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LTM8005 Datasheet(PDF) 10 Page - Linear Technology |
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LTM8005 Datasheet(HTML) 10 Page - Linear Technology |
10 / 26 page LTM8005 10 8005f For more information www.linear.com/LTM8005 OPERATION The LTM8005 is a stand-alone non-isolated switching DC/ DC regulator intended for LED driver applications. This µModule power converter provides a regulated current from an input voltage range of 5V to 38V, and up to 38V output. A simplified block diagram is provided in the pre- vious section. The LTM8005 is equipped with a ground referred power switch and a power rectifier. Connect external power devices, such as an inductor, to these pins to implement boost, buck-boost mode, buck mode or SEPIC topologies to drive a string of LEDs. The LTM8005 features an integrated sense resistor to control the LED current. The maximum regulated current is 1.6A, and this can be reduced by applying a voltage less than 1.2V to the CTRL1 or CTRL2 pins. The output current is reported by the voltage on the ISMON pin. The LTM8005 also features an integrated PMOS discon- nect switch to implement PWM dimming that is controlled by a signal on the PWM pin. The PMOS also disconnects the LEDs during fault conditions. If input current limiting is desired, apply an external sense resistor to the IVINP and IVINN pins. The full input current will flow through this external sense resistor, so choose a resistor with an appropriate power rating. The LTM8005 will start to decrease the power if the voltage between the IVINP and INVINN pins exceeds 60mV. A 10nF capacitor is provided internally to compensate the input current regulation loop, but additional capacitance may be added externally to further filter the voltage at the IVINCOMP pin. The LTM8005 features spread spectrum frequency modulation, which causes the switching frequency to modulate to a frequency that is approximately 70% of the programmed value set by the RT resistor. This modu- lation decreases the energy emitted at a single frequency, reducing the EMI amplitude. The modulation behavior is set by a capacitor on the RAMP pin to GND. Input voltage turn-on and turn-off thresholds are set by resistor networks at the EN/UVLO and OVLO pins. Applying a voltage of greater than 1.24V to the EN/UVLO pin enables the part. OPENLED and SHORTLED are active low open drain sta- tus bits that indicate an open LED or shorted LED condi- tion. OPENLED transitions to a logic low when the FB pin rises above 1.2V and the LED current decreases below 160mA. SHORTLED transitions to a logic low when the FB pin falls below 300mV or the LED current exceeds 2.4A. Further details on these and other functions are given in the Applications Information section. An external soft start capacitor at the SS pin minimizes the current spike that occurs at start up and the SS pin also programs hiccup or latchoff mode fault protection. The LTM8005 is equipped with a thermal shutdown that inhibits power switching at high junction temperatures. The activation threshold of this function is above the abso- lute maximum temperature rating to avoid interfering with normal operation, so prolonged or repetitive operation under a condition in which the thermal shutdown activates may damage or impair the reliability of the device. |
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