TPS62A02: question

Hi Koji-san,

1) The output ripple formula explanation could be found in the following app notes:

https://www.ti.com/lit/an/slva477b/slva477b.pdf?ts=1689324586521&ref_url=https%253A%252F%252Fwww.google.com%252F

https://www.ti.com/lit/an/slva057/slva057.pdf?ts=1689324588033&ref_url=https%253A%252F%252Fwww.google.com%252F

2) I would recommend to follow the datasheet recommendations of 1uH or 0.47uH. This is because the device has been validated and tested to give its optimal performance within its recommended operating conditions. We cannot guarantee or confirm the device performance outside of datasheet specs.

3) I checked our validation data and the PSM to PWM transition happens around 200mA. The PWM to PSM and vice versa transition happens depending on the load current. As the load current decreases below the threshold value, the switching frequency drops and the device enters the PSM mode to maintain high efficiency. 

Thanks and let me know in something is unclear.

Best regards

Sneha 

Sneha-san,

Thank you for your support.

1) which equation in application note shows the output voltage ripple calculation?

2) I think that 0.47uH is TYP value on catalog inductor. Could you tell me min inductance value for TPS62A02 stability when they use TYP 0.47uH? 

3) What does 200mA mean? Does bottom inductor current reach to 200mA, then, enter power save mode? What condition from power save mode to FPWM mode?

Thanks,

Koji Ikeda

Hi Koji-san, 

-- You can estimate the output ripple using this:

-- +/-20% tolerance can be considered while choosing the inductor. All the device characterization considers this tolerance limit. Hence, within this range, I don't think there should be any problem.

-- As I mentioned above, the PSM to PWM transition is load current dependant. So, 200mA is the load current for the device. So the PFM to PWM and PWM to PSM transition happens around the same threshold value. 

Thanks!

Best regards

Sneha 

Sneha-san,

Thank you for your support. 

>-- As I mentioned above, the PSM to PWM transition is load current dependant. So, 200mA is the load current for the device. So the PFM to PWM and PWM to PSM transition happens around the same threshold value. 

Please let me confirm, does TPS62A02 monitor DC load current and when the load current goes below 200mA, then, enter PFM mode? Is the 200mA threshold no dependency by input, output and external components?

I assume that zero current detect on block diagram would be used for this transition... 

Thanks,

Koji Ikeda

Hi Koji-san,

Apologize if I was not clear before. I mentioned that the data of 200mA load current is based on the validation data, which is measured on one unit. 

Therefore, I provided you this information as a reference value. This means it is expected that the threshold to be around 200mA. Ofcourse, it may slightly vary dependant on the input, output and L and C tolerances. However, I do not expect much variation from this value. I would suggest for customer to verify it on their application circuit with their operating conditions if it is very critical for them. 

I hope this helps.

Best regards

Sneha 

Sneha-san,

They will evaluate this transition point/threshold from PWM to PSM and from PSM to PWM. But, they ask TPS62A02 internal circuit behavior, to investigate logically..... Could you support their inquiry?

Thanks,

Koji Ikeda

Hi Koji-san,

Could you please elaborate what internal circuit behaviour they would like to understand?

Best regards

Sneha

Sneha-san,

They don't need detailed internal circuit, but, they need to know how TPS62A02 move transition from PWM to PSM and from PSM to PWM and the threshold. Could you support? I feel that IOUT 200mA would be a reference under an usage setup.

I think that general DCDC has zero current detect on low side and if detected, enter from PWM to PSM or PSM to PWM. Does TPS62A02 use different method?

Thanks,

Koji Ikeda

Hi koji-san,

Okay. Yes, you are correct. There is a low side zero detect circuit which detects the inductor current reaching zero and then the pwm generator skips the pulses, hence entering the pfm mode. 

Best regards

Sneha 

Sneha-san,

Thank you for your support. Could you show low side zero current threshold?

Thanks,
Koji Ikeda

Hi Koji-san,

What do you mean by low side zero current threshold? 

The internal circuit detects the zero crossing of the inductor current, which depends on the load current and the slope of the inductor current. 

Overall, the PFM-PWM threshold is mainly dependant on load current. Also, I would expect it to slightly vary with Vin and Vout. 

200mA is based on the test data at Vin-5V and Vout 1.8V.

Best regards

Sneha