LTC3205_15 Datasheet, PDF(8/16 Page) Linear Technology

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LTC3205_15 Datasheet, PDF (8/16 Pages) Linear Technology – Multidisplay LED Controller

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LTC3205

OPERATIO

LTC3205 is in shutdown when DVCC is grounded. Note,

however, that all of the logic signals that are referenced to

DVCC (DIN, SCLK, LD, ENRGB and STEPUP) will need to be

at DVCC or below (i.e., ground) to keep from violating the

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 DIN input is loaded on the rising edge of SCLK. D15 is

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.

tLC tDS tDH

The current levels of both the main and sub displays are

controlled by precisely mirroring a multiple of the current

at the IMS pin.

The main and sub display LED currents will follow the

relationship:

IMAIN/SUB

N 1.223V

RMAIN/SUB

where N is equal to 400, 200, 100 or 0 depending on which

current setting is selected. RMAIN/SUB is the value of the

resistor on the IMS pin. The scale factors are spaced pseudo

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.

Table 2. Main and Sub Display Current Levels

FRACTION OF

D15

D14

FULL-SCALE

D13

D12

CURRENT (%)

100

tCL

tLW

SCLK

DIN

D15

D14

3205 F03

Figure 3. Serial Port Timing Diagram

Table 1. Serial Port Mapping

D15 D14 D13 D12 D11 D10 D9 D8

MAIN1-

MAIN4

Current

Level

(Table 2)

SUB1-

SUB2

Current

Level

(Table 2)

Blue LED Duty Cycle

(Table 3)

D7 D6 D5 D4

Green LED Duty Cycle

(Table 3)

D3 D2 D1 D0

Red LED Duty Cycle

(Table 3)

3205f

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