SBVS237 March   2014 TLC5955

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Terminal Configurations and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Handling Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
    1. 7.1 Terminal-Equivalent Input and Output Schematic Diagrams
    2. 7.2 Test Circuits
    3. 7.3 Timing Diagrams
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Output Current Calculation
      2. 8.3.2 Register and Data Latch Configuration
        1. 8.3.2.1 769-Bit Common Shift Register
        2. 8.3.2.2 Grayscale (GS) Data Latch
        3. 8.3.2.3 Control Data Latch
        4. 8.3.2.4 Dot Correction (DC) Data Latch
        5. 8.3.2.5 Maximum Current (MC) Data Latch
        6. 8.3.2.6 Global Brightness Control (BC) Data Latch
        7. 8.3.2.7 Function Control (FC) Data Latch
      3. 8.3.3 Status Information Data (SID)
      4. 8.3.4 LED Open Detection (LOD)
      5. 8.3.5 LED Short Detection (LSD)
      6. 8.3.6 Noise Reduction
    4. 8.4 Device Functional Modes
      1. 8.4.1 Maximum Current Control (MC) Function
      2. 8.4.2 Dot Correction (DC) Function
      3. 8.4.3 Global Brightness Control (BC) Function
      4. 8.4.4 Grayscale (GS) Function (PWM Control)
        1. 8.4.4.1 Conventional PWM Control
        2. 8.4.4.2 Enhanced Spectrum (ES) PWM Control
        3. 8.4.4.3 Auto Display Repeat Function
        4. 8.4.4.4 Display Timing Reset Function
        5. 8.4.4.5 Auto Data Refresh Function
  9. 9 Applications and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Daisy-Chain Application
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Step-by-Step Design Procedure
          2. 9.2.1.2.2 Maximum Current (MC) Data
          3. 9.2.1.2.3 Global Brightness Control (BC) Data
          4. 9.2.1.2.4 Dot Correction (DC) Data
          5. 9.2.1.2.5 Grayscale (GS) Data
          6. 9.2.1.2.6 Other Control Data
        3. 9.2.1.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8 Detailed Description

8.1 Overview

The TLC5955 is 48-channel, 30-mA, constant-current LED driver that can control LED on-time with pulse width modulation (PWM) in 65,536 steps for grayscale (GS) control. A maximum of 281 trillion colors can be generated with red, green, and blue LEDs connected to the constant-current outputs.

The device has a 128-step, 7-bit, output current control function called dot correction (DC) that can control each constant-current output. Inherently, LED lamps have different intensities resulting from manufacturing differences. The DC function can reduce the inherent differences in intensity and improve LED lamp brightness uniformity.

The device also has a 128-step, 7-bit, output current control function called global brightness control (BC) that can control each color group output. The BC function can adjust the red, green, and blue LED intensity for true white with constant-current control. The device contributes higher image quality to LED displays with fine white balance tuning by using these GS, DC, and BC functions.

The display controller can locate LED lamp failures via the device because the controller can detect LED lamp failures with the LED open detection (LOD) and LED short detection (LSD) functions and the reliability of the display can be improved by the LOD, LSD function.

The device maximum constant-current output value can be set by internal register data instead of the general method of using an external resistor setting. Thus, any failure modes that occur from the external resistor can be eliminated and one resistor can be eliminated.

The device constant-current output can drive approximately 19 mA at a 0.25-V output voltage and a +25°C ambient temperature. This voltage is called knee voltage. This 0.25-V, low-knee voltage can contribute to the design of a lower-power display system. The total number of LED drivers on one LED display panel can be reduced because 48 LED lamps can be driven by one LED driver. Therefore, designing fine-pitch LED displays is simplified.

8.2 Functional Block Diagram

fbd_sbvs237.gif

8.3 Feature Description

8.3.1 Output Current Calculation

The output current value controlled by MC, DC, and BC can be calculated by Equation 1.

Equation 1. q_iolcn_bvs237.gif

where:

  • IOLCMax = the maximum constant-current value for all OUTXn for each color group programmed by MC data,
  • DCXn = the dot correction value for each channel (0h to 7Fh),
  • BCX = the global brightness control value (0h to 7Fh),
  • X = R, G, or B for the red, green, or blue color group, and
  • n = 0 to 15.

    • Each output sinks the IOLCMax current when they turn on and the dot correction (DC) data and the global brightness control (BC) data are set to the maximum value of 7Fh (127d). Each output sink current can be reduced by lowering the DC and BC values.

    When IOUT is set lower than 1 mA by both MC and BC or BC only, the output may be unstable. Output currents lower than 1 mA can be achieved by setting IOUT to 1 mA with MC and BC or BC only and then using DC to lower the output current.

    8.3.2 Register and Data Latch Configuration

    The TLC5955 has one common shift register and three data latches: the grayscale (GS) data latch, the control data latch, and the dot correction (DC) data latch. The common shift register is 769 bits long, the GS data latch is 768 bits long, the control data latch is 371 bits long, and the DC data latch is 336 bits long.

    If the common shift register MSB is 0, the least significant 768 bits from the common shift register are latched into the GS data latch. If the MSB is 1, and bits 767 to 760 are 96h (10010110b), the data are latched into the control data latch. Refer to Figure 21 for the common shift register, GS data latch, control data latch, and DC data latch configurations.

    fc_comm_shift_reg_sbvs237.gifFigure 21. Common Shift Register and Data Latches Configuration

    8.3.2.1 769-Bit Common Shift Register

    The 769-bit common shift register is used to shift data from the SIN terminal into the TLC5955. The data shifted into the register are used for GS, DC, maximum output current, global BC functions, and function control data write operations. The common shift register LSB is connected to SIN and the MSB is connected to SOUT. On each SCLK rising edge, the data on SIN are shifted into the LSB and all 769 bits are shifted towards the MSB. The register MSB is always connected to SOUT. When the device is powered up, the data in the 769-bit common shift register are random.

