TPS61391: About MONIN pin and Ilim setting

Hello teritama,

The expert for this device is out of the office until beginning of next week. Please expect a detailed answer 

The output voltage level is about 10 times as high as the input voltage, please check the maximum duty cycle of the TPS61391 by using the quickstart calculator: SLVC801 Calculation tool | TI.com

Only if the maximum necessary duty cycle is below the maximum duty cycle available on the device, you will get the voltage you want to have.

Best regards,
Brigitte

Hi teritama,

If the output short protection is needed, then please connect MONIN pin to VOUT through filter(Rfiltor and Cfiltor) for current monitor.

The inductor calculation is not correct. I think it may be caused by wrong unit. Please refer to the Calculator that Brigitte provided. With that calculator, you will get the min, max and recommended inductor of 4.7μH.

Regards

Lei 

Hi Lei-san, Brigitte-san,

Thank you for reply. 

In my understanding, Ishort pin is used to setting the threshold of APD currnet not VOUT. When connect MONIN to VOUT, does current limit(typ 1000mA) enable as VOUT short current protection?

In our case, is this setting value not concerned the device operation? 

I calculated by attached tool, the result is below. L_max and L_min shows over 4.7uH, but L_recommend is 4.7uF.

does it mean, should we use 4.7uF at first?

Best regards,

teritama

Hi teritama,

In the calculation tool, the current limit (cell C15) is 0.8A, not 0.1A. After this value is modified, you will get the correct L_recommend.

Here is an update: in previous calculation, I used the max Iout as 6mA. If it is 14mA, based on the following formula, the recommended inductor is 6.8μH. 

In the calculation tool, the efficiency is not considered in the L_min, which should be added. So the 4.7μH L_min calculated from the tool will be smaller than the needed one.

The ISHORT pin is used to set the max current that flows through VOUT --> MONIN --> APD.

When use APD as a output port, the short protection will take effect when APD is shorted.

No problem to set ISHORT to have max 20mA current that flows through VOUT --> MONIN --> APD. It's close to the max Iout limited by the current limit(typ 1000mA).

If use VOUT as the output port and it is shorted, no matter how the ISHORT set, there will be no short protection. And in this condition of VOUT shorted to GND, current limit(typ 1000mA) takes no effect. Since no matter the low side FET is on or off, the indictor current will increase.

Regards

Lei 

Hi Lei-san,

Thank you for reply.

I understood my miss understanding about current limit. 

>No problem to set ISHORT to have max 20mA current that flows through VOUT --> MONIN --> APD. It's close to the max Iout limited by the current limit(typ 1000mA).

⇒In my understanding MONIN and ISHORT is for protection of APD output. If we don't need APD output, what terminal treatment of these pin is recommended?

　Is it no problem these pin connect to GND?

Best regards,

teritama

Hi teritama,

If you use the boost function only, then all the pins of the AVCC, CAP, APD, MONIN, MON1 and MON2 can be open.

Or just make the two input pins of AVCC and MONIN connected to GND, and leave the pins of CAP, APD, MON1 and MON2 open.

Regards

Lei