LTC3454
5
3454fa
LED Power Effi ciency vs LED CurrentOscillator Frequency vs Temperature
TEMPERATURE (°C)
–55
900
FREQUENCY (kHz)
920
960
980
1000
1100
1040
–15
25
45 125
3454 G16
940
1060
1080
1020
–35 5
65
85
105
V
OUT
= 3V
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 5.5V
V
IN
= 4.2V
I
LED
(mA)
100
EFFICIENCY (%)
80
85
90
900
3454 G17
75
70
60
300
500
700
200 1000
400
600
800
65
100
95
V
IN
= 3.6V
T
A
= 25°C
EFFICIENCY = (V
OUT
– V
LED
)I
LED
/V
IN
I
IN
FRONT PAGE APPLICATION
EN1 (Pin 1): Enable Input Pin for I
SET1
Current.
EN2 (Pin 2): Enable Input Pin for I
SET2
Current.
I
SET1
(Pin 3): LED Current Programming Pin. A resistor
to ground programs the current through the LED to I
LED
= 3850(0.8V/R
ISET1
). This amount of current adds to any
amount set by EN2/I
SET2
if used.
I
SET2
(Pin 4): LED Current Programming Pin. A resistor
to ground programs the current through the LED to I
LED
= 3850(0.8V/R
ISET2
). This amount of current adds to any
amount set by EN1/I
SET1
if used.
LED (Pin 5): Low Dropout Output for LED Current Biasing.
Connect the LED between V
OUT
and the LED pin.
SW2 (Pin 6): Switching Node. External inductor con-
nects between SW1 and SW2. Recommended value is
4.7μH/5μH.
V
OUT
(Pin 7): Buck-Boost Output Rail. Bypass to GND with
a ceramic capacitor. Recommended value is 10μF.
V
C
(Pin 8): Compensation Point for the Internal Error
Amplifi er Output. Connect a ceramic capacitor from V
C
to GND. Recommended value is 0.1μF.
V
IN
(Pin 9): Voltage Input Supply Pin (2.7V ≤ V
IN
≤ 5.5V).
Bypass to GND with a ceramic capacitor. Recommended
value is 10μF.
SW1 (Pin 10): Switching Node. External inductor con-
nects between SW1 and SW2. Recommended value is
4.7μH/5μH.
Exposed Pad (Pin 11): Ground Pin. Solder to PCB ground
for electrical contact and optimal thermal performance.
Output Voltage Ripple
Back Page Application
20mV/DIV
500ns/DIVV
IN
= 3.6V
I
LED
= 500mA
3454 G19
Start-Up Transient
Back Page Application
0V, 0A
CH1, V
OUT
1V/DIV
CH2, I
LED
500mA
FINAL VALUE
CH3, V
EN1
1V/DIV
0V
5ms/DIVV
IN
= 3.6V
I
LED
= 500mA
3454 G19
TYPICAL PERFORMANCE CHARACTERISTICS
PIN FUNCTIONS
