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TPS61041 pulls excessive current

William Sell
Prodigy 120 points
Other Parts Discussed in Thread: TPS61041

Trying to get the LCD back light circuit running, but cannot even get the board passed a 1 volt on the input as the current pull is so high.  The circuit is from the TI spec (where EN is driven by PWM to control brightness), and is laid out correctly;  Not sure how to proceed here.  The TPS61041 pulls current regardless of whether the led string is connected or not.  We are looking to take 6VDC to 18VDC.  The inductor is 10uH, charge cap is 22uF.  The limit resistor is 82ohms.  Given the circuit has been correctly lifted from the TI spec, what could possibly cause this device to draw excessive current?   Right now, I have the inductor removed so I am able to debug the rest of the board...any ideas??

thanks

-Bill

 

 

  • 0
    TI__Guru**** 166096 points

    Use an ohmmeter to ohm the resistance to ground on VIN, EN, SW and FB.  If not high impedance then either the board has a short or the IC is damaged.  Note that if you turned on the IC without the LED load at any time, the control loop is open and the SW pin will over voltage and likely be damaged.  You would need to add some sort of over voltage protection circuit like a diode from the output to FB pin as shown in http://www.ti.com/litv/pdf/slva227

     

  • 0 in reply to Jeff F
    Prodigy 120 points

    Boy, some times things are too frustrating.  So the problem is there are two part types; the DRV and the DBV.  The layout guy used the pins for the DBV and the part which was stuffed was the DRV.  So instead of pin 1 being SW it is gnd so we pass Vin directly to GND through the inductor...grrr!

     

    -Bill