TPS61230: Zero Duty cycle condition

Hi Sasaki,

When Vin is higher than programmed Vout, the device works at zero duty cycle mode. High side switch is always on so Vout will rises higher than programmed Vout too. That's the meaning of zero duty cycle definition: Vout< Vin< Vout+0.24V and Vout> Vout_nom.

The voltage drop between Vin and Vout depends on the high side switch on resistance. So maximum voltage drop will be Vin-Vo=Io*Rdson= 2A*100mohm=0.2V if the Io_max=2A. 

Liu-san,

I understood Vin voltage becomes lower than Vout+0.24V in Zero duty mode because Io*Rdson doesn't become larger 0.24V.

In Zero duty mode, is current limited by ILIM_pre?

Best Regards,
Kohei Sasaki

Liu-san,

TPS61230 ILIM_sw is 4A min.

When Iout is 4A in Zero duty mode, I think Vin-Vout drop becomes 0.3V. (Rdson is 75m ohm)

This is out of range of Zero duty condition.

In this case, how does the device operate? Is it keep zero duty mode?

Best Regards,
Kohei Sasaki

Liu-san,

Thank you for your reply.

I understood device becomes zero duty mode when Vin voltage is higher than Vout setting voltage.

Best Regards,
Kohei Sasaki