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TLC59283: How about PWM operation via BLANK pin? and OUTn behavior when no load or saturating

Naoyuki H
Prodigy 20 points
Part Number: TLC59283
Other Parts Discussed in Thread: TLC59282EVM-118, TLC59282, TLC5955, TLC59116F

Hi.

I want to use some daisy-chained TLC59283 and also need dimming.

At the first time I designed with some 74LV595A, but I need to minimize space on PCB and open drain drive,

so I'm planning to replace them to TLC59283.

I have 3 questions.

1) I want to use PWM dimming via BLANK pins of all TLC59283, instead of OE pin of74LV595A.

I'm planning 100Hz to 1kHz PWM signal and I guess it's enough slow to tD1(max 100nsec) on datasheet.

Is there any problems in such usage and recommended frequency range?

2)Use output in saturating mode

I will use different color LED within same TLC59283.

In this case, LED brightness vs current is different by color (eg. red and green),

so I want to set LED current limiting by series resistor(s) and  OUTn as simple open drain in saturating mode.

And also, it will decreasing power dissipation of TLC59283.

Is there any problems in such usage?

3) No load operation

I will use some TLC59283 with daisy-chain, but there will be some unused OUTn(s).

 I found description below in manual of TLC59282EVM-118, page 6;

>>>Do not operate without LED loads. The TLC59282 outputs are bipolar and can draw high ICC current when no load is connected.

I wonder this issue occurs only with TLC59282, and not occurs with TLC59283, since it has CMOS outputs.

Is that correct?

Thanks and Best Regards,

Naoyuki

  • +1
    TI__Genius 14925 points

    Hi Naoyuki,

    1. It is possible to achieve 100Hz to 1kHz PWM through BLANK pin. You should follow t_WH2 and t_WL2 from RECOMMENDED OPERATING CONDITIONS from the datasheet (Page 3). However, I should mention that this is not the typical usage of BLANK pin.
    2. The saturation usage as you mentioned is not recommended. TLC59283 is not an open-drain LED driver. In normal usage of TLC59283, the user should avoid such saturation and leave enough headroom voltage for the current sinks to function well. Consider using one TLC59283 for all red LEDs and another one for all green LEDs.
    3. The datasheet does not specify that TLC59283 has CMOS channel output. If there are unused channels, you can leave those channels floating. You should always write '0' to unused channels to turn them off.
    4. Some issues in your schematic:
      1. The IREF pin can't be left floating. You must connect an external resistor between IREF and GND.
      2. The GND pin should be connected to the ground.
      3. Check your SIN pin and SCLK pin connection.
    5. Could you tell me what is your end equipment / spec and what effects do you want to achieve with our device? I need more information to make a better suggestion for you.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 20 points

    Hi Steven,

    Thank you very much for your reply.

    1. I understand as possible but not typical.

    2. I also need 2-colored type (red and green in 1chip), and I found that this device is not match for such application.

    3. I had misunderstood Figure 5 on datasheet, maybe Nch sink driver and Pch pre-charge as CMOS output.

    4. I draw my schematic focused on question in a hurry.

    I should check enough in actual design, thanks.

    5.Finally I turned back to 74LV595A, because I need power-on reset function and PWM Dimming.

    Though I also consider about 74HCS595, CMOS output will be acceptable with some design change.

    But, I could learn about this device and I want to try next challenge.

    Thank you and Best Regards,

  • 0 in reply to Naoyuki H
    TI__Genius 14925 points

    Hi Naoyuki,

    You are welcome. Feel free to contact me if you have any further needs and I am willing to help.

    Just for your reference:

    • We have devices like TLC5955, which has the internal PWM timing controller, cascading capability and register settings to program current for each channel output.
    • We also have devices like TLC59116F, which has open-drain outputs and internal power-on reset feature.

    Best Regards,

    Steven