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TPS55288: It cannot output over 2.5A even 5A current limitation

koji hirosawa
Prodigy 70 points
Part Number: TPS55288


Hi,

I am trying to use TPS55288 for Power delivery 5V/9V/15V/20V, i set current limitation is 5A.

But when over 2.5A loading in all voltage setting, its output voltage was drop down.

I suppose some protection was occurred.

I2C setting is below, and circuit diagram is attached.

Please advice what i should change for 5A current.

[I2C setting in case 20V output]

Register Address Register Name 20V output Meaning
0h VREF [7:0] 0xC0 1129mV
1h VREF [9:8] 0x03
2h Current Limit 0xE4 50mV/10mΩ = 5A
3h Slew Rate 0x01 Default
4h Feedback Selection 0x03 Internal FB, FB ratio to 0.0564
5h Cable Compensation 0xE0  Default
6h Mode 0xA4  Output enable, 0x75h,

[Circuit Diagram]

Regards,

Hirosawa

  • 0
    TI__Mastermind 34231 points

    Hi Hirosawa,

    Thank you for reaching out on E2E.

    May I know the application Vin range? Could you also share the layout? The layout is very important for a DC/DC converter. An improper layout will cause device abnormal behaviors.

  • 0 in reply to Zack Liu
    Prodigy 70 points

    Hi Zack,

    Vin range is 19V~35V. 

    Layout and Circuit diagram are attached.  (Previous circuit diagram is that Reference number is different version.) 

    Regards,

    Hirosawa

  • 0 in reply to koji hirosawa
    TI__Mastermind 34231 points

    Hi Hirosawa,

    The layout is poor. Please follow the TPS55288 layout guideline app note.

    The root cause should be the output current sense circuit is not routed properly. And it's needed to add a 100nF or 220nF ceramic capacitor close to ISP, ISN pin to filter the noise.

    For the schematic, suggest change R115 to 20kohm, C44 to 10nF, add one more 100pF ceramic capacitor across COMP pin and AGND pin.

  • 0 in reply to Zack Liu
    Prodigy 70 points

    Hi Zack,

    Thank you for your advice.

    I tried to add 100nF ceramic capacitor close to ISP, ISN pin, and R115=20k, C44=10nF and add 100pF ceramic capacitor. across COMP and AGND pin.

    (except modify ISN, ISP pattern)

    Result is that Maximum current is 3.5A in 5V, 9V and 15V output case. But 20V output case, maximum current is 2.6A.

    They becomes better, but not enough. My expectation is 5A in all cases.

    Please advice more.

    Regards,

    Hirosawa

  • 0 in reply to koji hirosawa
    TI__Mastermind 34231 points

    Hi Hirosawa,

    As I said, the root cause is the output current sense ISP, ISN trace layout is poor. You need to update the layout to fix this issue. 

    For current PCB, you can firstly disable the output current limit function in register 2h.

  • 0 in reply to Zack Liu
    Prodigy 70 points

    Hi Zack,

    I checked disable the output current limit function, result was below table.

    5V and 9V output case are over 5A which is expected value.

    But 15V and 20V output case, it cannot output 5A(See red letter). I suppose other protection or limitation is working.

    After this protection was working, it cannot recover voltage even no load.

    I should send I2C voltage setting again for recover voltage. It is different behavior with the current limitation.

    Do you think which protection/limitation is working?

    Output Voltage

    Maximum current

    Expectation

    In case 5A current limit

    In case disable the current limit

    5V

    5A

    2.9A --> Current limit

    Over 5A  --> No limit

    9V

    5A

    2.9A --> Current limit

    Over 5A --> No limit

    15V

    5A

    3.0A --> Current limit

    3.5A --> Other limit?

    20V

    5A

    2.6A --> Other limit?

    2.6A --> Other limit?

    > You need to update the layout to fix this issue. 

    I will check with new PCB later.

    Regards,

    Hirosawa

  • 0 in reply to koji hirosawa
    TI__Mastermind 34231 points

    Hi Hirosawa,

    Did you set the external power supply current limit high enough? For this 100W application, the external power supply should support 100W power.

    The other one current limit protection is ILIM resistor, you already set to the maximum.