AN2823

The L5973AD in LED driving applications

Doc ID 15015 Rev 1

17/33

Figure 17.

Phase plot

The cutoff frequency and the phase margin are:

Equation 18

2.1.4

LED current accuracy

The purpose of this paragraph is to estimate each contribution which affects the accuracy of

mW).

The current flowing in the LED satisfies the equation:

Equation 19

The accuracy

εL597x of the reference and feedback voltage of the embedded error amplifier

is ± 1.2% (see the L5973AD device datasheet). The two parameters are based on the

internal bandgap cell of the device, so the relative spread is minimized (they are in tracking).

The spread of the current flowing in the LED is expressed as:

Equation 20

AM01367v1

F

C

36kHz

=

ζ

M

=

I

LED

R

SENSE

V

S

V

FB

R

6

R

1

-------

V

REF

V

FB

–

()

⋅

–

=

=

⋅

I

LED

V

FB

1

ε

L597x

±

()

⋅

R

6

1

ε

R

6

±

()

⋅

R

1

1

ε

R

1

±

()

⋅

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

V

REF

V

FB

–

() 1 ε

L597x

±

()

⋅⋅

–

R

SENSE

1

ε

R

SENSE

±

()

⋅

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

=