    8.3.2.2 Grayscale (GS) Data Latch

    The GS data latch is 768 bits long, and sets the PWM timing for each constant-current output. The on-time of all constant-current outputs is controlled by the data in this data latch. The 768-bit GS data in the common shift register are copied to the data latch at a LAT rising edge when the common shift resister MSB is 0.

    When the device is powered up, the data are random and all constant-current outputs are forced off. However, no outputs turn on until GS data are written to the GS data latch even if a GSCLK is input. The data bit assignment is shown in Table 1. Refer to Figure 22 for a GS data write timing diagram.

    Table 1. Grayscale Data Latch Bit Description

    GS DATA LATCH BIT NUMBER BIT NAME DEFAULT VALUE CONTROLLED CHANNEL GS DATA LATCH BIT NUMBER BIT NAME DEFAULT VALUE CONTROLLED CHANNEL
    15-0 GSR0[15:0] N/A
    (no default value)    		 Bits[15:0] for OUTR0 399-384 GSR8[15:0] N/A
    (no default value)    		 Bits[15:0] for OUTR8
    31-16 GSG0[15:0] Bits[15:0] for OUTG0 415-400 GSG8[15:0] Bits[15:0] for OUTG8
    47-32 GSB0[15:0] Bits[15:0] for OUTB0 431-416 GSB8[15:0] Bits[15:0] for OUTB8
    63-48 GSR1[15:0] Bits[15:0] for OUTR1 447-432 GSR9[15:0] Bits[15:0] for OUTR9
    79-64 GSG1[15:0] Bits[15:0] for OUTG1 463-448 GSG9[15:0] Bits[15:0] for OUTG9
    95-80 GSB1[15:0] Bits[15:0] for OUTB1 479-464 GSB9[15:0] Bits[15:0] for OUTB9
    111-96 GSR2[15:0] Bits[15:0] for OUTR2 495-480 GSR10[15:0] Bits[15:0] for OUTR10
    127-112 GSG2[15:0] Bits[15:0] for OUTG2 511-496 GSG10[15:0] Bits[15:0] for OUTG10
    143-128 GSB2[15:0] Bits[15:0] for OUTB2 527-512 GSB10[15:0] Bits[15:0] for OUTB10
    159-144 GSR3[15:0] Bits[15:0] for OUTR3 543-528 GSR11[15:0] Bits[15:0] for OUTR11
    175-160 GSG3[15:0] Bits[15:0] for OUTG3 559-544 GSG11[15:0] Bits[15:0] for OUTG11
    191-176 GSB3[15:0] Bits[15:0] for OUTB3 575-560 GSB11[15:0] Bits[15:0] for OUTB11
    207-192 GSR4[15:0] Bits[15:0] for OUTR4 591-576 GSR12[15:0] Bits[15:0] for OUTR12
    223-208 GSG4[15:0] Bits[15:0] for OUTG4 607-592 GSG12[15:0] Bits[15:0] for OUTG12
    239-224 GSB4[15:0] Bits[15:0] for OUTB4 623-608 GSB12[15:0] Bits[15:0] for OUTB12
    255-240 GSR5[15:0] Bits[15:0] for OUTR5 639-624 GSR13[15:0] Bits[15:0] for OUTR13
    271-256 GSG5[15:0] Bits[15:0] for OUTG5 655-640 GSG13[15:0] Bits[15:0] for OUTG13
    287-272 GSB5[15:0] Bits[15:0] for OUTB5 671-656 GSB13[15:0] Bits[15:0] for OUTB13
    303-288 GSR6[15:0] Bits[15:0] for OUTR6 687-672 GSR14[15:0] Bits[15:0] for OUTR14
    319-304 GSG6[15:0] Bits[15:0] for OUTG6 703-688 GSG14[15:0] Bits[15:0] for OUTG14
    335-320 GSB6[15:0] Bits[15:0] for OUTB6 719-704 GSB14[15:0] Bits[15:0] for OUTB14
    351-336 GSR7[15:0] Bits[15:0] for OUTR7 735-720 GSR15[15:0] Bits[15:0] for OUTR15
    367-352 GSG7[15:0] Bits[15:0] for OUTG7 751-736 GSG15[15:0] Bits[15:0] for OUTG15
    383-368 GSB7[15:0] Bits[15:0] for OUTB7 767-752 GSB15[15:0] Bits[15:0] for OUTB15
    td_GS_data_write_sbvs237.gifFigure 22. Grayscale Data Write Timing Diagram (RFRESH = 0)

    8.3.2.3 Control Data Latch

    The control data latch is 371 bits long. The data latch contains dot correction (DC) data, maximum current (MC) data, global brightness control (BC) data, and function control (FC) data. The DC for each constant-current output are controlled by the data in the DC data latch. The control data in the data latch are updated with the lower 371 bits of the common shift register at the LAT rising edge when the common shift register MSB is 1. The 336 bits of DC data are copied from the control data latch when the 65,536th GSCLK is input with RFRESH set to 1 in the control data latch after the GS data are written or the LAT rising edge for GS data writes is input when the RFRESH bit is 0.

