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TPS62745: Not working properly in constant current source (Both in with load and without load conditions)

Aswin S Dharman
Prodigy 150 points
Part Number: TPS62745

Tool/software:

My board is working in 4-20mA current loop. So the board should turn on at 3.6mA(10V). But while connecting this part the input voltage at 3.6mA reduced to 4.4V.

I had several debugging processes still it shows the same. Initially by increasing the input capacitance by 47uF and it started working. But after several days all the boards were stopped working.

So today I did one more test disabling the regulator (Pull down the Enable pin) that time the voltage is fine at 3.6mA shown 10V.

So I tried enabling the IC by keeping it off during the powerup that time its worked but after some time the output voltage reduced to 0.5V from 3.3V, the input voltage also reduced from 10V to 4.4V.

So please help me to resolve the issue as soon as possible

  • 0
    Prodigy 150 points

    Hi Team, please respond to this as soon as possible. I am stuck in the bring up only because this issue caused by the regulator IC 

  • 0 in reply to Aswin S Dharman
    TI__Mastermind 21221 points

    Hi Aswin,

    Looks like the VCC don't have enough capacity to supply TPS62745.

    You can use a external source to verify it.

    Thanks,

    Colin

  • 0 in reply to Colin Chen
    Prodigy 150 points

    Without load also it is showing the same behavior

  • 0 in reply to Aswin S Dharman
    TI__Mastermind 21221 points

    嗨，Aswin，

    您可以使用外部电源为 TPS62745供电 并查看是否有相同的行为。 

    谢谢，

    科林

  • 0 in reply to Colin Chen
    Prodigy 150 points

    With lesser load also it is behaving the same. Actually, the load regulation is not happening properly. And I observed one more thing like if the capacitors already charged and if I provide enable later it is working, but also if I provide any load the input voltage will reduce to 4.45V. Please do a detailed check and let me know your comments as soon as possible.

    For further information please find the below bill of material

    Reference value PCB Footprint Package Manufacturer partnumber Manufacturer
    C92 22uF,25V 805 0805 CL21A226MAYNNNE Samsung Electro-Mechanics
    C93,C225,C226 10uF 805 0805 GRM21BR61C106KE15L Murata Electronics
    C96 47uF,16V 1210 1210 GRM32ER61C476ME15L Murata Electronics
    C222 2.2uF C0402_SFO 0402 GRM155C81C225KE11D Murata Electronics
    D89,D90 5.1V SM_2_SOD-123F_107X67_36H SOD-123FL-2 KDZVTFTR5.1B Rohm Semiconductor
    L18 4.7uH IND_4MM_SMD 1616 LQH44PH4R7MPRL Murata Electronics
    L19,L20 BLM18HE152SN1D SM_2_FB_0603_37H 603 BLM18HE152SN1D Murata Electronics
    Q13 SI2315BDS-T1-BE3 SM_3_MFET_SOT23_120X55_80H SOT-23-3 SI2315BDS-T1-BE3 Vishay Siliconix
    Q14 2N7002K-7 SOT23-3 SOT-23-3 2N7002K-7 Diodes Incorporated
    R91 1M R0603_IPC_SM_782A 603 RN73H1JTTD1004F100 KOA Speer Electronics, Inc.
    R92,R97,R138 0R sm_2_res_0402_16h 0402 CR0402-J/-000GLF Bourns Inc.
    R135 100K sm_2_res_0603_22h 603 RC0603FR-07100KL YAGEO
    R136 150K sm_2_res_0603_22h 603 RC0603FR-07150KL YAGEO
    R137 10R 805 0805 RC0805FR-0710RL YAGEO
    U23 TPS62745DSSR DSS0012A WSON-12 TPS62745DSSR Texas Instruments
    C94 10uF 805 0805 GRM21BR61C106KE15L Murata Electronics
    R14 0R sm_2_res_0402_16h 0402 CR0402-J/-000GLF Bourns Inc.
    R121 1M R0603_IPC_SM_782A 603 RN73H1JTTD1004F100 KOA Speer Electronics, Inc.
  • 0 in reply to Aswin S Dharman
    TI__Mastermind 21221 points

    Hi Aswin,

    Could you use the external source with enough capabilities to supply power to  TPS62745?

    Thanks,

    Colin

  • 0 in reply to Colin Chen
    Prodigy 150 points

    Hey please understand ok, My device need to be work in current source, the overall consumption also less (Within 3.7mA). So, it has to work on 4-20mA current loop. One thing I had recently observed is like a dip is occurring on the input while the soft start works.

    ...

  • 0 in reply to Aswin S Dharman
    TI__Mastermind 21221 points

    HI Aswin,

    Our device should work in voltage source and with enough current capabilities.

    What i know from your description is that input voltage would drop when device was enable.

    Below are two common cause, one is VCC don't have enough source capabilities to drive and another is there is welding issue which resulting in leakage current.

    Thanks,

    Colin

  • 0 in reply to Colin Chen
    Prodigy 150 points

    Itis not working in voltage source also, the input voltage is reducing, and gradually current increases and the regulator stops working. I had added one more 47uF on the input side. But still, it shows the same result. But sometimes it remains stable. So please do a detailed review of the shared schematics and let me know any possible way to improve the stability

  • 0 in reply to Aswin S Dharman
    TI__Mastermind 21221 points

    Hi Aswin,

    VIN_SW is the output of a switch connecting VIN with VIN_SW when EN_VIN_SW = High. In this condition, this pin shouldn't connecting to GND because  it can causing leakage current . Please make it float.

    Thanks,

    Colin