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LM3430 Scheda tecnica(PDF) 5 Page - National Semiconductor (TI) |
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LM3430 Scheda tecnica(HTML) 5 Page - National Semiconductor (TI) |
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5 / 16 page  Connect Power Supply to the Demonstration Board Input supply voltage, V IN is connected to the VIN and GND solder pads of the demonstration board. V IN ranges from 8V to 21V. Once the power is applied, all LEDs on the LED panel will be lighted up. The default setting of the demonstration board is in analog dimming mode, by adjusting the poten- tiometer, VR1; the LED brightness can be adjusted accord- ingly. For some cases, due to the incorrect power-up sequence tim- ing of the LM3430 and the LM3432, some strings may have problem at cold start-up and the LM3432's fault detect may be falsely triggered. The normal operation can be recovered by shorting JP2 for few mini-seconds to reset the LM3432's fault detect circuit. This condition only happens when the board is powered up with LEDs in maximum brightness. This condition is not common in most backlighting applications. Typical applications normally have some sort of power-up se- quence control to make sure the high voltage supply from the LM3430 is available before the LM3432 is being enabled. Synchronization of the Multiple Boost Converters In certain applications, more than one LED rail voltages are required in a single system. For example, a RGB backlighting system requires at least two different LED rail voltages, one for RED and one for BLUE and GREEN. Multiple switching converters running at slightly different switching frequency can introduce complex EMI situation. In order to accommo- date this problem, the LM3430 can be synchronized to an external master clock that drives all boost converters switch- ing at one single frequency. The external clock must running at a higher frequency than the preset free running oscillator frequency, i.e. > 1 MHz with this demonstration board. This feature can be enabled by applying external synchronization signal to CN3; the device will pass the control to the external synchronization signal automatically. Dynamic Headroom Control With the LM3432's VDHC output pin connected to LM3430's VDHC input pin through a gain setting resistor (R19), the Dy- namic Headroom Control (DHC) function will be in operation. The LM3432's DHC function will interact with the LM3430 to adjust the boost converter output voltage, VLED to LED strings just enough to keep all LED strings current in regula- tion. This minimum headroom voltage across the LED strings guarantees the best achievable system efficiency. LED OPEN and SHORT Fault Indication The LM3432 has the ability to detect both OPEN and SHORT faults of LEDs string by string. Whenever a fault is detected, the respective LED string will be latched OFF to protect the device from any possible damage and a signal will be issued to communicate with system micro-controller for appropriate actions. The SHORT fault detect threshold is 7.9V (typical) across IOUT pin to ground and OPEN fault check for zero sink current in any channel for more than 50 µs during ON duty. The fault output, FAULTb pin is connected to an indicator LED in the demonstration board. Over-Temperature Monitor and Shutdown If the on-die temperature is over 125°C, the OTMb pin will be pulled to ground to inform the system micro-controller for im- mediate attention. Corrective action is expected to lower the die temperature, for example, the system can reduce the PWM duty factor to lower the average current into the IOUTs. If the on-die temperature rises further to 165°C, the LM3432 will shutdown all channels to prevent any potential damage to the device. When the device is cooled down to about 145°C, normal operation will resume. Again, in the demonstration board, the over-temperature signal output, OTMb pin is con- nected to an indicator LED. 5 www.national.com |
Codice articolo simile - LM3430_07 |
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Descrizione simile - LM3430_07 |
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