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LM5022: VCC output

Steven LeBlanc
Prodigy 30 points
Part Number: LM5022

The datasheet identifies this pin as the output of an internal regulator and declares that it must be bypassed. However, under Recommended Operating Conditions, connection of an external voltage between 7.5V and 14V seems implied. Under Electrical Characteristics, a minimum of 5V is specified for 6V <= Vin <= 60V, but no maximum, and a range of 6.6V to 7.4V is specified if 10V <= Vin <= 60V. However, a test condition on Icc in the next line below declares Vcc = 10V; which is outside the latter range. Altogether, the Vcc specs are extraordinarily confusing without additional explanation. I need to discuss with a knowledgeable applications engineer. How do I contact such an individual at TI?

  • 0
    TI__Guru* 78060 points
    Hi Steve,
    Thank you for your interests in the Lm5022. Yes the VCC pin is the output pin of the internal LDO, and it can be supplied externally if the voltage is limited between 7.5V and 14V. Lower than 7.5V may cause overloading at the pin because the LDO max output is 7.4V and a constant voltage source at the VCC pin will pull excessive current from the VCC pin. Higher than 14V may cause damage because it exceeds the max voltage rating of the pin.

    Regarding 6V<= Vin <10V, the max VCC will not exceed the voltage specified for 0V <= Vin <= 60V. Note it is a LDO so the min here is critical info.

    For the ICC next line, it is defined as the current taken by the IC (flowing into the IC) when VCC=10V is supplied. This current supplies the oscillator and most internal logic, but not switching driver current.

    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    Prodigy 30 points

    Hi Youhao,

    Thank you for replying. I still feel as though I'm missing something, so I'll restate what I think you're saying so that you can correct my understanding:

    The Vcc pin is an output that supplies at least 5V when Vin is between 6V and 10V, and supplies between 6.6V and 7.4V thereafter. This output can source external circuitry (i.e. capacitor and additional load). However, any external circuitry added that prevents the capacitor from being charged to at least 5V will effectively disable the controller. For example, the Icc-lim specification implies that if I try to draw 35mA therefrom, the Vcc output pin will likely remain near 0V and the controller will never be enabled. Alternatively, if I apply a source voltage to this pin between 7.5V and 14V, the internal LDO regulator will be 'disabled' in the sense that the external source will then provide bias for the internal gate drive and control circuits (per Note (2) of Table 6.5 on the datasheet). However, if this external source supplies a voltage lower than 7.5V, then the internal LDO regulator will not be 'disabled' in this fashion and the difference in source voltages (i.e. internal and external) will be applied across the respective output impedances and may result in excessive current if Vin is sufficiently high.

    Best regards,

    Steven

  • 0 in reply to Steven LeBlanc
    TI__Guru* 78060 points

    Hi Steve,

    You understanding is basically correct.  Just two things to clarify: 

    (1) You may not be able to draw 35mA from Vcc.  The VCC loading capability to external circuit can be much smaller.  The 35mA includes both the internal use, which is mainly the driver,  and the external load if applicable.

    (2) When you apply a source voltage to the VCC pin lower than 7.5V, the LDO MAY or MAY NOT be disabled, depending on the actual internal VCC setting point. If the internal LDO is not disabled, and if your external source is not fixed and no Or-ing diode is used to feed VCC pin, then either the LDO and the external source to share the total VCC load (driver and also external circuit), or the LDO may supply all power.  In the later case, when LDO supplies all power, and the 35mA limit should be in play.  If Vin is high, the LDO will have much loss.

    Thanks,

    Youhao Xi