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CSD95378BQ5M: sch review request

Part Number: CSD95378BQ5M
Other Parts Discussed in Thread: TPS40428

Hi teams,

We use TPS40428+CSD95378BQ5M in our product,now we met some problem,

1、Set 5V output, the result is 0.6V.

2、Set 3.3V output, the result is 2V.

3、Both PWM  have no waveform.

4、Both PG is low.

So pls review our sch,and give some recommendation on this issue.

v1n0_sch_TPS40428+CSD95378BQ5M_issue.pdf

  • Hi Sara, 

    The schematic looks fine to me. 

    What's the PWM pin voltage? Can you probe it?

    Also, can you check below items?

    1. check if TPS40428 BP5 and BP3 voltage is correct. Check if 5V for CSD95378 is correct. 

    2. CNTL1 and CNTL2 voltage should be high to turn on rail. Can you double check?

    3. check FLT1 and FLT2 voltage. If FLT pin is pulled low externally, the rail keep off. 

    4. Can you use TI Fusion to check if any fault is reported by PMBus

    5. Check FB1 and FB2 voltage. 

    Thanks

    Qian

  • Hi Qin:

        the PWM pin voltage is both 1.5V high, and there is no PWM waveform.

       Items checking list below:

       1. TP40428 BP5 is 5V and BP3 is 3.3V

       2. CNTL1 is 2.4V  and CNTL2 is 3.3V (both pulled up to BP3, at the same time connect to CPLD which isn't programmed)

       3. FLT1 ahn FLT2 are both 0.365V, looks like something wrong happened.

       4.Because I don't have a TI USB Adapter and  firmware support, so I can't analyze the fault information through TI Fusion.

       5. FB1 and FB2 voltage  is both 0.367V,they didn't reach 600mV

    There are some additional questions below:

    6.  These chips were bought from market , so all setting are factory default value. Do we need to program previously?

    7. Smart mode has any effect on it?

    8. Is there any other ways to debug this power without TI Fusion?

    9. Which USB Adapter type is needed? And where I can borrow it or buy it?

    BR

    Yanfang Lin

  • Hi Yanfang, 

    5. Is FLT pin connected to other external circuit except the pull-up resistor? If it is, can you disconnect FLT pin from external circuit. If FLT pin is pulled low externally, the rail is not able to turn on. 

    6. The default setting should be fine.

    7. The part is in smart power mode in default. It is fine. 

    8. Did you check 5V (VRS_VDD5) for power stage? Can you also check the voltage between TAO pin and ground, and the voltage between CSP and CSN. Just want to check if there is anything wrong on power stage side. 

    9.  The USB adapter is at below link.

    http://www.ti.com/tool/USB-TO-GPIO?keyMatch=USB%20INTERFACE%20ADAPTER&tisearch=Search-EN-everything&usecase=part-number

    Thanks

    Qian

  • 5. No external circuit connect to the FLT pin except the pull-up resistor;

    6. VRS_VDD5  measure result is 5V;

        VDD33_TDO is 0V and VDD5_TDO<3.3V;

        VDD33_CS_DP/DN are both 1.226V and VDD5_CS_DP/DN are both 1.22V

         Is anything wrong here ? what else can I do? Looking for your reply, thanks ~

        BR

        Yanfang

  • Hi Yanfang, 

    At room temperature, TAO pin voltage should be around 0.6V. 

    It is abnormal if VDD5_TAO pin is 3.3V. 

    Can you use oscilloscope probe to check if PWM switch for a short time (default soft start time is 2.7ms) when EN pin is pulled from low to high?

    Thanks

    Qian

  • Yanfang, 

    The schematic shows 5V for power stage is converted from 12V. 

    Can you also check the power on sequence? 

    5V for power stage must be ready before TPS40428 switching is enabled. 

    Thanks

    Qian

  • Hi Qian: 

    As your suggestion, I've checked the Fault pins again ,and  found they have connected to CPLD which wasn't programmed. 

    there is a tip mentioned in  CPLD manual :"The default configuration of the I/O pins in a blank device is tri-state with a weak pulldown

    to GND." .This is why the fault pins were pulled low to 0.365V, I disconnected it to CPLD or set this pin as input , output voltage is normal now .

    Thanks a lot !

    I have monitored system through TI fusion, but I can't find the OV/OC ect. setting, where can I find them? What is the default factory setting?I wonder if I need to change the settings, thanks~ 

    BR

    Yanfang

  • Hi Yanfang, 

    Good to know the problem was solved. 

    Below is the screen shot of TPS40428 Fusion. The OC and OV setting is in red frame.