LTC3205EUF Linear Technology, LTC3205EUF Datasheet - Page 9

• Manufacturer Part Number: LTC3205EUF
• Description: IC LED DRVR WT/RGB BCKLGT 24-QFN
• Manufacturer: Linear Technology
• Type: Backlight, White LED, RGB (Serial Interface)r

Specifications of LTC3205EUF

• Topology: PWM, Step-Down (Buck), Step-Up (Boost), Switched Capacitor (Charge Pump)
• Number Of Outputs: 9
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: RGB, White LED
• Frequency: 600kHz ~ 1.1MHz
• Voltage - Supply: 2.8 V ~ 4.5 V
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 250mA
• Internal Switch(s): Yes
• Efficiency: 92%
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -

OPERATIO
Unused MAIN or SUB Display LED Pins
Any of the six white LED pins (MAIN1-MAIN4, SUB1 and
SUB2) can cause the LTC3205 to switch from 1:1 mode to
2:3 charge pump mode if they drop out. If an unused LED
pin is left unconnected or grounded, it will automatically
drop out and force the LTC3205 into charge pump mode.
To avoid this problem, unused LED pins on the MAIN and
SUB displays should be connected to CPO. However, power
is not wasted in this configuration. When the LED pin voltage
is within approximately 1V of CPO, its LED current is
switched off and only a small 10 A test current remains.
Figure 4 shows a block diagram of each of the MAIN and
SUB LED pins. The RED, GREEN and BLUE pins do not affect
the state of the charge pump so they can be left floating or
grounded if unused.
RGB Illuminator Drivers
The red, green and blue LEDs can be individually set to
have a duty cycle ranging from 0/15 (off) to 15/15 (full on)
with 1/15 increments in between. The combination of 16
possible brightness levels gives the RGB indicator LED a
APPLICATIO S I FOR ATIO
Interfacing to a Microcontroller
The serial port of the LTC3205 can be connected directly
to an MC68HC11 style microcontroller’s serial port. The
microcontroller should be configured as the master device
and its clock’s idle state should be set to high (MSTR = 1,
CPOL = 1 and CPHA = 1 for the MC68HC11 family).
Figure 5 shows the recommended configuration and
directon of data flow. Note that an additional I/O line is
Figure 4. Internal MAIN and SUB Panel LED Disable Circuit
ENABLE
U
I
U
LED
+
–
~1V
–
U
+
3205 F04
MAIN1-MAIN4
SUB1, SUB2
10 A
CPO
W
U
Table 3. RGB Duty Cycles
total of 4096 colors. Table 3 indicates the decoding of the
red, green and blue LEDs.
The full-scale currents in the red, green and blue LEDs are
controlled by the current at the I
to those in the main and sub panels. The I
regulated at 1.223V and the LED current is a precise
multiple of the I
The RGB display LED currents will follow the relationship:
where R
I
RED GREENBLUE
D11
D7
D3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
,
RGB
is the value of the resistor on the I
,
Figure 5. Microcontroller Interface
D10
CONTROLLER
D6
D2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
RGB
MOSI
GPIO
current.
SCK
400
D9
D5
D1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
1 223
R
.
RGB
RGB
V
D8
D4
D0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
D
SCLK
LD
pin in a similar manner
IN
LTC3205
LTC3205
CODE
HEX
A
B
C
D
0
1
2
3
4
5
6
7
8
9
E
F
3205 F05
RGB
CYCLE (%)
RGB
DUTY
10/15
11/15
12/15
13/15
14/15
15/15
0/15
1/15
2/15
3/15
4/15
5/15
6/15
7/15
8/15
9/15
pin is
pin.
9
3205f