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LM53602-Q1: Switching Mode Transition

Shinichi Yokota
Genius 9715 points
Part Number: LM53602-Q1

Hello,

I'd like to confirm the product concept of LM53602-Q1 regarding its switching mode transition.

  • Even in AUTO mode, a LM53602-Q1 won't switch its switching mode AUTOMATICALLY between PWM and PFM and will be forced to operate in PWM regardless of its load condition UNLESS its input voltage once rises above its threshold of about 6.8 V as shown in Figure 13 of the data sheet. Is it a product concept of this device targeted at automotive applications? In a vehicle, a battery voltage once goes up to about 12 to 14 V when a key is turned on, and I guess this device is designed by taking into account this vehicle behavior.
  • Regarding the reason why the LM53602-Q1 stays in PWM before the input voltage rises above the threshold of about 6.8 V, is it because the regulator has to supply a load current which is enough for the load to quickly become active at the system start-up and PWM can better handle the situation than PFM?

Best regards,
Shinichi Yokota

  • 0
    TI__Expert 6860 points
    Yokota -San ,

    At low input voltages , the internal comp will clamped to higher voltage and device will enter dropout mode ie would reduce frequency of operation and light load PFM mode would be overwritten off .

    ---Ambreesh
  • 0 in reply to Ambreesh Tripathi
    TI__Genius 9715 points

    Ambreesh-san,

    I'm afraid my questions don't ask how the device was designed/built. I suspect that there is a reason for the device to behave like what I mentioned in the previous post and I'm asking how TI considered the issue and implemented a function to solve it - That's what I say, "product concept". Could you confirm why TI implemented the threshold for VIN in the LM53602-Q1 and decided to force it to operate in PWM if the VIN stays lower than the threshold? Again, there should be a reason for it and that's what I'd like to know.

    Best regards,
    Shinichi Yokota

  • 0 in reply to Shinichi Yokota
    TI__Expert 6860 points
    Yokota-San ,

    The feature is implemented so that the light load feature is enabled even at lower input voltages . But beyond a particular threshold , the internal comp will clamped to higher voltage and this input voltage is dependent on the programmed output voltage as shown in Fig 13 .
    For example if you program the output to 6V , the input voltage at which this transition happens will also increase .
    SO specifically it is more to do with the dropout operation then to do with automotive .

    ---Ambreesh
  • 0 in reply to Ambreesh Tripathi
    TI__Genius 9715 points

    Ambreesh-san,

    I'm sorry to say that it doesn't answer my questions at all. Again, what was the background from the market for the feature? is my question. I guess someone in your team who defined LM53602-Q1's specs should know about it.

    Best regards,
    Shinichi Yokota

  • 0 in reply to Shinichi Yokota
    TI__Expert 3840 points
    Hi Yokota-san,

    The final behavior of the device at low VINs that is described in the datasheet was not a planned feature, but a result of the trade-off of the architecture that was chosen to implement the PFM to PWM transition.

    Best Regards,
    -JP