LM3633 datasheet(12/58 Pages) TI2

12 / 58 page

Outputs

(Assigned to Control banks)

Control

Banks

BANK A

Environmental

Stimulus

PWM

Control

Usable

Stimulus

BANK B

HVLED1

HVLED2

HVLED3

High-Voltage LED Assignment

Control Bank Configuration

Boost Converter Configuration

Startup/Shutdown Ramp Configuration

Run-Time Ramp Configuration

Brightness Control

I2C

Compatible

Interface

SDA

SCL

Internal Low Pass

Filter

PWM

HVLED1

HVLED2

HVLED3

LM3633

SNVS867 – JUNE 2014

www.ti.com

7.4 Device Functional Modes

7.4.1 High-Voltage LED Control

Figure 12. High-Voltage Functional Control Diagram

7.4.1.1 High-Voltage Boost Converter

The high-voltage boost converter provides power for the three high-voltage current sinks (HVLED1, HVLED2 and

HVLED3). The boost circuit operates using a 4.7-µH to 22-µH inductor and a 1-µF output capacitor. The

selectable 500-kHz or 1-MHz switching frequency allows for use of small external components and provides for

high boost-converter efficiency. HVLED1, HVLED2, and HVLED3 feature an adaptive current regulation scheme

where the feedback point (HVLED1, HVLED2, and HVLED3) regulates the LED headroom voltage to VHR_HV.

When there are different voltage requirements in the high-voltage LED strings (string mismatch), the LM3633

regulates the feedback point of the highest voltage string to VHR_HV and drops the excess voltage of the lower-

voltage string across the lower string(s) current sink.

7.4.1.2 High-Voltage Current Sinks (HVLED1, HVLED2 and HVLED3)

HVLED1, HVLED2, and HVLED3 control the current in the high-voltage LED strings as configured by Control

Bank A or Control Bank B. Each Control Bank has 5-bit full-scale current programmability and 11-bit brightness

control. High-voltage current sinks are assigned to a control bank through the HVLED Current Sink Output

Configuration register (see Table 5).

7.4.1.3 High-Voltage Current String Biasing

Each high-voltage current string can be powered from the LM3633 boost output (COUT) or from an external

source. The feedback enable bits (HVLED Current Sink Feedback Enables register bits [2:0]) determine where

the high-voltage current string anodes are connected. When set to '1' (default) the high-voltage current sink

inputs are included in the boost feedback loop. This allows the boost converter to adjust its output voltage to

maintain the LED headroom voltage VHR_HV at the current sink input.

When powered from alternate sources the feedback enable bits should be set to '0'. This removes the particular

current sink from the boost feedback loop. In these configurations the application must ensure that the headroom

voltage across the high-voltage current sink is high enough to prevent the current sink from going into dropout

(see the Figure 63 for data on the high-voltage LED current vs VHR_HV).

Setting the HVLED Current Sink Feedback Enables register bits also determines triggering of the shorted high-

voltage LED String Fault flag (see Fault Flags/Protection Features section).

Submit Documentation Feedback

Product Folder Links: LM3633

LM3633 Datasheet(PDF) 12 Page - Texas Instruments

LM3633 Datasheet(HTML) 12 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

Datasheet Download

Link URL