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AN3981 Datasheet(PDF) 35 Page - STMicroelectronics

Part # AN3981
Description  LED array drivers
PDF  54 Pages
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Manufacturer  STMICROELECTRONICS [STMicroelectronics]
Direct Link  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

AN3981 Datasheet(HTML) 35 Page - STMicroelectronics

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AN3981
Common application information
Doc ID 022217 Rev 1
35/54
Moreover the extra voltage across the red LEDs driving generators may cause an erroneous
shorted LED condition detection.
To avoid these drawbacks, two different approaches are possible:
1.
Figure 41 shows an application with only one voltage rail (VLED). A resistor in series to
each red LED is added. In this way, the voltage excess drops across the resistor
instead of dropping across the current generators. This solution implies a significant
reduction of the power dissipated by the chip. However the total power dissipation does
not change and a large part of the power is still wasted on the series resistor.
This not only affects the efficiency, but also raises the cost of the system due to the need to
dissipate the generated heat.
Figure 41.
Solution with single supply voltage
2.
Figure 42 shows a solution with two separate voltage rails: one for blue and green
LEDs (VLED) and one for red LEDs (VLED_RED), which can be derived from the
former (e.g. simply using a switching regulator).
This solution is by far the most advantageous in terms of power dissipation. Voltage rails are
tailored to the type of LEDs they drive and the wasted power is significantly reduced as well
as the heat produced.
AM10641v1
STP1612PW05
OUT0
OUT15
V
O,red
V
F,red
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
OUT0
OUT15
V
O,red
V
F,red
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
OUT0
OUT15
V
O,red
V
F,red
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
OUT0
OUT15
V
O,red
V
F,red
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
to SDI of
the next
device
from SDO of
the previous
device
to SDI of
the next
device
from SDO of
the previous
device
to SDI of
the next
device
from SDO of
the previous
device
SDO
SDI
SDO
SDI
SDO
SDI
VLED = 5V
VLED_RED = 3.3V
V
O,green
V
O,blue
V
O,red
VLED
V
F,green
V
F,blue
V
F,red
VLED_RED
voltage
regulator
VLED_RED
3.3V
VLED
5V
STPxx..yy05
STPxx..yy05
STPxx..yy05
STPxx..yy05
STPxx..yy05
STPxx..yy05
STP1612PW05
OUT0
OUT15
V
O,red
V
F,red
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
OUT0
OUT15
V
O,red
V
F,red
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
OUT0
OUT15
V
O,red
V
F,red
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
OUT0
OUT15
V
O,red
V
F,red
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,green
V
F,green
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
STP1612PW05
V
O,blue
V
F,blue
OUT0
OUT15
……
to SDI of
the next
device
from SDO of
the previous
device
to SDI of
the next
device
from SDO of
the previous
device
to SDI of
the next
device
from SDO of
the previous
device
SDO
SDI
SDO
SDI
SDO
SDI
VLED = 5V
VLED_RED = 3.3V
V
O,green
V
O,blue
V
O,red
VLED
V
F,green
V
F,blue
V
F,red
VLED_RED
V
O,green
V
O,blue
V
O,red
VLED
V
F,green
V
F,blue
V
F,red
VLED_RED
voltage
regulator
VLED_RED
3.3V
VLED
5V
STPxx..yy05
STPxx..yy05
STPxx..yy05
STPxx..yy05
STPxx..yy05
STPxx..yy05



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