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TPS92641: Analog Dimming using IADJ-pin

Takashi Yamaguchi
Genius 13290 points
Part Number: TPS92641
Other Parts Discussed in Thread: TPS92692

Hi team,

Could you support the following questions?

1. The d/s describes that " IADJ can be set to any value up to 2.54 V by connecting it to VREF through a resistor divider for static output current settings".  Does this mean that the range of VADJ that can be analog dimming linearly is 0V to 2.54V?

2. According to the E.C table in the d/s, VADJ-MAX is specified as 2.46V(min), so should customer use  VADJ is 0V to 2.46V? 

3. If customer applies a voltage which out of the VADJ range to the IADJ-pin, how behave the TPS92641?

Regards,

Yamaguchi

  • 0
    TI__Mastermind 28655 points

    Hello Yamaguchi,

    1)  Iadj can be set from 0V to 2.54V.  Note that 0V does not mean zero current due to offsets and current ripple, there is a section in the datasheet about true zero current, section 7.3.4.  It should be linear since it is synchronous buck converter.

    2)  No, that is the tolerance range of Vadj.  The typical should be used for calculating the output current.  The minimum and maximum would be used as one of the variables to calculate accuracy.

    3)  It is setting the error amplifier reference to a voltage level.  It will behave the same and try to regulate current to the Vadj set-point.  The LED driver can behave different such as turn-on time to charge an output capacitor since the current level will be different.  And, of course, the LED current will be different.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    TI__Genius 13290 points

    Hi team,

    I received additional question from customer about the IADJ range which can be linearly adjusted the output current. Could you help with the question below?

    According to the 7.2 Functional Block Diagram, there is an internal clamp diode on the IADJ. The clamp voltage varies such 2.46V(min), 2.54V(typ), 2.62V(max).  Therefore, there is possibility that the Vadj is clamped 2.46V(min) when customer applies 2.54V to IADJ-pin. In this case, customer thinks this region(2.46V~2.54V) is not linear. Customer thinks that the maximum linear range is up to 2.46V. Is the customer's understanding correct?

    In the TPS92692 case, the maximum VADJ is less than the clamp voltage(min). Vadj range is 140mV to 2.25V.  IADJ internal clamp voltage is 2.29V(min), 2.40V(typ), 2.55V(max).

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Genius 13290 points

    Hi team,

    Could you please support the question I posted Jul 25?

    Regards,

    Yamaguchi

     

  • 0 in reply to Takashi Yamaguchi
    TI__Mastermind 18890 points

    Hi Takashi-san,

    For the block diagram on TPS92641 and the clamp voltage tolerance:  The clamp voltage tolerance is 2.46V to 2.62V.  So if the clamp is at 2.46V and you applied 2.54V then that region from 2.46V-2.54V the current will be the same since the clamp is at 2.46V so the control is not linear in this region.  So the linearity can only be guarantee for up to close to the 2.46V as you mentioned.

    For the TPS92692 we only guarantee linearity from 0.14V to 2.25V.

    Thanks Tuan