    When the device is powered up, the data in the control data latch (except the MC bits) are random. Therefore, DC, BC, and FC data must be written to the control data latch before turning on the constant-current outputs. Furthermore, MC data should be set appropriately for the application. Refer to Figure 23 for a control data write timing diagram.

    td_ctrl_data_write_sbvs237.gifFigure 23. Control Data Write Timing Diagram for DC, MC, BC, and FC

    8.3.2.4 Dot Correction (DC) Data Latch

    DC data are 336 bits long; the data for each constant-current output are controlled by seven bits. Each constant-current output DC is controlled by the DC data latch. Each DC value individually adjusts the output current for each constant-current output. As explained in the Dot Correction (DC) Function section, the DC values are used to adjust the output current from 26.2% to 100% of the current value set by MC and BC data. When the device is powered on, the data in the DC data latch are random.

    The DC data bit assignment is shown in Table 2. See Table 9 for a summary of the DC data value versus set current value.

    Table 2. Dot Correction Data Bit Description

    CONTROL DATA LATCH BIT NUMBER BIT NAME DEFAULT VALUE CONTROLLED CHANNEL CONTROL DATA LATCH BIT NUMBER BIT NAME DEFAULT VALUE CONTROLLED CHANNEL
    6-0 DCR0[6:0] N/A
    (no default value)    		 DC bits[6:0] for OUTR0 174-168 DCR8[6:0] N/A
    (no default value)    		 DC bits[6:0] for OUTR8
    13-7 DCG0[6:0] DC bits[6:0] for OUTG0 181-175 DCG8[6:0] DC bits[6:0] for OUTG8
    20-14 DCB0[6:0] DC bits[6:0] for OUTB0 188-182 DCB8[6:0] DC bits[6:0] for OUTB8
    27-21 DCR1[6:0] DC bits[6:0] for OUTR1 195-189 DCR9[6:0] DC bits[6:0] for OUTR9
    34-28 DCG1[6:0] DC bits[6:0] for OUTG1 202-196 DCG9[6:0] DC bits[6:0] for OUTG9
    41-35 DCB1[6:0] DC bits[6:0] for OUTB1 209-203 DCB9[6:0] DC bits[6:0] for OUTB9
    48-42 DCR2[6:0] DC bits[6:0] for OUTR2 216-210 DCR10[6:0] DC bits[6:0] for OUTR10
    55-49 DCG2[6:0] DC bits[6:0] for OUTG2 223-217 DCG10[6:0] DC bits[6:0] for OUTG10
    62-56 DCB2[6:0] DC bits[6:0] for OUTB2 230-224 DCB10[6:0] DC bits[6:0] for OUTB10
    69-63 DCR3[6:0] DC bits[6:0] for OUTR3 237-231 DCR11[6:0] DC bits[6:0] for OUTR11
    76-70 DCG3[6:0] DC bits[6:0] for OUTG3 244-238 DCG11[6:0] DC bits[6:0] for OUTG11
    83-77 DCB3[6:0] DC bits[6:0] for OUTB3 251-245 DCB11[6:0] DC bits[6:0] for OUTB11
    90-84 DCR4[6:0] DC bits[6:0] for OUTR4 258-252 DCR12[6:0] DC bits[6:0] for OUTR12
    97-91 DCG4[6:0] DC bits[6:0] for OUTG4 265-259 DCG12[6:0] DC bits[6:0] for OUTG12
    104-98 DCB4[6:0] DC bits[6:0] for OUTB4 272-266 DCB12[6:0] DC bits[6:0] for OUTB12
    111-105 DCR5[6:0] DC bits[6:0] for OUTR5 279-273 DCR13[6:0] DC bits[6:0] for OUTR13
    118-112 DCG5[6:0] DC bits[6:0] for OUTG5 286-280 DCG13[6:0] DC bits[6:0] for OUTG13
    125-119 DCB5[6:0] DC bits[6:0] for OUTB5 293-287 DCB13[6:0] DC bits[6:0] for OUTB13
    132-126 DCR6[6:0] DC bits[6:0] for OUTR6 300-294 DCR14[6:0] DC bits[6:0] for OUTR14
    139-133 DCG6[6:0] DC bits[6:0] for OUTG6 307-301 DCG14[6:0] DC bits[6:0] for OUTG14
    146-140 DCB6[6:0] DC bits[6:0] for OUTB6 314-308 DCB14[6:0] DC bits[6:0] for OUTB14
    153-147 DCR7[6:0] DC bits[6:0] for OUTR7 321-315 DCR15[6:0] DC bits[6:0] for OUTR15
    160-154 DCG7[6:0] DC bits[6:0] for OUTG7 328-322 DCG15[6:0] DC bits[6:0] for OUTG15
    167-161 DCB7[6:0] DC bits[6:0] for OUTB7 335-329 DCB15[6:0] DC bits[6:0] for OUTB15

    8.3.2.5 Maximum Current (MC) Data Latch

    The maximum output current per channel, IOLCMax, is programmed by MC data and can be set with the serial interface. IOLCMax is the largest current for each output. Each output sinks the IOLCMax current when they turn on with DC and BC data set to the maximum value of 7Fh (127d). MC data must have the same data continuously written twice in order to change the data. When the device is powered on, the MC data are set to 0.

    The MC data bit assignment is shown in Table 3. See Table 8 for a summary of the MC data value for each color group versus the set current value.

    Table 3. Maximum Current Data Bit Assignment in the Control Data Latch

    CONTROL DATA LATCH BIT NUMBER BIT NAME DEFAULT VALUE CONTROLLED CHANNEL
    338-336 MCR[2:0] 0 MC bits[2:0] for red color group channels (OUTR0 to OUTR15)
    341-339 MCG[2:0] 0 MC bits[2:0] for green color group channels (OUTG0 to OUTG15)
    344-342 MCB[2:0] 0 MC bits[2:0] for blue color group channels (OUTB0 to OUTB15)

    8.3.2.6 Global Brightness Control (BC) Data Latch

    Global BC data are seven bits long. The global brightness for all outputs is controlled by the data in the control data latch. The data are used to adjust the constant-current values for the 48-channel constant-current outputs. As explained in the Global Brightness Control (BC) Function section, the BC values are used to adjust the output current from 10% to 100% of the maximum value. When the device is powered on, the BC data are random.

