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TPS92692: Current sense

Takashi Yamaguchi
Genius 13450 points
Part Number: TPS92692

Hi team,

Could you help with the question below from my customer?

How behave this device if the current detection can not be done correctly due to the CSP or CSN pin is open or short each other?
Customer is concerned that the feedback control may not work properly and excessive current may flow.

Regards,

Yamaguchi

  • 0
    TI__Mastermind 18890 points

    Hi Takashi-san,

    If the CSP pin or CSN if are shorted to each other or open then as you mentioned the loop will not sense any current feedback and will command for more current and excessive current will occur.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    TI__Genius 13450 points

    Hi Tuan-san,

    I received the additional questions about the excessive current when CSP pin or CSN are shorted to each other or open. Could you support the questions below?

    1. If the CSP pin or CSN are shorted to each other or open, will the excessive current flow until LED or FET is broken? Does the device have another protection to stop this excessive current?

    2. Is the Switch Current Limit function using RIS resistor able to limit the excessive current due to the CSP pin or CSN are shorted to each other or open? 

    3.If the excessive current flows when one side (CSP or CSN) of the internal current sense amplifier is open, could you explain the principle?

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Mastermind 18890 points

    Hi Yamaguchi-san,

    1.  If CSP and CSN are shorted together then the current in the LED will ramp up high if it's not damaged until the switch over current protection on IS is activated and the PWM.  you can read this in section section 8.3.7 (page 18) of the data sheet.

         If CSP and CSN are open the same as above with the shorted together will happen.

    2.  The switch current limit using RIS will be able to limit the excessive current if designed properly.  However, there will always be excessive current and this will depend of the design and whether it will protect the LED or not.

    3.  If only CSP is open then the current will ramp up excessively since CSP is pull down internally to ground and with CSN being high or ground externally the differential will sense as no current or low current and the loop will command higher current until the IS over current protection is activated.  Again, this is provided that the LED and FET can handle this over current. 

    If only CSN is open then CSN will be pull down internally with a high resistance to ground.  If the differential of CSP relative to ground is lower than the commanded current then the regulator will command current until this differential set point is reached.  If it's not reached then the IS over current will be activated.  If the differential is higher than the commanded current then the regulator will never turn on at all since it's sensing over current on the LED already. 

    Thanks Tuan