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What should be considered when using a resistor on a short LED chain?

What should be considered when using a resistor on a short LED chain?

Infineon_Team
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Employee
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LITIX™ Basic+ includes in its portfolio devices with more than 1 output channels. If some of the channels are requiring less number of LEDs comparing to the others, it is recommended to place a resistor on the short LED chain.

In case that a resistor is placed on the short LED chain, as shown below:

Image1.png

Figure 1: Resistor on short LED chain

We need to pay attention, as it impacts the operation of the LITIXTM Basic+ in the following ways:

  • During high temperature conditions, the LITIXTM Basic+ reduces the output current. When the output current is reduced, the voltage drop across the output stage increases, causing more power dissipation. This further reduces the current causing a potentially unintended shutdown condition.
  • Increasing the resistance in the output current path, cause decreasing on the phase margin and stability of the control loop. The resistor value needs to be below 75 Ohms and the output wire length below 0.5 m. In that way the phase margin is maintained above 60°.
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