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TLC59461 maximum output current with GS function (Mode=L) after power on

David Huang14292
Prodigy 370 points
Other Parts Discussed in Thread: TLC59461, TLC5941, TLC5940, TLC5943, TLC5944, TLC5946

Hello,

 

TLC59461 is used to drive four LEDs. Vcc=5V.

Mode=L, (pin6) is connected to GND with 0R and R45 is not installed.

XHALF=H

TLC59461 works as GS function. BLANK, XLAT, SCLK, SIN, GSCLK are controlled by MCU.

Five output drive (from OUT8 to OUT12) are connected together to drive Yellow LEDs. 

 

1. After power on, MCU write SIN (000h 000h 000h FFFh FFFh FFFh FFFh FFFh 000h 000h 000h 000h 000h 000h 000h 000h) and then send a pulse of XLAT.

 

The total output current of Yellow LEDs (from OUT8 to OUT12) is about 180mA based on above setting.

 

However, with several times system power on and off, sometimes the maximum Yellow LEDs output current is different from 180mA and it may changes from 100mA to 180mA.9

 

If the maximum output current changes to 150mA with the step 1 after power up. The output current can not increase to more than 150mA by write SIN (000h 000h 000h FFFh FFFh FFFh FFFh FFFh 000h 000h 000h 000h 000h 000h 000h 000h) and the output current can be reduced to less than 150mA by sending different data to SIN.

 

The maximum Yellow LED output current can increase to 180mA only turn-off the system including MCU. The maximum output current remains 150mA by reset MCU or disconnect and reconnect TPS59461 Vcc to +5V.

 

It seems that the maximum Yellow LEDs output current is determined by the first time power up. The output current can be modified to smaller amount current by writing SIN. 

 

Could some one help check whether TLC59461 can work GS function by pulling mode to GND all the time? Is the constant-current driver stage of TLC59461 is the same as that of TLC5941 which is showed in datasheet TLC5941 page 1.

If so, what is the Dot correction register data with Mode=L after power up? How to avoid the difference of maximum output current after several times power off and on?

  • 0
    TI__Mastermind 36110 points
    The TLC5940, TLC5941, TLC5942, TLC5943, TLC5944, TLC5946, TLC59461 ICs do not have a default dot correction value at startup.  Each startup condition can generate a random dot correction (DC) value.  This DC value limits the maximum current per the equations defined in the datasheet.  At power up, the customer must program the DC value before programming the PWM grayscale data and turning on the outputs.
  • 0 in reply to Matthew Day
    Prodigy 20 points

    The TLC5940 has internal EEPROM, that stores the dot correction values. Each startup loads the EEPROM's data to the DC register, so it will be the same every startup. I know it so. Is it right?

     

  • 0 in reply to YoYoFlex
    TI__Mastermind 36110 points

    You are correct that the TLC5940 contains an internal EEPROM to store the dot correction values.  If properly configured with DCPRG connected low, the TLC5940 uses the EEPROM for dot correction.  If DCPRG is tied high, the TLC5940 uses the internal register for dot correction value.  The internal register contains random values at startup.