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TPS61230 Zero Duty Cycle Mode

Wolff
Prodigy 50 points

Design scenario:  A 3.3V battery is wired to Vin of the regulator, with an output voltage set a little higher (e.g. 4V), approximately 1uH inductor in use, and about 100uF capacitance present on Vin and Vout. Vout is wired directly to the load 

 

A slightly higher (e.g. 4.2V) voltage source or power supply will for some of the time be wired directly to Vout and the load. According to the datasheet, section 8.4.3 "Zero Duty Cycle Mode" :

 

When the input voltage is lower than VOUT + 0.24 V and VOUT is higher than the nominal output voltage, the device automatically changes to a Zero Duty Cycle Mode. In Zero Duty Cycle Mode, the rectifying switch is constantly turned on and the low side switch is turned off.

 

This will result in the rectifying switch being constantly turned on, and thus Vout being connected directly to the battery in this case, resulting in massive current and possible failure of the battery and/or device. Is this correct or is the datasheet in error ?

  • 0
    TI__Mastermind 46905 points
    hi
    the device will enter Zero duty mode when VOUT is higher than the setting voltage. in your application, VIN=4.2V, VOUT_set=4V, so the device will enter Zero Duty Mode if the load current is not high enough to cause the voltage drop 0.24V. at this mode, VOUT is approx. 4.2V at no load condition.

    but i don't get your meaning of "resulting in massive current and possible failure of the battery and/or device". how this mode resulting in massive current.

    thanks
    Jasper Li