How to Achieve 1.2V 3A Output from LTM4623 with 5V Input and 0.5A Input Current Limit?

Hello all,
I have to design 3 DC/DC converters for a FPGA board with 3 needed voltages,
1.2 V, 1.8V and 3.3 V with 5 volts input. I have selected LTM4623.

What bothers me about the LTM4623 is that it is limited to 0.5A input current.

This means that certain output currents are not possible at all. Could you please help me, how can come out with 5 V input voltage and 0,5A input current e.g. 1,2V output with 3 A output current?

Thank you very much
best regards
Somayeh

There won't be an input current limit, only output. It will be set by the power dissipation and current limit on the switches. The data sheet gives a typical input current for a specified output, but that will just be for a specified set of input and output conditions, and probably says more about the efficiency than anything else. The first three graphs on page 5 of the data sheet show output currents of three amps for 3 different input voltages. Page 10 also discusses Vin to Vout stepdown ratios. They also have the ability to track if connected together.
You will also need to do appropriate thermal design.
If this is the only chip that is ball grid, then it may be worth considering a different package, if the FPGA is ball grid, then no matter.
Cheers,
Richard

It is generally not possible to directly produce an output voltage of 1.2 V with a 5 V input using a DC/DC converter that is limited to a maximum input current of 0.5 A. The reason for this is that the output current is determined by the input current and the voltage conversion ratio of the converter.

For example, if you want to produce an output voltage of 1.2 V with a 5 V input and a DC/DC converter with a voltage conversion ratio of 1:2, the output current would be equal to the input current divided by the conversion ratio, or 0.5 A / 2 = 0.25 A. If you need an output current of 3 A, you would need an input current of 3 A * 2 = 6 A, which is not possible with the LTM4623.

One way to potentially meet your output current requirement would be to use multiple LTM4623 converters in parallel. This would allow you to increase the total output current by adding more converter units. However, this would also increase the input current requirements, so you would need to ensure that your power supply is capable of providing the necessary current.

Alternatively, you could consider using a different DC/DC converter that is capable of handling higher input currents. There are many different DC/DC converters available on the market with a wide range of current and voltage ratings, so you should be able to find a converter that meets your specific requirements.

It sounds like you are trying to use the LTM4623 as a standalone DC-DC converter to generate the three different output voltages that you need.

The LTM4623 has a maximum input current limit of 0.5A, which means that it cannot handle input currents that are higher than 0.5A. This can be a problem if you need to generate high output currents, as the input current will be proportionally higher.

One way to address this issue is to use multiple LTM4623 converters in parallel to increase the available input current. For example, if you need 3A of output current at 1.2V, you could use three LTM4623 converters in parallel, each with a 0.5A input current limit. This would allow you to generate a total of 1.5A of output current at 1.2V.

Another option is to use a different DC-DC converter with a higher input current limit. There are many different DC-DC converters available on the market, and some of them may have higher input current limits that would be suitable for your application.

It's important to note that you will need to carefully consider the power dissipation and thermal management of the DC-DC converter(s) that you choose. If you are generating high output currents, the converter(s) will need to be able to handle the resulting power dissipation without overheating.

I hope this helps! Let me know if you have any other questions.