ST1CC40 datasheet(15/37 Pages) STMICROELECTRONICS

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ST1CC40

Application notes

The embedded compensation network is RC = 70 K, CC = 195 pF while CP and CO can be

considered as negligible. The error amplifier output resistance is 240 M

so the relevant

singularities are:

Equation 12

6.4

LED small signal model

Once the system reaches the working condition the LEDs composing the row are biased

and their equivalent circuit can be considered as a resistor for frequencies << 1 MHz.

The LED manufacturer typically provides the equivalent dynamic resistance of the LED

biased at different DC current. This parameter is required to study the behavior of the

system in the small signal analysis.

For instance, the equivalent dynamic resistance of Luxeon III Star from Lumiled measured

with a different biasing current level is reported below:

In case the LED datasheet doesn’t report the equivalent resistor value, it can be simply

derived as the tangent to the diode I-V characteristic in the present working point (see

Figure 7).

Figure 7. Equivalent series resistor

11 6 kHz



fP LF

34 Hz



rLED

1,3



ILED 350mA

0,9



ILED 700mA







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