TPS62736 questions

1. The datasheet states the typical value of the switch frequency is 2MHz, however, the actural frequcny will not be exact of the the typical value listed.
2. Where do you measure the input voltage and output voltage. Please measure them as close to the IC's IN and OUT pin as possible. There will be a voltag drop from your power supply to the IN pin of the IC.
3. The max cycle by cycle current limit of the inductor for TPS62736 is listed in the electrical characteristics table, which is 100mA.
4. Major Switching Frequency should just mean the switching frequency of the buck converter.

1. What is tolerance about switching frequency?
2. I measuerd them as close IC's IN and OUT pins. But Duty rate is differece. Why?
3. I know Max current limit is 100mA in datasheet. But I want to caculate max current Limit in upper case. Please let me know how to caculate this or if you have some document about this, pls send to me.
4. As I know TPS62736's switching frequency is 2MHz. but In upper graph, unit is KHz. What is major Switching Frequency? Please let me know detail.

Regarding 1, it is hysteretic not PWM fixed frequency so it will varying.  The maximum is around 2MHz but we don’t have a min/max.

Regarding 2, please measure the IC's IN and OUT saparately and then do the calcualtion to check if the frequency mathes the what shown on the scope.

Regarding 3, it is buck converter running in hysteretic DCM.   Power balance eff=Po/Pi=Vo*Io/(Vin*Iinavg) where Inavg = 50% * Iswpk when DCM converter is running at boundary of CCM.  Best to use the datasheet figures that plot Max Iout vs Vin for different Vout levels.

Regarding 4, the “major” switching frequency is the frequeny of the output ripple which is the same as the time between groups/bursts of the up to 2MHz switching pulses.

 

Thank you for your help, Jing Zou.