TLC5916IPWR datasheet(22/30 Pages) TI

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8-Bit Configuration Code and Current Gain

TLC5916, TLC5917

8-BIT CONSTANT-CURRENT LED SINK DRIVERS

SLVS695A – JUNE 2007 – REVISED MARCH 2008

Bit definition of the Configuration Code in the Configuration Latch is shown in Table 4.

Table 4. Bit Definition of 8-Bit Configuration Code

Bit 0

Bit 1

Bit 2

Bit 3

Bit 4

Bit 5

Bit 6

Bit 7

Meaning

CC0

CC1

CC2

CC3

CC4

CC5

Default

Bit 7 is first sent into TLC5916/TLC5917 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)

× (1 + D/64) / 4

D = CC0

× 25 + CC1 × 24 + CC2 × 23 + CC3 × 22 + CC4 × 21 + CC5 × 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 I

OUT,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 × VG

Iref = VR-EXT/Rext, if the external resistor, Rext, is connected to ground.

IOUT,target = Iref × 15 × 3

CM – 1 = 1.26 V/R

ext × VG × 15 × 3

CM – 1 = (1.26 V/R

ext × 15) × CG

CG = VG

× 3CM – 1

Therefore, CG = (1/12) to (127/128), and it is divided into 256 steps. If CG = 127/128 = 0.992, the

IOUT,target-Rext.

Examples

• Configuration Code {CM, HC, CC[0:5]} = {1,1,111111}

VG = 127/128 = 0.992 and CG = VG

× 30 = VG = 0.992

• Configuration Code = {1,1,000000}

VG = (1 + 1)

× (1 + 0/64)/4 = 1/2 = 0.5, and CG = 0.5

• Configuration Code = {0,0,000000}

VG = (1 + 0)

× (1 + 0/64)/4 = 1/4, and CG = (1/4) × 3–1 = 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 19.

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