    The global BC data bit assignment in the control data latch is shown in Table 4. See Table 10 for a summary of the BC data value versus set current value.

    Table 4. Global Brightness Control Data Bit Assignment in the Control Data Latch

    CONTROL DATA LATCH BIT NUMBER BIT NAME DEFAULT VALUE CONTROLLED CHANNEL
    351-345 BCR[6:0] N/A (no default value) BC bits[6:0] for red color group channels (OUTR0 to OUTR15)
    358-352 BCG[6:0] BC bits[6:0] for green color group channels (OUTG0 to OUTG15)
    365-359 BCB[6:0] BC bits[6:0] for blue color group channels (OUTB0 to OUTB15)

    8.3.2.7 Function Control (FC) Data Latch

    The FC data latch is 5 bits long. This latch enables the auto display repeat and display timing reset functions, and sets the DC data auto refresh, PWM control mode, and the LSD detection voltage. Each function is selected by the data in the control data latch. When the device is powered on, the FC data are random. The FC data bit assignment in the control data latch is shown in Table 5.

    Table 5. Function Control Data Latch Bit Description

    BIT
    NUMBER    		 BIT
    NAME    		 DEFAULT VALUE
    (Binary)    		 DESCRIPTION
    366 DSPRPT N/A
    (no default value)    		 Auto display repeat mode enable bit
    0 = Disabled, 1 = Enabled
    When this bit is 0, the auto display repeat function is disabled. Each constant-current output is turned on and off for one display period.
    When this bit is 1, each output repeats the PWM control every 65,536 GSCLKs.
    367 TMGRST Display timing reset mode enable bit
    0 = Disabled, 1 = Enabled
    When this bit is 0, the GS counter is not reset and the outputs are not forced off even when a LAT rising edge is input for a GS data write.
    When this bit is 1, the GS counter is reset to 0 and all outputs are forced off at the LAT rising edge for a GS data write. Afterwards, PWM control resumes from the next GSCLK rising edge.
    368 RFRESH Auto data refresh mode enable bit
    0 = Disabled, 1 = Enabled
    When this bit is 0, the auto data refresh function is disabled. The data in the common shift register are copied to the GS data latch at the next LAT rising edge for a GS data write. DC data in the control data latch are copied to the DC data latch at the same time.
    When this bit is 1, the auto data refresh function is enabled. The data in the common shift register are copied to the GS data latch at the 65,536th GSCLK after the LAT rising edge for a GS data write. DC data in the control data latch are copied to the DC data latch at the same time.
    369 ESPWM ES-PWM mode enable bit
    0 = Disabled, 1 = Enabled
    When this bit is 0, the conventional PWM control mode is selected. If the TLC5955 is used for multiplexing a drive, the conventional PWM mode should be selected to prevent excess on or off switching.
    When this bit is 1, ES-PWM control mode is selected.
    370 LSDVLT LSD detection voltage selection bit
    LED short detection (LSD) detects a fault caused by a shorted LED by comparing the OUTXn voltage to the LSD detection threshold voltage. The threshold voltage is selected by this bit.
    When this bit is 0, the LSD voltage is VCC × 70%. When this bit is 1, the LSD voltage is VCC × 90%.

    8.3.3 Status Information Data (SID)

    The status information data (SID) contains the status of the LED open detection (LOD) and LED short detection (LSD). When the MSB of the common shift register is set to 0 and the RFRESH bit in the control data latch is 0, the SID are loaded to the common shift register at the LAT falling edge after the data in the common shift register are loaded to the grayscale data latch. If the common shift register MSB is 1, the SID are not loaded to the common shift register.

    When the MSB of the common shift register is set to 0 and the RFRESH bit in the control data latch is 1, the SID are loaded to the common shift register at the GS counter 0000h just after LAT when the GS data are input. If the common shift register MSB is 1, the SID are not loaded to the common shift register. When the RFRESH bit is 1, the SCLK rising edge must be input with a low-level LAT signal after 65,538 GSCLKs (or more) are input from the LAT rising signal input.

    After being loaded into the common shift register, new SID data cannot be loaded until at least one new bit of data is written into the common shift register. To recheck SID without changing the GS data, reprogram the common shift register with the same data currently programmed into the GS latch. When LAT goes high, the GS data do not change, but new SID data are loaded into the common shift register. LOD and LSD are shifted out of SOUT with each SCLK rising edge. The SID load configuration is shown in Figure 24 and Table 6.

