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TLC5971: Unstable at 3.3V

May
Genius 9880 points
Part Number: TLC5971

Hi,

One of customer is encountering instability at 3.3V when using the TLC5971. 

Customer is testing the TLC5971RGER LED driver at 3.3V and 5V. For the 5V case they used the schematic in Figure 31 and the schematic in Figure 38 was used for the 3.3V case. The 5V case shows stability over time, but the driver is very unstable at 3.3V (see attached image).

Customer are using a 2.32 kOhm, low temperature drift, resistor to achieve a 21 mA driving current using the schematic in Figure 38. According to them, they also tested the TLC59711 dev. board and found the same issue.

Is there a workaround to make the 3.3 stable or is this normal for 3.3V? 

Regards,
Maynard

  • 0
    TI__Genius 12915 points

    Hi Maynard,

    How about the forward voltage of the LEDs customer used? Taking Figure 7 in datasheet as reference, for 21mA output current, there must be at least 0.5V at output pins. The outputs are current sinks, which need enough voltage for them to work at saturation region to provide precise current. I suppose 3.3V power supply is not enough for Vf + Vsat in customer's condition.