LMR54406: Can't get the specified current value with LMR54406

Hi,

Test on breadboard may bring noise as the DCDC converter should be layout optimized. Maybe can you get an EVM for test? Or can you make a PCB board to test?

Regards,

Hongjia

Mr.Hongjia,

Thank you for sending me your advice.

I understand that you have to optimize the layout for testing.

Also,I understand that noise is generated, but is it possible that the specified current cannot be obtained when testing using a breadboard?

I would like to know what is the main cause. Also, I would like to know the impotant points when selecting peripheral parts such as C,R,L.

Best Regards,

Masaki Noguchi

NEMOTO & Co.,Ltd

Hi,

As LMR54406 is switching with high 1.1MHz frequency and the breadboard usually has large parasitic, there will be large noise which is very possible to make the circuit misfunction. I would strongly recommend test on PCB. 

Regarding the peripheral parts, please put the input capacitor near the IC. And the value of L can be smaller such as 4.7uH. Cout=22uF looks good. For the detailed selection considerations for each component, you can refer to Datasheet Section 9.2.2 Detailed Design Consideration for more details. 

Regards,

Hongjia

Dear Mr.Hongjia

Thank you for your advice, this is Noguchi from Nemoto & Co.,Ltd.

Do you sell an evaluation board for the LMR54406? If you sell it, please let me know the part number.

Also, this device seems to have a strict design, so I would like to consider alternatives. As for the specs, I would like to generate 5V input, 2.5V output, and 500mA. I would also like a device that is resistant to lightning surges.

Best Regards,

Hi Noguchi,

We have LMR54410 EVM. I have put the link below and you can order online. LMR54410 is 1A version and it is P2P with LMR54406. Layout should be paid attention to for all the DCDCs, not only for this device. As your input voltage is low, I will also loop in our colleague from the Low Vin buck team and they will give you the other proposal for your application. 

https://www.ti.com/tool/LMR54410EVM

Regards,

Hongjia

Hi Noguchi,

You could consider the following low VIN devices for this application: TPS62824, TPS628510/1

Best regards,

Varun

Dear Mr.varun,

Thank you for your advice. Can this device generate an output voltage of 2.5V, 500mA from an input voltage of 5V? Also, is it easy to evaluate? It would be helpful if you could send me the datasheet.

Best Regards,

Masaki Noguchi

NEMOTO & Co.,Ltd

Dear Mr. Noguchi,

Yes both devices can generate 2.5V output with 500mA from a 5V supply. 

These are the links for the datasheets and EVMs to evaluate them:

• TPS62824: Datasheet https://www.ti.com/lit/ds/symlink/tps62824.pdf EVM: https://www.ti.com/tool/TPS62825EVM-794 (only EVM of 2A version is available)
• TPS628511: Datasheet https://www.ti.com/lit/ds/symlink/tps628511.pdf EVM: https://www.ti.com/tool/TPS628511EVM-139

Best regards,

Varun         

Dear Mr.Varan,

Thank you for your reply quickly.

We will order these device you recommend.

Are these devices easier to evaluate than LMR54406?

 I have heard that it is difficult to evaluate device LMR54406 on a general-purpose board due to its high switching frequency. Is it possible to evaluate the device you introduced on a general-purpose board?

Best Regards,

Masaki Noguchi

Dear Mr. Noguchi,

I am not sure if you will be able to get it to work on a bread board. You will need to design a PCB or use the EVM to evaluate it.

Best regards,

Varun

Dear Mr.Varun,

We are you expecting the following items for  device .

1. Input 5V power supply, output 2.5V, 500mA (usually about 200mA)
2. Even if the above current is applied, the device should generate little heat.
3. The same operation is possible even in an environment with an ambient temperature of 50 degrees.
4. Able to withstand lightning surge 4kv

As for 4, the device is tolerant, and we are planning to add a varistor and test it.

Which device best meets this requirement?

Best Regards,

Masaki Noguchi

Dear Mr Noguchi,

The 2 devices I recommended should be able to meet points 1-3 on a PCB.

Our devices don't usually have lightening surge protection. There is built in ESD protection that has been tested according to JEDEC standards. The lightening surge probably has a different voltage-time profile compared to an ESD strike.

Adding extra protection diodes for the lightening surge may be a possible solution.

Best regards,

Varun

Dear Mr.Varun,

Thank you for your comments and advice.

Could you tell me reference circuit diagram( using diodes) for the lightening surge?

Best Regards,

Masaki Noguchi

Dear Mr. Noguchi,

You would have to connect the diode between the rail with the surge and GND plane.

You can refer to this app note for more information: https://www.ti.com/lit/an/slvae37/slvae37.pdf

Best regards,

Varun

Dear Mr.Varun,

Thank you for your advice for lightning surge countermeasures.

If you know the device name that is effective or commonly used to protect the switching power supply device you are selecting , please let me know.

Best Regards,

Masaki Noguchi

Dear Mr. Noguchi,

Could you make a new e2e post for recommendations for TVS devices for lightening surges? This would help tag the right team to support you with the protection diodes.

Best regards,

Varun

Dear Mr,Varun,

Thank you for your reply.

I will make a new e2e post for for recommendations for TVS devices for lightening surges.

By the way,

Already orderd several devices you recommended. 

How much heat do you think the device itself generates when the input voltage is 5V, the output voltage is 2.5V, and 500mA?

Best Regards,

Masaki Noguchi