LTC3452 Datasheet, PDF (13/16 Pages) Linear Technology – Synchronous Buck-Boost MAIN/CAMERA White LED Driver

LTC3452
APPLICATIO S I FOR ATIO
Although the LTC3452 can safely provide this current
continuously, the external LED(s) may not be rated for this
high a level of continuous current. Higher current levels in
a single LED are generally reserved for pulsed applica-
tions, such as LED camera flash. This is accomplished by
programming a high current with one or both of the R_ISET
resistors and pulsing the appropriate enable pin or pins as
shown in the back page application.
Varying LED Brightness Linearly
Continuously variable LED brightness control can be
achieved by interfacing directly to one or both of the I_SET
pins. Figure 3 shows four such methods employing a
voltage DAC, a current DAC, a simple potentiometer or a
PWM input applied to the I_SETL pin for controlling the low
power bank LED currents. These four techniques can be
similarly applied to the I_SETH pin for controlling the high
power bank LED currents.
V_IN
V_OUT
V_IN
V_OUT
VOLTAGE
DAC
EN_L
LED_L1
LTC3452
I_SETL
LED_L5
R_SET ≥ R_MINL
I_LED
=
256
0.8V – V_DAC
R_SET
V_DAC
(3a)
V_IN
V_OUT
CURRENT
DAC
EN_L
LED_L1
LTC3452
I_SETL
LED_L5
0.8V
IDAC ≤ _RMINL
I_LED = 256 • IDAC
(3b)
V_IN
V_OUT
EN_L
LED_L1
LTC3452
I_SETL
LED_L5
R_MINL
0.8V
I_LED = 256 _{RMINL + RPOT}
R_POT
(3c)
R_SET
100
EN_L
LED_L1
LTC3452
I_SETL
LED_L5
R_SET ≥ R_MINL
V_PWM
1µF
I_LED
=
256
0.8V – V_PWM
R_SET
=
256
0.8V
–
(DC% •
R_SET
V_DVCC)
DV_CC
f_PWM ≥ 10kHz
(3d)
3452 F03
Figure 3. Additional Brightness Control Methods: (3a) Using Voltage DAC,
(3b) Using Current DAC, (3c) Using Potentiometer, (3d) Using PWM Input
3452f
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