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TLV62130: About 100% Duty-Cycle Operation

Tao_2199
Genius 5770 points
Part Number: TLV62130

Hello,

 

Regarding to 100% Duty-Cycle Operation on TLV62130, my customer is asking some question.

(Question)

(1) According to formula(3) on datasheet page11, the minimum input voltage is following.

VIN(min) = VOUT(min) + IOUT(RDS(on) +RL )

For example, VOUT(min)=3.8V, Iout=.1.1A, Rds(on) =0.09 ohm, inductor(22uH) DCR=0.035ohm -> VIN(min)=3.93V

In this case, when input is less than 3.93V (< 3.93V), device become to 100% Duty-Cycle Operation mode.

My understanding is correct?

 

(2) In case of the input voltage is crossed to output voltage (Normal Operation <-> 100% Duty-Cycle Operation),

Is there any possible problem on output ? (For example, output accuracy ,regulation )

Or is there other possible problem?

 

(3) Do you have some information of 100% Duty-Cycle Operation more detail?

(Application Note.)

 

Regards,

Tao2199

  • 0
    TI__Expert 3465 points

    Hello Tao,

    thanks for inquiring us on this topic.

    1)Your understanding is correct.

    2)When in 100% mode, the device basically keeps the high side mosfet ON. Hence the output voltage is not regulated and equals (typically):

     VOUT= VIN - IOUT*(HS_RDS(on) +RL)

    3)100% mode on this device is as straightforward as explained in the datasheet:

    "The duty cycle of the buck converter is given by D=Vout/Vin and increases as the input voltage comes close to the output voltage. In this case, the device starts 100% duty cycle operation turning on the high-side switch 100% of the time. The high-side switch stays turned on as long as the output voltage is below the internal setpoint. This allows the conversion of small input to output voltage differences, for example, for longest operation time of battery-powered applications. In 100% duty cycle mode, the low-side FET is switched off."

  • 0 in reply to Emmanuel Granatello
    Genius 5770 points

    Hello Emmanuel,

     

    Thank you for reply.

    I have additional question.

    When the input voltage is crossed to output voltage (Normal Operation <-> 100% Duty-Cycle Operation),

    is there possible that output will become unstable ?

    I think that it is not feedback control at 100% Duty-Cycle Operation. If so, the output will be unstable depending on crossing condition.

    My understanding is correct?

     

    Regards,

    Tao2199

  • 0 in reply to Tao_2199
    TI__Expert 3465 points
    Hello Tao,

    when the HS mosfet is turned on all the time, the circuit can be reduced to the vin source connected to the LC filter. This system is asymptotically stable by nature. The only effect on the Vout is that it's DC voltage get's dropped by the RDSon of the HSmosfet and the DCR of the inductor times the load current.