    fc_SID_load_assmt_sbvs237.gifFigure 24. SID Load Configuration

    Table 6. SID Load Description

    COMMON SHIFT REGISTER BIT NUMBER LOADED SID COMMON SHIFT REGISTER BIT NUMBER LOADED SID
    671-0 No data loaded 720 OUTR0 LOD data
    672 OUTR0 LSD data
    (0 = No error, 1 = Error)    		 721 OUTG0 LOD data
    673 OUTG0 LSD data 722 OUTB0 LOD data
    674 OUTB0 LSD data 723 OUTR1 LOD data
    675 OUTR1 LSD data 724 OUTG1 LOD data
    676 OUTG1 LSD data 725 OUTB1 LOD data
    677 OUTB1 LSD data 726 OUTR2 LOD data
    678 OUTR2 LSD data 727 OUTG2 LOD data
    679 OUTG2 LSD data 728 OUTB2 LOD data
    680 OUTB2 LSD data 729 OUTR3 LOD data
    681 OUTR3 LSD data 730 OUTG3 LOD data
    682 OUTG3 LSD data 731 OUTB3 LOD data
    683 OUTB3 LSD data 732 OUTR4 LOD data
    684 OUTR4 LSD data 733 OUTG4 LOD data
    685 OUTG4 LSD data 734 OUTB4 LOD data
    686 OUTB4 LSD data 735 OUTR5 LOD data
    687 OUTR5 LSD data 736 OUTG5 LOD data
    688 OUTG5 LSD data 737 OUTB5 LOD data
    689 OUTB5 LSD data 738 OUTR6 LOD data
    690 OUTR6 LSD data 739 OUTG6 LOD data
    691 OUTG6 LSD data 740 OUTB6 LOD data
    692 OUTB6 LSD data 741 OUTR7 LOD data
    693 OUTR7 LSD data 742 OUTG7 LOD data
    694 OUTG7 LSD data 743 OUTB7 LOD data
    695 OUTB7 LSD data 744 OUTR8 LOD data
    696 OUTR8 LSD data 745 OUTG8 LOD data
    697 OUTG8 LSD data 746 OUTB8 LOD data
    698 OUTB8 LSD data 747 OUTR9 LOD data
    699 OUTR9 LSD data 748 OUTG9 LOD data
    700 OUTG9 LSD data 749 OUTB9 LOD data
    701 OUTB9 LSD data 750 OUTR10 LOD data
    702 OUTR10 LSD data 751 OUTG10 LOD data
    703 OUTG10 LSD data 752 OUTB10 LOD data
    704 OUTB10 LSD data 753 OUTR11 LOD data
    705 OUTR11 LSD data 754 OUTG11 LOD data
    706 OUTG11 LSD data 755 OUTB11 LOD data
    707 OUTB11 LSD data 756 OUTR12 LOD data
    708 OUTR12 LSD data 757 OUTG12 LOD data
    709 OUTG12 LSD data 758 OUTB12 LOD data
    710 OUTB12 LSD data 759 OUTR13 LOD data
    711 OUTR13 LSD data 760 OUTG13 LOD data
    712 OUTG13 LSD data 761 OUTB13 LOD data
    713 OUTB13 LSD data 762 OUTR14 LOD data
    714 OUTR14 LSD data 763 OUTG14 LOD data
    715 OUTG14 LSD data 764 OUTB14 LOD data
    716 OUTB14 LSD data 765 OUTR15 LOD data
    717 OUTR15 LSD data 766 OUTG15 LOD data
    718 OUTG15 LSD data 767 OUTB15 LOD data
    719 OUTB15 LSD data 768 No data loaded

    8.3.4 LED Open Detection (LOD)

    LOD detects a fault caused by an LED open circuit or a short from OUTXn to ground with low resistance by comparing the OUTXn voltage to the LOD detection threshold voltage (0.3 V, typically). If the OUTXn voltage is lower than the threshold voltage when OUTXn is on, that output LOD bit is set to 1 to indicate an open LED. Otherwise, the LOD bit is set to 0. LOD data are only valid for outputs that are programmed to be on. LOD data are latched into the LOD, LSD data latch at the 33rd GSCLK. LOD data for outputs programmed to be off at the 33rd GSCLK are always 0. The LED open detection circuit is shown in Figure 25 and Table 7 lists an LOD truth table. Refer to Figure 26 for an LOD read timing diagram.

    8.3.5 LED Short Detection (LSD)

    LSD data detect a fault caused by a shorted LED between LED terminals by comparing the OUTXn voltage to the LSD detection threshold voltage level set by LSDVLT in the control data latch. If the OUTXn voltage is higher than the programmed voltage when OUTXn is on, the corresponding output LSD bit is set to 1 to indicate a shorted LED. Otherwise, the LSD bit is set to 0. LSD data are only valid for outputs that are programmed to be on. LSD data are latched into the LOD, LSD data latch at the 33rd GSCLK. LSD data for outputs programmed to be off at the 33rd GSCLK are always 0. The LSD open detection circuit is shown in Figure 25 and Table 7 lists an LSD truth table. Refer to Figure 26 for an LSD read timing diagram.

    dg_LOD_LSD_circuit_sbvs237.gifFigure 25. LOD and LSD Circuit

    Table 7. LOD and LSD Truth Table

    SID DATA CONDITION
    LOD LSD
    0 LED is not opened (VOUTXn > VLOD) LED is not shorted (VOUTXn ≤ VLSD)
    1 LED is open or shorted to GND (VOUTXn ≤ VLOD) LED is shorted between anode and cathode, or shorted to higher voltage side (VOUTXn > VLSD)
    td_LOD_LSD_read_sbvs237.gifFigure 26. LOD and LSD Read and Load Timing Diagram

    8.3.6 Noise Reduction

    Large surge currents may flow through the device and the board on which the device is mounted if all 48 outputs turn on simultaneously at the start of each GS cycle. These large current surges can introduce detrimental noise and electromagnetic interference (EMI) into other circuits. The TLC5955 independently turns the outputs on with a series delay for each group to provide a soft-start feature. The output current sinks are grouped into eight groups. The first output group that is turned on or off are OUTR4, OUTG4, OUTB4, OUTR11, OUTG11, and OUTB11; the second output group is OUTX0 and OUTX15; the third output group is OUTX5 and OUTX10; the fourth output group is OUTX1 and OUTX14; the fifth output group is OUTX2 and OUTX13; the sixth output group is OUTX6 and OUTX9; the seventh output group is OUTX3 and OUTX12; and the eighth output group is OUTX7 and OUTX8. Each output group is turned on and off sequentially with a small delay between groups.

