TLC59116_1 Datasheet, PDF (17/30 Pages) Texas Instruments – 16-CHANNEL Fm+ I2C-BUS CONSTANT-CURRENT LED SINK DRIVER

TLC59116
www.ti.com .................................................................................................................................................... SLDS157B – FEBRUARY 2008 – REVISED JULY 2008
Output Gain Control Register (IREF)
Table 11 describes the Output Gain Control Register.
ADDRESS
1Ch
Table 11. IREF – Output Gain Control Register (Address 1Ch) Bit Description
REGISTER
IREF
BIT
SYMBOL ACCESS⁽¹⁾
VALUE
DESCRIPTION
7
CM
R/W
1 ⁽²⁾
High/low current multiplier
6
HC
R/W
1 ⁽²⁾
Subcurrent
5:0
CC[5:0]
R/W
11 1111⁽²⁾ Current multiplier
(1) R = read, W = write
(2) Default value
IREF determines the voltage gain (VG), which affects the voltage at the REXT terminal and indirectly the
reference current (I_ref) flowing through the external resistor at terminal REXT. Bit 0 is the Current Multiplier (CM)
bit, which determines the ratio I_OUT,target/I_ref. Each combination of VG and CM sets a Current Gain (CG).
• VG: the relationship between {HC,CC[0:5]} and the voltage gain is calculated as shown:
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 subband (HC = 0): VG = 1/4 to 127/256, linearly divided into 64 steps
High-voltage subband (HC = 1): VG = 1/2 to 127/128, linearly divided into 64 steps
• CM: In addition to determining the ratio I_OUT,target/I_ref, CM limits the output current range.
High Current Multiplier (CM = 1): I_OUT,target/I_ref = 15, suitable for output current range I_OUT = 10 mA to 120 mA.
Low Current Multiplier (CM = 0): I_OUT,target/I_ref = 5, suitable for output current range I_OUT = 5 mA to 40 mA
• CG: The total Current Gain is defined as:
V_REXT = 1.26 V × VG
I_ref = V_REXT/R_ext, if the external resistor (R_ext) is connected to ground.
I_OUT,target = I_ref × 15 × 3^{CM – 1} = 1.26 V/R_ext × VG × 15 × 3^{CM – 1} = (1.26 V/R_ext × 15) × CG
CG = VG × 3^{CM – 1}
Therefore, CG = (1/12) to (127/128), divided into 256 steps.
Examples
• IREF Code {CM, HC, CC[0:5]} = {1,1,111111}
VG = 127/128 = 0.992 and CG = VG × 3⁰ = VG = 0.992
• IREF Code {CM, HC, CC[0:5]} = {1,1,000000}
VG = (1 + 1) × (1 + 0/64)/4 = 1/2 = 0.5, and CG = 0.5
• IREF Code {CM, HC, CC[0:5]} = {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 9.
Copyright © 2008, Texas Instruments Incorporated
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