LM60430-Q1: Output Capacitor

Hi Donghyun,

Thanks for reaching out!

You can try simulating the device on WEBENCH and change the passives based on what you plan on using and your operating conditions.

The values recommended in the table are only typical and the device can operate with different passive combinations based on the output voltage, input voltage range, transient requirements (load and line), etc. 

Any reason why you are using a 3A rated device for an application that only requires 1A of current?

Thanks,

Best Regards,

Taru

Currently, due to a request from our customer, we need to obtain confirmation from TI regarding our output capacitor configuration.

In our application, the input voltage range for the LM60430-Q1 is 9–16V, and the output voltage is 5V. This 5V output is used as the input voltage for TI’s PMIC LP87524J-Q1. As mentioned previously, the maximum load current is 720mA.

Given these conditions, we would like to request confirmation on whether using two 22uF output capacitors for the LM60430-Q1 would be acceptable without any issues.

Thank you for your support.

Hello,

We are currently using the LM60430-Q1 in our design, and there are specific reasons why we are strongly committed to this device.

The EMI performance of the LM60430-Q1 is excellent, and its low dropout voltage is highly beneficial for our application. Most importantly, we have already passed EMC testing with this regulator, so switching to a different device would require significant design changes and retesting, which is not a trivial decision for us.

Given this context, we would like to ask for your support in confirming a key design parameter:

Under the following conditions:

• Input voltage: 9–16 V

• Output voltage: 5 V

• Maximum load current: 750 mA

• Maximum allowable output voltage deviation (ΔVOUT): 300 mV

Could you please confirm the minimum required output capacitance to ensure stable operation and acceptable transient response?

We are trying to minimize the output capacitor value because our PCB space is very limited.

We would really appreciate your help in confirming this value so that we can evaluate whether any further design trade-offs or regulator changes are necessary.

Thank you very much for your support.

Best regards

Hello,

The output of this regulator is used as the input to a PMIC (LP87524J), and there are four 10uF capacitors connected in parallel at the PMIC input.
Would it be possible for these PMIC input capacitors to compensate for the insufficient output capacitance of the LM60430-Q1?

If layout distance is a critical factor, could you advise how close the regulator output and the PMIC input should be placed (in millimeters)?

Looking forward to your response.
Thank you.

Hi Donghyun,

Apologies for the delay - I was out of office for the past week or so. 

if I understand correctly, 

You are asking if the Buck and PMIC in the above picture are close enough - can you consider the input cap of the PMIC as part of the output capacitance of the buck? Right? 

Thanks,

Best Regards,

Taru

Yes, that's correct. I'm asking how close the Buck and the PMIC need to be in order for the input capacitors of the PMIC to be considered as part of the output capacitance of the Buck regulator.

Hi Donghyun,

Theoretically speaking - this can work.

However, it is very difficult to say if this will work in practice. It depends on your PCB routing and power delivery network - this will require you to model your PCB parasitic inductance and capacitance - which will determine how your transfer function will look like and if the PMIC input capacitance can 'add' to the DC/DC output capacitance. 

You can check if the load transient response is according to your expectations - If yes, you can go ahead with the current implementation as well. 

The best way here is to place 2x 100uF as suggested earlier which should take up almost the same amount of space as 2x 22uF. 

Thanks,

Best Regards,

Taru