    8.4 Device Functional Modes

    8.4.1 Maximum Current Control (MC) Function

    The maximum output current per channel, IOLCMax, is programmed by the MC data and is set with the serial interface. IOLCMax is the largest current for each output. Each OUTXn sinks the IOLCMax current when they turn on and the dot correction and global brightness control data are set to the maximum value of 7Fh (127d).

    When the device is powered on, the MC data are set to 0. MC data should be changed when all constant-current outputs (OUTXn, where X = R, G, or B; n = 0 to 7) are off. MCX = 6 and MCX = 7 are used when VCC is greater than 3.6 V. The same MC data must be written twice to change the maximum constant-current output. Table 8 shows the characteristics of the constant-current sink versus the maximum current (MC) control data.

    Table 8. Maximum Constant-Current Output versus MC Data

    MCX(2) DATA IOLCMax (mA), OUTXn(3)
    BINARY DECIMAL HEX
    000 (default) 0 (default) 0 (default) 3.2
    001 1 1 8.0
    010 2 2 11.2
    011 3 3 15.9
    100 4 4 19.1
    101 5 5 23.9
    110(1) 6 6 27.1
    111(1) 7 7 31.9
    (1) MCX7 and MCX6 can be used when VCC is greater than 3.6 V.
    (2) X = R, G, or B.
    (3) X = R, G, or B. n = 0 to 15.

    8.4.2 Dot Correction (DC) Function

    The TLC5955 can individually adjust the output current of each channel (OUTx0 to OUTx15, where x is R, G, or B) by using DC. The DC function allows the brightness deviations of the LEDs connected to each output to be individually adjusted. Each output DC is programmed with a 7-bit word, so the value is adjusted with 128 steps within the range of 26.2% to 100% of IOLCMax. DC data are programmed into the TLC5955 with the serial interface. When the device is powered on, the DC data in the control latch contains random data. Therefore, DC data must be written to the DC data latch before turning the constant-current outputs on. Table 9 summarizes the DC data value versus the set current value.

    Table 9. DC Data versus Current Ratio and Set Current Value

    DCXn(3) DATA BC DATA (Hex) RATIO OF OUTPUT CURRENT TO IOLCMax (%) IOUT (mA)
    (MC = 7, typical)    		 IOUT (mA)
    (MC = 0, typical)
    BINARY DECIMAL HEX
    000 0000 0 00 7F 26.2 8.36 0.84
    000 0001 1 01 7F 26.7 8.54 0.86
    000 0010 2 02 7F 27.3 8.73 0.88
    — — — — — — —
    111 1101 125 7D 7F 98.8 31.5 3.16
    111 1110 126 7E 7F 99.4 31.7 3.18
    111 1111 127 7F 7F 100.0 31.9 3.20

    8.4.3 Global Brightness Control (BC) Function

    The TLC5955 has the ability to adjust the output current of all constant-current outputs of each color group (OUTR0 to OUTR15, OUTG0 to OUTG15, and OUTB0 to OUTB15) simultaneously to the same current ratio. This function is called global brightness control (BC). The BC function allows the global brightness of LEDs connected to the output to be adjusted. All outputs of each color group can be adjusted in 128 steps from 10% to 100% of the maximum output current, IOLCMax. BC data are programmed into the TLC5955 with the serial interface. When the BC data change, the output current also changes immediately. When the device is powered on, the BC data contain random data. Table 10 summarizes the BC data versus the set current value.

    Table 10. BC Data versus Constant-Current Ratio and Set Current Value

    BCX(2) DATA DCXn(3) DATA (Hex) RATIO OF OUTPUT CURRENT TO IOLCMax(%) IOUT (mA)
    (MC = 7, typical)    		 IOUT (mA)
    (MC = 0, typical)
    BINARY DECIMAL HEX
    000 0000 0 00 7F 10.0 3.19 0.32
    000 0001 1 01 7F 10.7 3.42 0.34
    000 0010 2 02 7F 11.4 3.64 0.37
    — — — — — — —
    111 1101 125 7D 7F 98.6 31.5 3.15
    111 1110 126 7E 7F 99.3 31.7 3.18
    111 1111 127 7F 7F 100.0 31.9 3.20

    8.4.4 Grayscale (GS) Function (PWM Control)

    The TLC5955 can adjust the brightness of each output channel using a pulse width modulation (PWM) control scheme. The architecture of 16 bits per channel results in 65,536 brightness steps, from 0% up to 100% brightness.

    The PWM operation for OUTn is controlled by a 16-bit grayscale (GS) counter. The GS counter increments on each GS reference clock (GSCLK) rising edge. The GS counter resets to 0000h when the LAT rising signal for a GS data write is input with the display timing reset mode enabled.

    The TLC5955 has two types of PWM control: conventional PWM control and enhanced spectrum (ES) PWM control. The conventional PWM control can be selected when the ESPWM bit in the control data latch is 0. The ES PWM control is selected when the ESPWM bit is 1. The conventional PWM control should be selected for multiplexing a drive. The ES-PWM control should be selected for a static drive.

    The on-time (tOUT_ON) of each output (OUTn) can be calculated by Equation 2.

    Equation 2. tOUT_ON (ns) = tGSCLK (ns) × GSXn

    where:

  • TGSCLK = one GS clock period,
  • GSXn = the programmed GS value for OUTXn (GSXn = 0d to 65535d),
  • X = R, G, or B for the red, green, or blue color group, and
  • n = 0 to 15.

