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LM3433 データシート(PDF) 9 Page - Texas Instruments |
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LM3433 データシート(HTML) 9 Page - Texas Instruments |
9 / 15 page 0.3V < VADJ < (The greater of 1.5V or (VIN - 1.9V)) VSENSE = (VADJ - VCGND)/16.66 RSENSE = 60mV/ILED ILED = VSENSE/RSENSE LM3433 www.ti.com SNVS535B – OCTOBER 2007 – REVISED MARCH 2008 The LED current is set by the voltage across a sense resistor. This sense voltage is nominally 60mV but can be programmed higher or lower by an external control voltage. The running frequency of the converter is programmed by an external RC network in conjunction with the LED's forward voltage. The frequency is nominally set around 200kHz to 500khz. Fast PWM control is available by shorting the output of the current source by a MOSFET in parallel with the LED. During the LED OFF time the running frequency is determined by the RC network and the parasitic resistance of the output circuit including the DIM FET RDSON. The LM3433 system has been evaluated to be a very accurate, high compliance current source. This is manifest in its high output impedance and accurate current control. The current is measured to vary less than 6mA out of 6A when transitioning from LED OFF (output shorted) to LED ON (output ~6V). PROTECTION The LM3433 has dedicated protection circuitry running during normal operation. The thermal shutdown circuitry turns off all power devices when the die temperature reaches excessive levels. The VCC undervoltage lockout (UVLO) comparator protects the power devices during power supply startup and shutdown to prevent operation at voltages less than the minimum operating input voltage. The VCC pin is short circuit protected to VEE. The LM3433 also features a shutdown mode which decreases the supply current to approximately 35µA. The ADJ, EN, and DIM pins are capable of sustaining up to +/-2mA. If the voltages on these pins will exceed either VIN or CGND by necessity or by a potential fault, an external resistor is recommended for protection. Size this resistor to limit pin current to under 2mA. A 10k resistor should be sufficient. This resistor may be used in any application for added protection without any impact on function or performance. DESIGN PROCEDURE This section presents guidelines for selecting external components. SETTING LED CURRENT CONTROL LM3433 uses average current mode control to regulate the current delivered to the LED (ILED). An external current sense resistor (RSENSE) in series with the LED is used to convert ILED into a voltage that is sensed by the LM3433 at the CSP and CSN pins. CSP and CSN are the inputs to an error amplifier with a programmed input offset voltage (VSENSE). VSENSE is used to regulate ILED based on the following equation: (1) FIXED LED CURRENT The ADJ pin sets VSENSE. Tie ADJ to VIN to use a fixed 60mV internal reference for VSENSE. Select RSENSE to fix the LED current based on the following equation: (2) ADJUSTABLE LED CURRENT When tied to an external voltage the ADJ pin sets VSENSE based on the following equation: (3) When the reference on ADJ is adjustable, VSENSE and ILED can be adjusted within the linear range of the ADJ pin. This range has the following limitations: (4) When VADJ is less than this linear range the VSENSE is guaranteed by design to be less than or equal to 0.3V/16.667. When VADJ is greater than this linear range and less than VIN - 1V, VSENSE is guaranteed by design to be less than or equal to VADJ/16.667. If VADJ is greater than VIN - 1V, VSENSE switches to 60mV. Copyright © 2007–2008, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM3433 |
同様の部品番号 - LM3433 |
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同様の説明 - LM3433 |
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