TPS2421-2: Current value in retry mode

Ruben Rodrigues73

Part Number: TPS2421-2
Other Parts Discussed in Thread: TPS2595

Hi,

I'm testing TPS2421 and i think that is working correctly. I tested Current Set, and TPS cuts at 2.85A, with RSET = 66k5 which means that my load is about 3R70. After this i increase the Load resistance and TPS just restarts at 1,80A which means 7R load resistance. From calculations that i send attached i see that resistive load at startup should be more than 12R, this is related to this or not?

Why TPS don't start after current is below ISET or why needs 12R at startup? In real environment is not possible remove the load at startup...

Best Regards1781.TPS2421_Design_Tool_Rev-.xls

over 6 years ago

0 Rakesh over 6 years ago

TI__Guru* 95791 points

Hi Ruben,

I will look into this and get back you soon.

Best regards
Rakesh

0 Rakesh over 6 years ago in reply to Rakesh

TI__Guru* 95791 points

Hi Ruben,

The TPS2421 device has internal constant power engine of 5W (typ) to ensure FET SOA during startup. This puts a limitation on the minimum load resistance with which we can achieve successful startup.

Can you please let us know the system requirements to suggest a suitable part? Are you already using this device in any specific project? what is the end-equipment and application use case?

Best regards
Rakesh

0 Ruben Rodrigues73 over 6 years ago in reply to Rakesh

Intellectual 405 points

Hi Rakesh,

This means that we can have 20v and 5A like you said in datasheet. For example at 12v, we just can have a load of 0.4A.

In my application we can use it for different thinks, voltages like 5v and 12v and loads with operating currents like 3.5A, 2.5A, 1.6A..

Don't works for this right?

Thanks

0 Ruben Rodrigues73 over 6 years ago in reply to Rakesh

Intellectual 405 points

If just gives 5W how you explain that i get 2.7A at startup with 5V? This configuration gives 13.5W...

0 Rakesh over 6 years ago in reply to Ruben Rodrigues73

TI__Guru* 95791 points

Hi Ruben,

For your 5V system testing, I assume you are using resistance of 5V/2.7A =1.85Ohm. Capture power dissipation (like figure 21 in the datasheet) in this test case. I believe the device is operating <5W power limit during startup which is helping for successful startup.

I would recommend to use TPS2595 device www.ti.com/.../description for your 5V/12V applications and to support 3.5A, 2.5A, 1.6A currents. It is compact in size and offers better current limit accuracy.

Best regards
Rakesh

0 Ruben Rodrigues73 over 6 years ago in reply to Rakesh

Intellectual 405 points

Hi,

The package of TPS2595 isn't good for us.. By the way, i don't think that device is operating <5W power limit since P = 5*2.7 = 13.5W. TPS2595 should have same Power limit, or not?

Thanks

0 Rakesh over 6 years ago in reply to Ruben Rodrigues73

TI__Guru* 95791 points

Hi Ruben,

What is the end-equipment? Is it for industrial market?
TPS2595 does not have power limit function.

Best regards,
Rakesh

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TPS2421-2: Current value in retry mode