    • Table 11 summarizes the GS data values versus the output on-time duty cycle. When the device powers up, all OUTXn are forced off, the GS counter initializes to 0000h, and the status remains the same until GS data are written. After that, each OUTXn on and off status can be controlled by GS data and GSCLK.

    Table 11. Output Duty Cycle and On-Time versus GS Data

    GS DATA ON-TIME DUTY (%) GS DATA ON-TIME DUTY (%)
    DECIMAL HEX DECIMAL HEX
    0 0 0 32768 8000 50.000
    1 1 0.002 32769 8001 50.002
    2 2 0.003 32770 8002 50.003
    3 3 0.005 32771 8003 50.005
    — — — — — —
    8191 1FFF 12.498 40959 9FFF 62.498
    8192 2000 12.500 40960 A000 62.500
    8193 2001 12.502 40961 A001 62.502
    — — — — — —
    16381 3FFD 24.996 49149 BFFD 74.995
    16382 3FFE 24.997 49150 BFFE 74.997
    16383 3FFF 24.998 49151 BFFF 74.998
    16384 4000 25.000 49152 C000 75.000
    16385 4001 25.002 49153 C001 75.002
    16386 4002 25.003 49154 C002 75.003
    16387 4003 25.005 49155 C003 75.005
    — — — — — —
    24575 5FFF 37.498 57343 DFFF 87.498
    24576 6000 37.500 57344 E000 87.500
    24577 6001 37.502 57345 E001 87.502
    — — — — — —
    32765 7FFD 49.995 65533 FFFD 99.995
    32766 7FFE 49.997 65534 FFFE 99.997
    32767 7FFF 49.998 65535 FFFF 99.998

    8.4.4.1 Conventional PWM Control

    The first GS clock rising edge increments the GS counter by one and switches on all outputs with a non-zero GS value programmed into the GS data latch. Each additional GS clock rising edge increases the corresponding GS counter by one.

    The GS counter keeps track of the number of clock pulses from the respective GS clock inputs. Each output stays on while the counter is less than or equal to the programmed GS value. Each output turns off at the GS counter value rising edge when the counter becomes greater than the output GS latch value. Figure 27 illustrates the conventional PWM operation.

    td_conv_PWM_oper_sbvs237.gifFigure 27. Conventional PWM Operation

    8.4.4.2 Enhanced Spectrum (ES) PWM Control

    In this PWM control, the total display period is divided into 128 display segments. The total display period is the time from the first GS clock (GSCLK) to the 65,536th GSCLK input. Each display segment has a maximum of 512 GSCLKs. The OUTXn on-time changes, depending on the 16-bit GS data. Refer to Table 12 for the sequence of information and to Figure 28 for the timing information.

