TPS56221: Problems with TPS56221

Max Vishnevskii

Prodigy 50 points

Part Number: TPS56221

Hi, Sorry for my bad English. I have some problems with TPS56221:

1) ILIM doesn't work, if i connect resistor 2.8 kOhm to pin 18; Vout -0V;

2) when TPS56221 is working, it very hot (near 80 degrees). I now, that consumption current is 1,5 A.

Vin +12 V

Vout +1.6 V

over 4 years ago

0 David_Daniels over 4 years ago

TI__Mastermind 18515 points

The schematic looks reasonable for 1.6V 20A design. Can you send an image of your pcb layout?

0 Max Vishnevskii over 4 years ago in reply to David_Daniels

Prodigy 50 points

0 David_Daniels over 4 years ago in reply to Max Vishnevskii

TI__Mastermind 18515 points

It looks like the ILIM resistor is connected to the device pin and VIN (Net325_2). The ilim resistor needs to connect to ground and the pin

0 Max Vishnevskii over 4 years ago in reply to David_Daniels

Prodigy 50 points

resistor ILIM connected to GND. ( Absolute maximum ratings on pin ILIM is 7V, and VIN is 12V. If ILIM was connected to VIN, TPS56221 would be broken)

I have four TPS56221 on my board, and the situation is the same of each( I can't understand why power dissipation is so high!( when i remove R ILIM)

0 David_Daniels over 4 years ago in reply to Max Vishnevskii

TI__Mastermind 18515 points

Are the 4x22uF input capacitors on the same side of the board as the IC?

The below pics is a recommended layout for the device.

The input capacitors are on the same side of board and make a connecting copper pour to GND and VIN pins.

I am not sure how many vias you have, but I see 4 near the input capacitor on GND in image.

But the ground is not a connecting pour on the same layer, it looks like it is connected using vias.

The VDD capacitor is via connected to the pin 20.

VIN, VDD and BP5 need to be a steady voltage during operation.

Can you take an oscilloscope plots of the VIN, SW, VDD and BP5 with and with RILIM installed.

0 Max Vishnevskii over 4 years ago in reply to David_Daniels

Prodigy 50 points

2ч22uF and 1uF capacitors on one side, and 2x22uF on the other

VIN

0 David_Daniels over 4 years ago in reply to Max Vishnevskii

TI__Mastermind 18515 points

The SW node appears that it is not switching with the 200us time division setting and has a 700mV voltage.

Is the Vout voltage equal to 700mV.

If you use a 2 to 4 us time division, do you see the SW node transitioning from 0V to 12V.

Can you also check the COMP pin and EN/SS voltage?

With RILIM not installed, does the SW node transition from 0V to 12V?

Could your load be pulling more output current than than the current limit setting with 2.8kOHm Rilim? causing the device to current limit and hiccup etc.

Without the RILIM installed the overcurrent is disabled and could be the reason for the high temperature

What is the part number for the output capacitors? The worksheet shows an esr of 1ohm which seems high.

Can you send you altium pcb files to me at ddaniels (at@) ti.com (remove the (at )

0 Max Vishnevskii over 4 years ago in reply to David_Daniels

Prodigy 50 points

I've found a solution to the problem with my design!!!

l've noticed, that in my board design, pin BOOT connected to SW, through capacitor and resistor after Inductor, but in TPS56221 datasheet pin boot connected to SW before inductor. I changed it. I installed a capacitor 220pF between FB and SW. So, i see, that VOUT -1.6V and case temperature is normal

Thank you for help!!!

0 David_Daniels over 4 years ago in reply to Max Vishnevskii

TI__Mastermind 18515 points

Great to hear it!

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TPS56221: Problems with TPS56221