LTC3453 LINER [Linear Technology], LTC3453 Datasheet - Page 10

• Manufacturer Part Number: LTC3453
• Description: Synchronous Buck-Boost High Power White LED Driver
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC3453
The unity-gain frequency of the error amplifier with the
Type I compensation is given by:
where g
1/5.2k) and C
V
capacitor value is recommended.
Paralleling LED Outputs for Higher Current
Two or more LED output pins can be connected together
in parallel to achieve higher output current in fewer than 4
LEDs. For a very high power LED such as a LumiLED, all
four outputs can be connected in parallel for maximum
total output current, as shown in the cover page applica-
tion of this datasheet.
Maximum LED Current
As described in the Operation section, the output LED
current with both enable pins logic high is equal to
10
Figure 3. Brightness Control Methods: (a) Using Voltage DAC, (b) Using Current DAC, (c) Using Potentiometer, (d) Using PWM Input
C
I
f
pin. For the white LED application, a 0.1µF or greater
LED
UG
=
= 384 [0.8V/(R
m
2 • •
is the error amp transconductance (typically
π
g
VC
m
C
is the external capacitor to GND at the
VC
U
VOLTAGE
DAC
ISET1
U
V
V
|| R
IN
IN
V
R
R
R
DAC
SET
MIN
POT
ISET2
ENx
I
ENx
I
SETx
SETx
≥ R
LTC3453
LTC3453
MIN
W
)]
LED1
LED4
(a)
LED1
LED4
(c)
I
I
LED
LED
= 384
= 384
V
V
OUT
OUT
U
0.8V – V
R
MIN
R
0.8V
SET
+ R
DAC
POT
Since the maximum continuous output current is limited
to 500mA, this sets a minimum limit on the parallel
combination of R
Although the LTC3453 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
are generally reserved for pulsed applications, such as
LED camera flash. This is accomplished by programming
a high current with one of the R
the appropriate enable pin.
Varying LED Brightness
Continuously variable LED brightness control can be
achieved by interfacing directly to one or both of the I
pins. Figure 3 shows four such methods employing a
voltage DAC, a current DAC, a simple potentiometer or a
PWM input. It is not recommended to control brightness
by PWMing the enable pins directly as this will toggle the
LTC3453 in and out of shutdown and result in erratic
operation.
CURRENT
DAC
R
= 2458Ω
MIN
R
100
SET
V
V
= (R
IN
IN
V
R
SET
PWM
IDAC ≤
1µF
ENx
I
ENx
I
SETx
SETx
≥ R
ISET1
LTC3453
LTC3453
MIN
R
0.8V
MIN
f
PWM
ISET1
|| R
LED1
LED4
LED1
LED4
≥ 5kHz
(b)
(d)
ISET2
I
I
LED
LED
and R
DV
= 384 • IDAC
= 384
= 384
CC
)|
V
V
OUT
OUT
0.8V – V
0.8V – (DC% • V
MIN
ISET2
R
SET
ISET
PWM
3453 F03
R
= 4(384[0.8V/500mA])
SET
equal to
resistors and pulsing
DVCC
)
3453fa
SET