LTC3206EUF Linear Technology, LTC3206EUF Datasheet - Page 14

• Manufacturer Part Number: LTC3206EUF
• Description: IC LED DRVR WT/RGB BCKLGT 24-QFN
• Manufacturer: Linear Technology
• Type: Backlight, White LED, RGB (I²C Interface)r

Specifications of LTC3206EUF

• Topology: PWM, Step-Up (Boost), Switched Capacitor (Charge Pump)
• Number Of Outputs: 11
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: RGB, White LED
• Frequency: 680kHz ~ 1.36MHz
• Voltage - Supply: 2.7 V ~ 4.5 V
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 400mA
• Internal Switch(s): Yes
• Efficiency: 92%
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -

APPLICATIO S I FOR ATIO
LTC3206
Once an LED pin drops out, the LTC3206 switches into
step-up mode. Employing the fractional ratio 1.5x charge
pump, the LTC3206 provides more efficiency than would
be achieved with a voltage doubling charge pump.
In 1.5x boost mode, the efficiency is similar to that of a
linear regulator with an effective input voltage of 1.5 times
the actual input voltage. This is because the input current
for a 1.5x fractional charge pump is approximately 1.5
times the load current. In an ideal 1.5x charge pump, the
power efficiency would be given by:
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3206.
If the junction temperature increases above approximately
160°C the thermal shutdown circuitry will automatically
deactivate the output. To reduce the maximum junction
temperature, a good thermal connection to the PC board
is recommended. Connecting the PGND pin (exposed
center pad) to a ground plane and maintaining a solid
ground plane under the device can reduce the thermal
resistance of the package and PC board considerably.
Brightness Control
Although the LTC3206 has many exponentially spaced
brightness settings for the main and sub displays, it is
possible to control the brightness by alternative means.
Figure 8 shows an example of how an external voltage
source can be use to inject a current into the I
pins to control brightness. For example, if R1 and R2 are
24k, then the LED current would range from 20mA to 0mA
as V
Alternatively, if only digital outputs are available, the
number of settings can be doubled from 15 to 30 by simply
14
η
CNTRL
IDEAL
≡
is swept from 0V to 1.2V.
P
P
LED
IN
=
U
V
V
IN
LED LED
• .
U
1 5
•
I
I
LED
≅
W
1 5
V
.
LED
V
IN
MS
U
or I
RGB
ing a PWM signal to the I
shown in Figure 10. The signal should range from 0V (full
on) to any voltage above 0.7V (full off).
Figure 10. PWM Brightness Control of the MAIN and SUB Displays
connecting V
extended to any number of bits and can also be applied to
the RGB display.
Finally, PWM brightness control can be achieved by apply-
Figure 8. Alternative Linear Brightness Control
Figure 9. Alternative Digital Brightness Control
LTC3206
LTC3206
LTC3206
CNTRL
I
I
RGB
I
RGB
I
I
MS
RGB
MS
I
MS
to a digital signal. This topology can be
11
12
11
12
11
12
I
LED
12k
12k
12k
12k
= 400
MS
(
R1
0.6V
||
R1
18.2k
R2
programming resistor as
3206 F08
3206 F09
3206 F10
34k
R2
PWM SIGNAL
0V TO 0.7V OR HIGHER
BRIGHTNESS = 1 – D
–
V
CNTRL
R2
)
V
V
0V TO 0.7V
OR HIGHER
CNTRL
DIG
3206f