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LP5860T: Questions about LP5860T.

Kazuya Nakai59
Guru 21505 points
Part Number: LP5860T
Other Parts Discussed in Thread: LP5860

Tool/software:

Hello guys,

One of my customers is going to evaluate LP5860T (Max current 100mA version) for their new products.

At this moment, they have the following questions.
Could you please give me your reply?

Q1.
Can LP5860T operate without any problem when the constant current at CSx pin is set to 100mA and PWM is 100% with 5V VLED?
Is any derating needed? Or is there any concerning point they should care?
Is it the device temperature?

Q2.
How much is Rsw(High-side PMOS ON resistance) when Isw is 1.8A(100mA*18ch)?
They didn't find the data in LP5860T datasheet. They concern that larger voltage drop would be occurred at SWx
because Isw is larger than LP5860 (Max current 50mA version).
The datasheet says that Vsat of CSx is 0.8V. If SWx voltage drop from VLED is 1V, the applied voltage to LED becomes 3.2V(5V-0.8V-1V).
They think that LED which has Vf less than 3,2V should be used for the case.

Your reply would be much appreciated.

Best regards,
Kazuya. 

  • 0
    TI__Expert 5560 points

    Hi Kazuya,

    For your questions please find my answers below.

    1. There is not special derating needed. How many LEDs will be used in the application? The temp rise may need to be considered based on the power consumption on the LED driver multiplies the RθJA (31.4). The power consumption on the LED driver are mainly introduced by the 2 parts below,
      1. Rdson of the internal high side FET
      2. Current sinks, which power consumption  = Voltage on the CS * total current, where the voltage on the CS = VLED -  voltage drop on the FET - LED forward voltage
    2. Yes, your calculation is correct. And we can still take the Rdson as 450m ohm to do the calculation. 

    Best regards,

    Felix