LTC3206 Datasheet, PDF (11/16 Pages) Linear Technology – I2C Multidisplay LED Controller

LTC3206
APPLICATIO S I FOR ATIO
The RED, GREEN and BLUE pins can also enable the
charge pump, however, since they each have individual
disable control they can be left floating or grounded if
unused.
RGB Illuminator Brightness Control
The RED, GREEN and BLUE LEDs can be individually set
to have a linear 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 total of 4096 colors. Table 1 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, SUB and AUX LEDs. The
I_RGB pin also servos to 0.6V and the RGB LED currents are
a precise multiple of the I_RGB current. The DC value of the
RGB display LED currents will follow the relationship:
I_{RED,GREEN,BLUE}
=
400
0.6V
R_RGB
where R_RGB is the value of the resistor at the I_RGB pin.
The average value of the current in the RED, GREEN and
BLUE LEDs will be:
AVG
(I_{RED,GREEN,BLUE})
=
400
•
D
15
•
0.6V
R_RGB
where D is the decimal equivalent of the 4-bit digital code
programmed for the given LED(0 to 15). Table 1 summa-
rizes the RED, GREEN and BLUE LED power settings.
The RED, GREEN and BLUE LEDs are pulse width modu-
lated at a frequency of 1/240 of the frequency of the charge
pump oscillator or about 4kHz.
ENRGB/S Pin
The ENRGB/S pin can be used to enable or disable the
LTC3206 without re-accessing the I²C port. This might be
useful to indicate an incoming phone call without waking
the microcontroller. ENRGB/S can be software pro-
grammed as an independent control for either the RGB
display or the SUB display. Control bit A2 in the serial port
(see Figure 3 and Table 3) determines which display
ENRGB/S controls. When bit A2 is 0, the ENRGB/S pin
controls the RGB display. If it is set to 1, ENRGB/S controls
the SUB display.
To use the ENRGB/S pin, the I²C port must first be
configured to the desired setting. For example, if ENRGB/S
will be used to control the SUB display, then a non-zero
code must reside in the C3-C0 nibble of the I²C port and bit
A2 must be set to 1 (see Table 1). Now when ENRGB/S is
high (DV_CC), the SUB display will be on with the C3-C0
setting. When ENRGB/S is low, the SUB display will be off.
If no other displays are programmed to be on, the entire
chip will be in shutdown.
Likewise, if ENRGB/S will be used to enable the RGB
display, then a non-zero code must reside in one of the
RED, GREEN or BLUE nibbles of the serial port (A4-A7 or
B0-B7), and bit A2 must be 0. Now when ENRGB/S is high
(DV_CC), the RGB display will light with the programmed
color. When ENRGB/S is low, the RGB display will be off.
If no other displays are programmed to be on, the entire
chip will be in shutdown.
If bit A2 is set to 1 (SUB display control), then ENRGB/S
will have no effect on the RGB display. Likewise, if bit A2
is set to 0 (RGB display control), then ENRGB/S will have
no effect on the SUB display.
If the ENRGB/S pin is not used, it should be connected to
DV_CC. It should not be grounded or left floating.
V_IN, CPO Capacitor Selection
The style and value of capacitors used with the LTC3206
determine several important parameters such as regulator
control-loop stability, output ripple and charge pump
strength. To reduce noise and ripple, it is recommended
that low equivalent series resistance (ESR) multilayer
ceramic capacitors be used on both V_IN and CPO. Tanta-
lum and aluminum capacitors are not recommended be-
cause of their high ESR. The value of the capacitor on CPO
directly controls the amount of output ripple for a given
load current. Increasing the size of this capacitor will
reduce the output ripple. The peak-to-peak output ripple is
approximately given by the expression:
V_RIPPLEP-P
≅
I_CPO
3f_OSC • C_CPO
3206f
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