LED2001PUR datasheet(17/42 Pages) STMICROELECTRONICS

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LED2001

Application notes

As a consequence, the LED equivalent circuit gives the

αLED(s) term correlating the output

voltage with the high impedance FB input:

Equation 14

6.5

Total loop gain

In summary, the open loop gain can be expressed as:

Equation 15

Example 1

Design specification:

VIN=12 V, VFW_LED=3.5 V, nLED= 2, rLED= 1.1 Ω, ILED= 4 A, ILED RIPPLE= 2%

The inductor and capacitor value are dimensioned in order to meet the ILED RIPPLE

specification (see Section 7.1.2 for output capacitor and inductor selection guidelines):

L=2.2

μH, COUT=2.2 μF MLCC (negligible ESR)

Accordingly, with Section 7.1.1 the sensing resistor value is:

Equation 16

Equation 17

The gain and phase margin Bode diagrams are plotted respectively in Figure 9 and

Figure 10.

LED nLED

()

SENSE

LED

SENSE

⋅

----------------------------------------------------------

()

CO s

() A

0 s

() α

LED nLED

()

⋅⋅

100 mV

--------------------

25 m

≅

LED nLED

()

SENSE

LED

SENSE

⋅

----------------------------------------------------------

25 m

21.1

⋅

25 m

----------------------------------------------

0.011

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