LTC3205EUF Linear Technology, LTC3205EUF Datasheet - Page 8

• 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
LTC3205
LTC3205 is in shutdown when DV
however, that all of the logic signals that are referenced to
DV
at DV
absolute maximum specifications on these pins.
Serial Port
The microcontroller compatible serial port provides all of
the command and control inputs for the LTC3205. Data on
the D
loaded first and D0 last. Once all bits have been clocked into
the shift register, the command data is loaded into the
command register by bringing LD low. At this time, the
command register is latched and the LTC3205 will begin
to act upon the new command set. The serial port uses static
logic registers so there is no minimum speed at which it can
be operated. Figure 3 shows the operation of the serial port.
Table 1 shows the mapping of the serial port bits to the
operation of the various displays. Bits D15 and D14
control the brightness of the four LEDs in the main display.
Bits D13 and D12 control the brightness of the two LEDs
in the sub display. The red, green and blue LEDs each have
four bits assigned giving a linear range of 16 brightness
levels to each of the LEDs.
Programming the MAIN and SUB LED Currents
Table 2 indicates the decoding of the Main and Sub display
control bits.
8
CC
IN
CC
(D
input is loaded on the rising edge of SCLK. D15 is
IN
or below (i.e., ground) to keep from violating the
Table 1. Serial Port Mapping
, SCLK, LD, ENRGB and STEPUP) will need to be
D15
(Table 2)
MAIN1-
Current
MAIN4
Level
D14
U
SCLK
D13
D
LD
IN
(Table 2)
Current
SUB1-
SUB2
Level
D12
t
X
LC
t
DS
D11
CC
D15
Blue LED Duty Cycle
t
is grounded. Note,
DH
D10
(Table 3)
Figure 3. Serial Port Timing Diagram
D14
D9
D8
D7
D2
The current levels of both the main and sub displays are
controlled by precisely mirroring a multiple of the current
at the I
The main and sub display LED currents will follow the
relationship:
where N is equal to 400, 200, 100 or 0 depending on which
current setting is selected. R
resistor on the I
exponentially to compensate for the vision perception of
the human eye (zero is a special case needed for
shutdown).
The LTC3205 can power up to six white LEDs (four for the
main display, two for the sub display), however, it is not
necessary to have all six in each application. Any of the four
main or two sub LED outputs can be disabled by connect-
ing the unused output to CPO.
Green LED Duty Cycle
t
H
I
MAIN SUB
D6
(Table 3)
MS
D1
Table 2. Main and Sub Display Current Levels
/
pin.
D5
D15
D13
0
0
1
1
t
MS
L
N
D0
R
D4
pin. The scale factors are spaced pseudo
MAIN SUB
. 1 223
t
CL
X
/
D14
D12
D3
0
1
0
1
V
Red LED Duty Cycle
t
LW
MAIN/SUB
D2
(Table 3)
3205 F03
CURRENT (%)
FRACTION OF
FULL-SCALE
D1
is the value of the
100
25
50
0
D0
3205f