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TLC5926 Datasheet, PDF (19/29 Pages) Texas Instruments – 16-CHANNEL CONSTANT-CURRENT LED SINK DRIVERS | |||
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TLC5926, TLC5927
www.ti.com ....................................................................................................................................................................................................... SLVS677 â JULY 2008
Table 3. Overtemperature Detection(1)
STATE OF OUTPUT PORT
Off
On
On â all channels
Off
On
On â Off
CONDITION
IOUT = 0 mA
Tj < Tj,trip global
Tj > Tj,trip global
Tj < Tj,trip channel n
Tj > Tj,trip channel n
ERROR STATUS CODE
0
1
All error status bits = 0
1
Channel n error status bit = 0
(1) The global shutdown threshold temperature is approximately 170°C.
MEANING
Normal
Global overtemperature
Normal
Channel n overtemperature
16-Bit Configuration Code and Current Gain
Bit definition of the Configuration Code in the Configuration Latch is shown in Table 4.
Meaning
Default
Bit 0
CM
1
Table 4. Bit Definition of 8-Bit Configuration Code
Bit 1
HC
1
Bit 2
CC0
1
Bit 3
CC1
1
Bit 4
CC2
1
Bit 5
CC3
1
Bit 6
CC4
1
Bit 7
CC5
1
Bit 8â15
Don't care
X
Bit 7 is first sent into TLC5926/TLC5927 via SDI. Bits 1 to 7 {HC, CC[0:5]} determine the voltage gain (VG) that
affects the voltage at R-EXT and indirectly affects the reference current, Iref, flowing through the external resistor
at R-EXT. Bit 0 is the Current Multiplier (CM) that determines the ratio IOUT,target/Iref. Each combination of VG and
CM gives a specific Current Gain (CG).
⢠VG: the relationship between {HC,CC[0:5]} and the voltage gain is calculated as shown below:
VG = (1 + HC) Ã (1 + D/64) / 4
D = CC0 Ã 25 + CC1 Ã 24 + CC2 Ã 23 + CC3 Ã 22 + CC4 Ã 21 + CC5 Ã 20
Where HC is 1 or 0, and D is the binary value of CC[0:5]. So, the VG could be regarded as a floating-point
number with 1-bit exponent HC and 6-bit mantissa CC[0:5]. {HC,CC[0:5]} divides the programmable voltage
gain VG into 128 steps and two sub-bands:
Low voltage sub-band (HC = 0): VG = 1/4 ~ 127/256, linearly divided into 64 steps
High voltage sub-band (HC = 1): VG = 1/2 ~ 127/128, linearly divided into 64 steps
⢠CM: In addition to determining the ratio IOUT,target/Iref, CM limits the output current range.
High Current Multiplier (CM = 1): IOUT,target/Iref = 15, suitable for output current range IOUT = 10 mA to 120 mA.
Low Current Multiplier (CM = 0): IOUT,target/Iref = 5, suitable for output current range IOUT = 5 mA to 40 mA
⢠CG: The total Current Gain is defined as the following.
VR-EXT = 1.26 V Ã VG
Iref = VR-EXT/Rext, if the external resistor, Rext, is connected to ground.
IOUT,target = Iref à 15 à 3CM â 1 = 1.26 V/Rext à VG à 15 à 3CM â 1 = (1.26 V/Rext à 15) à CG
CG = VG Ã 3CM â 1
Therefore, CG = (1/12) to (127/128) divided into 256 steps.
Examples
⢠Configuration Code {CM, HC, CC[0:5]} = {1,1,111111}
VG = 127/128 = 0.992 and CG = VG Ã 30 = VG = 0.992
⢠Configuration Code = {1,1,000000}
VG = (1 + 1) Ã (1 + 0/64)/4 = 1/2 = 0.5, and CG = 0.5
⢠Configuration Code = {0,0,000000}
VG = (1 + 0) Ã (1 + 0/64)/4 = 1/4, and CG = (1/4) Ã 3â1 = 1/12
After power on, the default value of the Configuration Code {CM, HC, CC[0:5]} is {1,1,111111}. Therefore,
VG = CG = 0.992. The relationship between the Configuration Code and the Current Gain is shown in Figure 15.
Copyright © 2008, Texas Instruments Incorporated
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Product Folder Link(s): TLC5926 TLC5927
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