.89k Ω 35.7k Ω 34.5k Ω 32.5k Ω 29.1kΩ 48.9k Ω 47.8k Ω 46.9k Ω 45.4k Ω 43.8k Ω 42k Ω |
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