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TPS62050 operational malfunction

Talini Pinto Jayawardena
Prodigy 80 points
Other Parts Discussed in Thread: TPS62050

Hi,

I'm trying to use a TPS62050 buck converter to obtain 3.4V from 8.3V. The pins are connected as given below:

1. Vin - 10uF (electrolytic) to ground; Power supply Vout connected to Vin

2. LBO - Grounded

3. GND - Connected to PGnd (pin 10)

4. PG - Grounded

5. FB - R1 (580kohm) connected between pin5 (FB) and pin9(SW); two resistors were used to make up the resistor value, with a trace of ~5cm between the resistors; R2 (100kohm) connected between FB and GND.

6. LBI - Grounded

7. SYNC - Connected to Vin (required in forced PWM mode)

8. EN - Connected to 5V/Gnd, based on when the device needs to be switched on.

9. SW - Connected to 22uH inductor; R1(580kohm) between SW and FB; 22uF between SW and PGND

10. PGND - Connected to GND

When the device is powered on and enabled with no load, ~100mA is drawn and it gets very hot. Output is not steady, with significant rippling, and at 2.10V. When a load of 6.8ohm (to give 500mA), the voltage drops to 1.70V. Please note that we need to operate in forced PWM mode, and operate a device that draws around 500mA.

Any help will be very much appreciated!

Thank you.

 

Talini

 

  • 0
    TI__Guru**** 150650 points

    The only part that should be connected to SW is the inductor.  The output capacitor and feedback resistors need to be connected to Vout.  Look at any of the schematics in the datasheet for the proper wiring.

    Also, we highly recommend that you test your circuit on the EVM instead of making your own PCB.  Layout is very important for these parts and bad layout can cause the part not to work.

    Also, your input cap should really be a ceramic for the low impedance needed by the IC.

  • 0 in reply to Chris Glaser
    Prodigy 80 points

    Hi,

    Thank you for your reply. I made an error in describing my pin out:

    Pin 9. Only the inductor is connected to SW. The resistors and capacitors are connected to the other end of the inductor - essentially Vout.

    I will replace the electrolytic capacitor with a ceramic one. Should this have such a significant effect as to prevent the device from working?

    Also, is it normal for the device to draw ~100mA with no load, and for it to heat up?

     

    Thanks,

    Talini

  • 0 in reply to Talini Pinto Jayawardena
    TI__Guru**** 150650 points

    Yes, using a high impedance input cap can cause bad operation and it could damage the IC.

    No, the IC should not draw 100 mA at no load.  You may have damaged it.

    Could you post your board layout?  We strongly recommend that you start testing your circuits on the EVM with its good layout.