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LM3697 Datasheet(PDF) 15 Page - Texas Instruments

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Part No. LM3697
Description  High-Efficiency Three-String White LED Driver
Download  36 Pages
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Manufacturer  TI1 [Texas Instruments]
Direct Link  http://www.ti.com
Logo TI1 - Texas Instruments

LM3697 Datasheet(HTML) 15 Page - Texas Instruments

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BRIGHTNESS CODE
1Mhz Eff - 500Khz Eff, 4.7uH, Three String
(Negative values when 500Khz more efficient)
C002
1Mhz LED Eff > 500Khz LED Eff
500Khz LED Eff > 1Mhz LED Eff
Auto-Frequency
Threshold = 0x6C
LM3697
www.ti.com
SNOSCS2A – NOVEMBER 2013 – REVISED DECEMBER 2013
Figure 45. Auto-Frequency LED Efficiency Improvement Illustration
Table 1 summarizes the general recommendations for Auto-Frequency Threshold setting vs Inductance values
and LED string configurations. These are general recommendations — the optimum Auto-Frequency Threshold
setting should be evaluated for each application.
Table 1. Auto-Frequency Threshold Settings
Three String
Two String
Inductor
Auto-Frequency
Peak Efficiency
Peak
Auto-Frequency
Peak Efficiency
Peak
Improvement
Configuration
Improvement
Configuration
Threshold
Threshold
4.7 µH
6C
2.20%
3p5s
AC
1.10%
2p6s
10 µH
74
1.70%
3p4s
B4
1.30%
2p5s
22 µH
7C
0.70%
3p3s
BC
0.70%
2p4s
Brightness Register Current Control
The LM3697 features Brightness Register Current Control for simple user-adjustable current control set by
writing directly to the appropriate Control Bank Brightness Registers. The current for Control Banks A & B is a
function of the full-scale LED current, the 11-bit code in the respective brightness register, and the PWM input
duty cycle (if PWM is enabled). The Control A/B brightness should always be written with LSB's first and MSB's
last. The preferred operating mode is to control the high-voltage LED brightness by setting the 3 LSB's to zero
and using only the upper 8 MSB's. In this mode the LM3697 will use the full 11-bit brightness code while ramping
the high-voltage LED brightness.
PWM Control
The LM3697's PWM input can be enabled for Control Banks A or B (see Table 14). 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.
Copyright © 2013, Texas Instruments Incorporated
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