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EUP2796JIR1 Datasheet(PDF) 7 Page - Eutech Microelectronics Inc |
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EUP2796JIR1 Datasheet(HTML) 7 Page - Eutech Microelectronics Inc |
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7 / 9 page  EUP2796 DS2796 Ver1.0 Feb. 2007 7 Application Information Enable Pins: ENM, ENS The EUP2796 has 2 enable pins-ENM and ENS, which control the main and sub LEDs. All two are active-high logic (HIGH = ON). When both of ENM or ENS voltage is low (<0.5V), the part is in shutdown mode. All internal circuitry is OFF and the part consumes almost no supply current when the EUP2796 is shutdown. When the voltage on either of ENM and ENS pin is high (>1.1V), the part is active. The charge pump is ON, and turn on the output currents to drive the LEDs. ENM activates /deactivates the four group-A outputs (D1-D4). ENS activates/deactivates the two group-B outputs (D5-D6). There is no pull down resistors that are connected internally between each of the enable pins to ground. Setting LED Currents The output currents of the EUP2796 can be set to a desired value simply by connecting an appropriately sized resistor (RSET) between the ISET pin of the EUP2796 and GND. The output currents (LED currents) are proportional to the current that flows out of the ISET pin. The output currents are a factor of 100 greater than the ISET current. The feedback loop of an internal amplifier sets the voltage of the ISET pin to 1.18V(typ.). Placing a resistor between ISET and GND programs the ISET current, and thus the LED currents. The statements above are simplified in the equations below: () SET SET DXX R V 00 1 I × × = () DXX SET I V 18 . 1 00 1 R × × = Maximum Output Current, Maximum LED Voltage, Minimum Input Voltage The EUP2796 can drive 6 LEDs at 15mA each from an input voltage as low as 3.0V, so long as the LEDs have a forward voltage of 3.6V or less (room temperature). The statement above is a simple example of the LED drive capabilities of the EUP2796. The statement contains the key application parameters that are required to validate an LED- drive design using the EUP2796: LED current (ILED), number of active LEDs (N), LED forward voltage (VLED), and mini- mum input voltage (VIN-MIN). The equation below can be used to estimate the total output current capability of the EUP2796: ()1 . eq , K R N V V 5 . 1 I HR OUT LED IN MAX _ LED + ∗ − ∗ = mA / mV 12 4 N V V 5 . 1 I LED IN MAX _ LED + Ω ∗ − ∗ = ROUT – Output resistance. This parameter models the internal losses of the charge pump that result in voltage droop at the pump output POUT. Since the magnitude of the voltage droop is proportional to the total output current of the charge pump, the loss parameter is modeled as a resistance. The output resistance of the EUP2796 is typically 4Ω (VIN = 3.0V, TA = 25˚C). In equation form: () 2 . eq R I N V 5 . 1 V OUT LED IN POUT × × − × = KHR – Headroom constant. This parameter models the minimum voltage required to be present across the current sources for them to regulate properly. This minimum voltage is proportional to the programmed LED current, so the constant has units of mV/mA. The typical KHR of the EUP2796 is 12mV/mA. In equation form: ( )( ) 3 . eq I K V V LED HR LED POUT × > − The "ILED-MAX" equation (eq. 1) is obtained from combining the ROUT equation (eq. 2) with the KHR equation (eq. 3) and solving for ILED. Maximum LED current is highly dependent on minimum input voltage and LED forward voltage. Output current capability can be increased by raising the minimum input voltage of the application, or by selecting an LED with a lower forward voltage. Excessive power dissipation may also limit output current capability of an application. |
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Similar Description - EUP2796JIR1 |
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