LM3533 datasheet(17/63 Pages) TI1

17 / 63 page

LM3533

www.ti.com

SNOSC68C – APRIL 2012 – REVISED SEPTEMBER 2015

Device Functional Modes (continued)

7.4.4.2 Run-Time Ramp

Current ramping from one brightness level to the next is programmed via the Run-Time Transition Time Register

(see Table 5). There are 8 different ramp-up times and 8 different ramp-down times. The ramp-up time can be

programmed independently from the ramp-down time, but each Control Bank cannot be independently

programmed. For example, programming a ramp-up or ramp-down time is a global setting for all Control Banks.

7.4.5 Brightness Register Current Control

For simple user-adjustable current control, the LM3533 features Brightness Register Current Control. This mode

is selected via the Control Bank Brightness Configuration Registers (see Table 8 and Table 10). Once set for

Brightness Register Current Control, the LED current is set by writing directly to the appropriate Control Bank

Brightness Registers (see Table 28). In this mode the current for a particular Control Bank becomes a function of

the full-scale LED current, the 8-bit code in the respective brightness register, and the PWM input duty cycle (if

PWM is enabled). The Control Bank Brightness Register contains an 8-bit code which represents the percentage

of the full-scale LED current. This percentage of full-scale current is different depending on the selected mapping

mode (see LED Current Mapping Modes).

7.4.6 PWM Control

The LM3533 device’s PWM input can be enabled for any of the Control Banks (see Table 7). Once enabled, the

LED current becomes a function of the code in the Control Bank Brightness Configuration Register and the PWM

input-duty cycle.

The PWM input accepts a logic level voltage and internally filters it to an analog control voltage. This results in a

linear response of duty cycle to current, where 100% duty cycle corresponds to the programmed brightness code

multiplied by the Full-Scale Current setting.

7.4.6.1 PWM Input Frequency Range

The usable input frequency range for the PWM input is governed on the low end by the cutoff frequency of the

internal low-pass filter (540 Hz, Q = 0.33) and on the high end by the propagation delays through the internal

logic. For frequencies below 2 kHz the current ripple begins to become a larger portion of the DC LED current.

Additionally, at lower PWM frequencies the boost output voltage ripple increases, causing a non-linear response

from the PWM duty cycle to the average LED current due to the response time of the boost. For the best

response of current vs. duty cycle, the PWM input frequency must be kept between 2 kHz and 100 kHz.

7.4.6.2 PWM Input Polarity

The PWM Input can be set for active low polarity, where the LED current is a function of the negative duty cycle.

This is set via the OVP/Boost Frequency/PWM Polarity Register (see Table 20).

7.4.7 ALS Current Control

The LM3533 features Ambient Light Sensor (ALS) current control which allows the LED current to be

automatically set based upon the received ambient light. To implement ambient light current control the LM3533

uses a 5 brightness zone implementation with 3 sets of Zone Targets.

7.4.7.1 ALS Brightness Zones (Zone Boundaries)

The LM3533 provides for a 5 brightness zone ambient light sensor interface. This allows for the LED current in

any current sink to change based upon which zone the received ambient light falls into. The brightness zones are

configured via 4 ALS Zone Boundary High and 4 ALS Zone Boundary Low Registers. Each Zone Boundary

mapping from the ALS Brightness Zone to the target backlight current.

Submit Documentation Feedback

Product Folder Links: LM3533

LM3533 Datasheet(PDF) 17 Page - Texas Instruments

LM3533 Datasheet(HTML) 17 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63

Datasheet Download

Link URL