LTC3205_15 Datasheet, PDF (9/16 Pages) Linear Technology – Multidisplay LED Controller

U
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 10µA 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.
CPO
~1V
–+
MAIN1-MAIN4
SUB1, SUB2
ENABLE
I_LED
10µA
3205 F04
Figure 4. Internal MAIN and SUB Panel LED Disable Circuit
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
LTC3205
Table 3. RGB Duty Cycles
D11
D10
D9
D7
D6
D5
D3
D2
D1
0
0
0
0
0
0
0
0
1
0
0
1
0
1
0
0
1
0
0
1
1
0
1
1
1
0
0
1
0
0
1
0
1
1
0
1
1
1
0
1
1
0
1
1
1
1
1
1
D8
D4
HEX
DUTY
D0 CODE CYCLE (%)
0
0
0/15
1
1
1/15
0
2
2/15
1
3
3/15
0
4
4/15
1
5
5/15
0
6
6/15
1
7
7/15
0
8
8/15
1
9
9/15
0
A
10/15
1
B
11/15
0
C
12/15
1
D
13/15
0
E
14/15
1
F
15/15
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_RGB pin in a similar manner
to those in the main and sub panels. The I_RGB pin is
regulated at 1.223V and the LED current is a precise
multiple of the I_RGB current.
The RGB display LED currents will follow the relationship:
I_{RED,GREEN,BLUE}
=
400
1.223V
R_RGB
where R_RGB is the value of the resistor on the I_RGB pin.
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
µCONTROLLER
MOSI
SCK
GPIO
LTC3205
D_IN
SCLK
LD
3205 F05
Figure 5. Microcontroller Interface
3205f
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