LM3697_15 Datasheet, PDF (31/43 Pages) Texas Instruments – High-Efficiency Three-String White LED Driver

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LM3697
SNOSCS2C – NOVEMBER 2013 – REVISED OCTOBER 2015
V_IN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , T_A = 25°C
unless otherwise specified. Efficiency is V_OUT × (I_HVLED1 + I_HVLED2 + I_HVLED3)/(V_IN × I_IN), matching curves are (ΔI_{LED_MAX}/I_{LED_AVE}).
25.00
20.00
15.00
10.00
5.00
Max
Typ
Min
0.00
Figure 54. Response To Step Change In PWM Input Duty
Cycle
PWM DUTY CYCLE (%)
C001
Figure 55. HVLED Current Vs PWM Input Duty Cycle
Figure 56. Line Step Response
8.3 Initialization Set Up
Table 25 illustrates the minimum number of register writes required for a two-parallel, seven-series LED
configuration. This example uses the default settings for ramp times (2048 µsec), mapping mode (exponential)
and full-scale current (20.2 mA). In this mode of operation the LM3697 controls the brightness LSB's to ramp
between the 8-bit MSB brightness levels providing 11-bit dimming while requiring only 8-bit commands from the
host controller.
Table 25. Control Bank A, 8-Bit Control, Two-String, Seven Series LED Configuration Example
REGISTER NAME
HVLED Current Sink Output
Configuration
HVLED Current Sink Feedback
Enables
Boost Control
Control Bank Enables
Control A Brightness LSB
Control A Brightness MSB
ADDRESS
0x10
0x19
0x1A
0x24
0x20
0x21
DATA
0x04
0x03
0x04
0x01
0x00
User Value
DESCRIPTION
HVLED1 & 2 assigned to Control Bank A
Enable feedback on HVLED1 & 2, disable feedback on HVLED3
OVP = 32V, ƒ_sw = 500 kHz
Enable Control Bank A
Control A Brightness LSB written only once
Control A Brightness MSB updated as required
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