Cirrus-logic AN368 Manual de usuario descargar pdf (Pagina 23)

AN368

AN368REV2 23

h. Switching Frequency Across Dim Range

From the equations below and setting the OTP registers as follows, the switching frequency across the dim

range can be calculated. A sample plot of the switching frequency across dim values is shown in Figure 7.

The frequencies in regions A, B, C, and D are governed by Equations 44, 45, 46 and 47, respectively.

Transitions between connecting regions are the result of simple inequalities. The following four equations do

not include the effect of a color system. Equations 44 through 47 must be adjusted after the color system has

been designed.

Frequency in Region A

In Region A, the system operates in CRM, and the period TT

is calculated using Equation 44:

where,

> TT

at the given dim level

dim = The 12-bit dim level provided by the boost stage

Frequency in Region B

In Region B, the system operates in DCM, but the peak current remains the same. Period TT

is calculated

using Equation 45:

where,

< 50s

> TT

0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

Frequency (kHz)

Dim

Figure 7. Dual Pulses Switching Frequency

0.5 TT

dim1

dim2

+ TT

dim1

dim2

+

res

++

[Eq. 44]

dimx

2LdimI

MODEx

N

MODEx

1D

MODEx

–=

[Eq. 45]

FREQ

dim

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

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 79 80

Comentarios a estos manuales

Sin comentarios

Cirrus-logic AN368 Manual de usuario Pagina 23

Comentarios a estos manuales

Relacionado con productos y manuales para Hardware Cirrus-logic AN368