LM3530 datasheet(18/50 Pages) TI1

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BRT

LED

LED =

20.2 mA

mA x 0.8976

BRT

LED

LED =

10.9 mA

mA x 0.48438

BRT

LED

LED =

LM3530

SNVS606L – JUNE 2009 – REVISED DECEMBER 2014

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Example: PWM + I2C-Compatible Current Control:

As an example, assume the the General Configuration Register is loaded with (0x2D). From Table 5, this sets up

the LM3530 with:

Simple Enable OFF (bit 7 = 0)

Positive PWM Polarity (bit 6 = 0)

PWM Enabled (bit 5 = 1)

Full-Scale Current set at 15.5 mA (bits [4:2] = 100)

Brightness Mapping set for Exponential (bit 1 = 0)

Device Enabled via I2C (bit 0 = 1)

Next, the Brightness Control Register is loaded with 0x73. This sets the LED current to 51.406% of full scale (see

Equation 1). Finally, the PWM input is driven with a 0-V to 2-V pulse waveform at 70% duty cycle. The LED

current under these conditions will be:

where

•

BRT is the percentage of ILED_FS as set in the Brightness Control Register

(1)

8.3.12 I2C-Compatible Current Control Only

I2C-Compatible Control is enabled by writing a '1' to the I2C Device Enable bit (bit [0] of the General

Configuration Register), a '0' to the Simple Enable bit (bit 7), and a '0' to the PWM Enable bit (bit 5). With bit 5 =

0, the duty cycle information at the PWM input is not used in setting the LED current.

In this mode the LED current is a function of the Full-Scale LED current bits (bits [4:2] of the General

Configuration Register) and the code in the Brightness Control Register. The LED current mapping for the

Brightness Control Register can be linear or exponential depending on bit [1] in the General Configuration

Full-Scale LED Current bits and the Brightness Control Register code provides nearly 1016 possible current

levels selectable over the I2C-compatible interface.

Example: I2C-Compatible Current Control Only:

As an example, assume the General Configuration Register is loaded with 0x15. From Table 5 this sets up the

LM3530 with:

Simple Enable OFF (bit 7 = 0)

Positive PWM Polarity (bit 6 = 0)

PWM Disabled (bit 5 = 0)

Full-Scale Current set at 22.5mA (bits [4:2] = 101)

Brightness Mapping set for Exponential (bit 1 = 0)

Device Enabled via I2C (bit 0 = 1)

The Brightness Control Register is then loaded with 0x72 (48.438% of full-scale current from Equation 2). The

LED current with this configuration becomes:

where

•

BRT is the % of ILED_FS as set in the Brightness Control Register.

(2)

Next, the brightness mapping is set to linear mapping mode (bit [1] in General Configuration Register set to 1).

Using the same Full-Scale current settings and Brightness Control Register settings as before, the LED current

becomes:

(3)

Which is higher now since the code in the Brightness Control Register (0x72) corresponds to 89.76% of Full-

Scale LED Current due to the different mapping mode given in Figure 34.

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