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TPS62130A-Q1: Pre-Bias Operation Scheme of High-Side and Low-Side Switches

Part Number: TPS62130A-Q1
Other Parts Discussed in Thread: TPS62130A, TPS62812-Q1, TPS62097-Q1

Dear tech support team,

I would like to apply the PMIC for core voltage regulation.

I would like to understand, how the regulator switches start to operate, when the pre-bias voltage is below the target voltage. 

In the Datasheet (DS) I did not understand clearly how the mechanism is working. For me it is important to know, if  there is some unintended current sourcing by the PMIC due to enabled low-side switches.

Regards,

  • Swen,

    TPS6213A  inhibits switching of both the high side and low side FETs as long as the internal ramp voltage is below the pre-bias voltage.  TPS62130A uses the VOS pin to directly monitor the output voltage.  When switching does start, the duty cycle will be that which is required to start up from the pre-bias level.

    For context, let me explain operation of devices without pre-bias features.  If a normal synchronous buck were to start up into pre-bias, the fed back voltage at the inverting error amp input would be much higher than the slow start voltage at the non-inverting input.  This would cause the low side FET to turn on constantly to discharge the pre-bias voltage.  During this time the inductor current will ramp negative, possibly to a very large negative value.  The design of TPS62130A prevents this from happening.

  • Hi John,

    thanks for you prompt feedback.

    Can you kindly provide scope screenshots, which show no sinking is caused in my use case?
    I  assume all TPS with pre-bias feature and the added soft start have the same behavior.
    I would be especially interesting to see, when the pre-bias voltage is at 95% of the target level.
    It also important to know, if the high-side switch would start at first instead of the low-side switch.
    by the way I was actually expecting that the low-side switch would stay off until target level is reached.


    Regards,
    Swen

  • Swen,

    There are some pre-bias start up waveforms in this users guide:

    I cab assure you there is no sinking of current as neither the high side or low side is switching prior to the start of the ramp up from the pre-biased voltage.  The high side will switch on first.

    Also it is not safe to assume that all TI devices behave the same in pre-bias conditions.  You would need to read each data sheet carefully.

    I may be able to provide additional waveforms, but probably not any time soon.  Let me know.

  • Hello John,

    the devices TPS62812-Q1 and TPS62097-Q1 (both series) are also interesting because of the feature forced PWM.
    Can you explain, if the output discharge is integrated into the PMIC output line. The block diagram does not show, if this feature could be disabled / removed.

    Regards

  • Swen,

    While I do not support those low input voltage devices, I can answer.  The output discharge resistor is internally connected to the VOS pin, which is directly connected externally to the output voltage.  Besides when EN is  low, the output discharge function will be activated during hiccup current limit, over temperature protection and UVLO.  It is not possible to turn this feature off.