TPS61240 Overload Current / Maximum Output Current

Q: TPS61240 Overload Current / Maximum Output Current by 4339

Hi Experters,

We are trying to increase TPS6124x output load and find they will limit output current and no switch anymore.

But we can't confirm this operation is normal or abnormal, need your confimation.

BTW, we have two questions in below list.

1.Does TPS61241 also behave the current limit as TPS61240 when overloading? If yes, how about the current limit level? (240 is about 80 mA when Vin=2.7V and Vout=5V) 

2.In the condition Vin=2.7V and Vout=5V, what is TPS61241 maximum output current rating? How much current it can drive?

Thank you and Regards

A: Re: TPS61241 overloading behave by 10449

The TPS61240 and TPS61241 have identical behavior except for maximum output current. 

When the TPS61240 or TPS61241 opreate into a short circuit, the IC delivers a constant current to the short circuit.  This behavior is identical to startup where the IC delivers a constant current with no switching until Vout reaches Vin.    This current varies with output voltage.   The TPS61240 datasheet startup figure (fig 14) shows the constant current vs output voltage.  Both ICs behave this way

The TPS61240 datasheet equation 1 helps calculate the maximum output current. Note that datasheet dated May 2009 omitts the efficiency term.  The calculated maximum current must be multiplied by efficiency to get the correct value.  Using the minimum TPS61240 valley current of 500mA, a switching frequency of 3.75MHz, efficiency of 0.80, and inductor value of 1uH,   with Vin=2.7V and Vout=5V, I calculate the maximum current to be 288mA.  This closely agrees with datasheet figure 1.   Substituting 600mA for the TPS61241 valley current, I calculate a maximum current of 331mA.