TPS61175: Current Limit

Hi Ottey,

The duty cycle will have an effect on the switch current limit. The switch current limit vs. duty cycle curve is shown in figure 4.

The input voltage, switching frequency has little impact on the switch current limit.

However, our device won't test at full Vin range, duty cycle range because it costs too much effort. 

Please leave enough margin in your design to avoid triggering current limit.

Hope that helps.

Hi Zack

I understand that the value of the Duty cycle changes the current limit.
Can the N-Channel MOSFET current limit fall below 3A when the duty cycle changes?
(If possible, I would be grateful if you could tell me the minimum value of the Current limit when the Duty changes.)

Regards,
Y.Ottey

Hi Ottey,

May I know your application's Vin, Vout, Iout condition? What's the reason that you'd like to know this spec?

Hi Zack

The conditions that our customers are considering are as follows.
Vin = 6.3V
Vout = 11.4V
Iout = about 1A

I would like to know if the current limit threshold does not fall below 3A even if the input / output voltage and duty ratio change from the above conditions due to the effects of inrush current at startup.

Regards,
Y.Ottey

Hi Ottey,

Thank you for the information.

Will the apply the 1A load current during the startup? If not, I think you don't have to be worried about it.

TPS61175 has soft start function which significantly reduces the start-up current spike and output voltage overshoot. When the IC is enabled, the voltage at the SS capacitor clamps the output of the internal error amplifier that determines the duty cycle of PWM control, thereby the input inrush current is eliminated.

Hi Zack

Thank you for your reply.

Sorry for the lack of information.
There is almost no load at startup, and a load of about 1A flows by turning on the connected load (motor) during operation.
(At that time, inrush current may flow and the input / output voltage (Duty ratio) may change.)

I think that the duty ratio changes and the current limit threshold changes, which may cause the value to fall below the current limit minimum value of 3A described in the data sheet.
Therefore, please tell me whether the minimum value of the current limit threshold does not fall below 3A even if the duty ratio is changed.

Best Regardes,

Y.Ottey

Hi Zack

Thank you for your reply.

I understand what you have written.

I have additional questions.
When designing with TPS61175, I am thinking about designing so that it does not exceed the minimum value of the following N-chanel MOSFET Current limit.
In the table below shown in the data sheet, the minimum value of N-chanel MOSFET Current limit is 3A when D = Dmax.
Should I design it so that it does not exceed the minimum value of 3A of the N-chanel MOSFET Current limit described in the data sheet even if it becomes the value of other duty cycles (D ≠ Dmax)?

Regards,
Y.Ottey