    Table 12. ES PWM Drive Turn On-Time Length

    GS DATA OUTn DRIVER OPERATION
    DECIMAL HEX
    0 0000h Does not turn on
    1 0001h Turns on for one GSCLK period in the first display segment
    2 0002h Turns on for one GSCLK period in the first and 65th display segments
    3 0003h Turns on for one GSCLK period in the first, 65th, and 33rd display segments
    4 0004h Turns on for one GSCLK period in the first, 65th, 33rd, and 97th display segments
    5 0005h Turns on for one GSCLK period in the first, 65th, 33rd, 97th, and 17th display segments
    6 0006h Turns on for one GSCLK period in the first, 65th, 33rd, 97th, 17th, and 81st display segments
    — — The number of display segments where OUTn is turned on for one GSCLK is incremented by increasing GS data in the following order:
    1 > 65 > 33 > 97 > 17 > 81 > 49 > 113 > 9 > 73 > 41 > 105 > 25 > 89 > 57 > 121 > 5 > 69 > 37 > 101 > 21 > 85 > 53 > 117 > 13 > 77 > 45 > 109 > 29 > 93 > 61 > 125 > 3 > 67 > 35 > 99 > 19 > 83 > 51 > 115 > 11 > 75 > 43 > 107 > 27 > 91 > 59 > 123 > 7 > 71 > 39 > 103 > 23 > 87 > 55 > 119 > 15 > 79 > 47 > 111 > 31 > 95 > 63 > 127 > 2 > 66 > 34 > 98 > 18 > 82 > 50 > 114 > 10 > 74 > 42 > 106 > 26 > 90 > 58 > 122 > 6 > 70 > 38 > 102 > 22 > 86 > 54 > 118 > 14 > 78 > 46 > 110 > 30 > 94 > 62 > 126 > 4 > 68 > 36 > 100 > 20 > 84 > 52 > 116 > 12 > 76 > 44 > 108 > 28 > 92 > 60 > 124 > 8 > 72 > 40 > 104 > 24 > 88 > 56 > 120 > 16 > 80 > 48 > 112 > 32 > 96 > 64 > 128.
    127 007Fh Turns on for one GSCLK period in the first to 127th display segments, but does not turn on in the 128th display segment
    128 0080h Turns on for one GSCLK period in all display segments (first to 128th)
    129 0081h Turns on for two GSCLK periods in the first display period and for one GSCLK period in all other display periods
    — — The number of display segments where OUTn is turned on for one GSCLK is incremented by increasing GS data in the following order:
    1 > 65 > 33 > 97 > 17 > 81 > 49 > 113 > 9 > 73 > 41 > 105 > 25 > 89 > 57 > 121 > 5 > 69 > 37 > 101 > 21 > 85 > 53 > 117 > 13 > 77 > 45 > 109 > 29 > 93 > 61 > 125 > 3 > 67 > 35 > 99 > 19 > 83 > 51 > 115 > 11 > 75 > 43 > 107 > 27 > 91 > 59 > 123 > 7 > 71 > 39 > 103 > 23 > 87 > 55 > 119 > 15 > 79 > 47 > 111 > 31 > 95 > 63 > 127 > 2 > 66 > 34 > 98 > 18 > 82 > 50 > 114 > 10 > 74 > 42 > 106 > 26 > 90 > 58 > 122 > 6 > 70 > 38 > 102 > 22 > 86 > 54 > 118 > 14 > 78 > 46 > 110 > 30 > 94 > 62 > 126 > 4 > 68 > 36 > 100 > 20 > 84 > 52 > 116 > 12 > 76 > 44 > 108 > 28 > 92 > 60 > 124 > 8 > 72 > 40 > 104 > 24 > 88 > 56 > 120 > 16 > 80 > 48 > 112 > 32 > 96 > 64 > 128.
    255 00FFh Turns on for two GSCLK periods in the first to 127th display segments and turns on one GSCLK period in the 128th display segment
    256 0100h Turns on for two GSCLK periods in all display segments (first to 128th)
    257 0101h Turns on for three GSCLK periods in the first display segments and for two GSCLK periods in all other display segments
    — — The number of display segments where OUTn is turned on for one GSCLK is incremented by increasing GS data in the following order:
    1 > 65 > 33 > 97 > 17 > 81 > 49 > 113 > 9 > 73 > 41 > 105 > 25 > 89 > 57 > 121 > 5 > 69 > 37 > 101 > 21 > 85 > 53 > 117 > 13 > 77 > 45 > 109 > 29 > 93 > 61 > 125 > 3 > 67 > 35 > 99 > 19 > 83 > 51 > 115 > 11 > 75 > 43 > 107 > 27 > 91 > 59 > 123 > 7 > 71 > 39 > 103 > 23 > 87 > 55 > 119 > 15 > 79 > 47 > 111 > 31 > 95 > 63 > 127 > 2 > 66 > 34 > 98 > 18 > 82 > 50 > 114 > 10 > 74 > 42 > 106 > 26 > 90 > 58 > 122 > 6 > 70 > 38 > 102 > 22 > 86 > 54 > 118 > 14 > 78 > 46 > 110 > 30 > 94 > 62 > 126 > 4 > 68 > 36 > 100 > 20 > 84 > 52 > 116 > 12 > 76 > 44 > 108 > 28 > 92 > 60 > 124 > 8 > 72 > 40 > 104 > 24 > 88 > 56 > 120 > 16 > 80 > 48 > 112 > 32 > 96 > 64 > 128.
    65479 FEFFh Turns on for 511 GSCLK periods in the first to 127th display segments, but only turns on for 510 GSCLK periods in the 128th display segment
    65480 FF00h Turns on for 511 GSCLK periods in all display segments (first to 128th)
    65481 FF01h Turns on for 512 GSCLK periods in the first display period and for 511 GSCLK periods in the second to 128th display segments
    — — —
    65534 FFFEh Turns on for 512 GSCLK periods in the first to 63rd and 65th to 127th display segments; also turns on for 511 GSCLK periods in the 64th and 128th display segments
    65535 FFFFh Turns on for 512 GSCLK periods in the first to 127th display segments but only turns on for 511 GSCLK periods in the 128th display segment
    td_ES_PWM_oper_sbvs237.gifFigure 28. ES PWM Operation

    8.4.4.3 Auto Display Repeat Function

    This function can repeat the total display period as long as GSCLK is present, as shown in Figure 29. This function is switched on or off by the content of the DSPRPT bit in the control data latch.

    When the DSPRPT bit is 1, auto display repeat is enabled and the entire display period repeats. When the DSPRPT bit is 0, auto display repeat is disabled and the entire display period only executes one time after a LAT signal rising edge is input for GS data writes when the display timing reset is enabled.

    td_auto_disp_repeat_sbvs237.gifFigure 29. Auto Display Repeat Function

    8.4.4.4 Display Timing Reset Function

    The display timing reset function allows initializing the display timing with a LAT rising edge. This function can be switched on or off with the TMGRST bit in the control data latch. When the TMGRST bit is 1, the GS counter is reset to 0 and all outputs are forced off at the LAT rising edge for a GS data write. Furthermore, the 768-bit GS data latch is updated with the data from the common shift register and the 336-bit DC data latch is updated with the DC data in the 371-bit control data latch. When the TMGRST bit is 0, the GS counter is not reset and the outputs are not forced off, even if a LAT rising edge is input. A timing diagram for this function is shown in Figure 30.

    td_disp_timing_reset_sbvs237.gifFigure 30. Display Timing Reset Function (DSPRPT = 1, TMGRST = 1, and RFRESH = 0)

    8.4.4.5 Auto Data Refresh Function

    This function delays updating the grayscale (GS) and dot correction (DC) data until the end of one entire display period. If both DC data and GS data are written by the end of an entire display period, the input DC data are held in the control data latch and the GS data are held in the common shift register. Both DC and GS data are copied to the 336-bit DC data latch and 768-bit GS data latch at the end of an entire display period. The data latches are used for the next display period. GS data are directly copied from the common shift register to the GS data latch. Therefore, GS data must be written after the DC data are written. Furthermore, the GS data in the common shift resistor must not be changed until all data are copied to the GS data latch. Figure 31 and Figure 32 show timing diagrams for this function.

    td_auto_data_refresh1_sbvs237.gifFigure 31. Auto Data Refresh Function 1 (DSPRPT = 1, TMGRST = 0, and RFRESH = 1)
    td_auto_data_refresh2_sbvs237.gifFigure 32. Auto Data Refresh Function 2 (DSPRPT = 1, TMGRST = 0, and RFRESH = 0)