LTC3206EUF#TR Linear Technology, LTC3206EUF#TR Datasheet - Page 13

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

Specifications of LTC3206EUF#TR

• 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
Table 4 shows a list of ceramic capacitor manufacturers
and how to contact them:
Table 4. Recommended Capacitor Vendors
AVX
Kemet
Murata
Taiyo Yuden
Vishay
For very light load applications, the flying capacitors
may be reduced to save space or cost. The theoretical
minimum output resistance of a 1.5x fractional charge
pump is given by:
where f
C
charge pump will typically be weaker than the theoretical
limit due to additional switch resistance, however for very
light load applications, the above expression can be used
as a guideline in determining a starting capacitor value.
Layout Considerations and Noise
Due to its high switching frequency and the transient
currents produced by the LTC3206, careful board layout is
necessary. A true ground plane and short connections to
all capacitors will improve performance and ensure proper
regulation under all conditions. Figure 7 shows the recom-
mended layout configuration.
The flying capacitor pins C1
very high edge rate waveforms. The large dv/dt on these pins
can couple energy capacitively to adjacent printed circuit
board runs. Magnetic fields can also be generated if the
flying capacitors are not close to the LTC3206 (i.e., the loop
area is large). To decouple capacitive energy transfer, a
Faraday shield may be used. This is a grounded PC trace
between the sensitive node and the LTC3206 pins. For a high
quality AC ground, it should be returned to a solid ground
plane that extends all the way to the LTC3206.
FLY
R
OL MIN
is the value of the flying capacitors. Note that the
(
OSC
)
is the switching frequency (960kHz typ) and
≡
1 5
.
V
U
IN
I
OUT
–
V
OUT
U
+
, C2
www.avxcorp.com
www.kemet.com
www.murata.com
www.t-yuden.com
www.vishay.com
=
2
+
f
, C1
OSC FLY
W
1
C
–
and C2
U
–
will have
Power Efficiency
To calculate the power efficiency (η) of a white LED driver
chip, the LED power should be compared to the input
power. The difference between these two number repre-
sents lost power whether it is in the charge pump or the
current sources. Stated mathematically, the power effi-
ciency is given by:
The efficiency of the LTC3206 depends upon the mode in
which it is operating. Recall that the LTC3206 operates as
a pass switch, connecting V
drops out. This feature provides the optimum efficiency
available for a given input voltage and LED forward volt-
age. When it is operating as a switch, the efficiency is
approximated by:
since the input current will be very close to the LED
current.
At moderate to high output power, the quiescent current
of the LTC3206 is negligible and the expression above is
valid. For example, with V
and V
which is very close to the theoretical 92.3% calculation.
η ≡
η ≡
LED
P
P
P
P
LED
LED
Figure 7. Optimum Single Layer PCB Layout
equal to 3.6V, the measured efficiency is 92.2%,
IN
IN
PIN 1
=
V
LED
V
IN
•
•
I
I
LED
IN
IN
≅
IN
= 3.9V, I
V
to CPO until one of the LEDs
V
LED
IN
OUT
LTC3206
= 20mA • 6 LEDs
13
3206 F07
3206f
V
CPO
GND
IN