Texas Instruments TPS63020EVM-487

Sounds like your input power supply is current limiting. Can you check it?

It also can be a weak power supply connection at the input. Both issues can be checked easily by measuring the supply voltage of the device directly across the input capacitor.

I don't recall the power supply model number; however, it is a variable bench-top power supply with independent control of Voltage and Current for variable outputs, two outputs channels rated at 3 amps each, channels can be configured independent or master/slave. I'm using an independent channel, have banana plugs on power supply connecting to the positive-J1 header pin/negative -J3 header pin, with 5 VDC. If I remove the 3.3 ohm resister the output voltage is at 3.3VDC. I purchased some more resistors (4 ohm, 5 ohm and 6 ohm) that I want to try as well.

Do I need to find the user manual to verify if it is current limiting mode? How do I verify this?

Many power supplies will fold back the voltage when the current limit is reached. Depends on your model. But with 2 V input, you should still get 3.3V output. That EVM is only rated for 1 A typical. 2.5 A max. You should be able to get 3A if you can maintain 5V input.

The current limit of the TPS63020 is in the range of 4A (datasheet, page 5). This means it can pull more current at the input than your power supply can deliver. During startup with the load connected the input current definitely will hit that level. There are examples in the datasheet on page 17.

If the connection to the power supply is weak the power available at the input of the device is lower since there is significant voltage drop across the connection. This makes it even more likely that the test setup with power supply and EVM is getting stuck in the startup phase. 

Interesting... It sounds like a connection problem at the input because the power supply specs denote that the power supply can deliver 3 amps, and I've connected a 3.3 ohm resister to J4 an J6 which I should only draw 1 amp @ 3.3VDC.

I'll try checking the wires and banana plugs at the power supply, and reply back with results.

Please forgive me, but I'm not an expert in this field, so I humbling state that I think you are asking me if the power supply is imposing an upper limit on the current that may be delivered to a load to protect the circuits generating the current from harmful effects. Is that correct? Also, I was able to run by the lab and find that we have a Tenma 72-7245 power supply, Output (CH1, CH2): Voltage 0-30V, Current 0-3A, Tracking Series Voltage 0-60V and Tracking Parallel Current 0-6A. The manual states that both power supplies are completely transistorized, well-regulated, constant voltage/constant current supplies that will provide full rated output voltage at the maximum output current or ckn be continuously adjusted throughout the output range. The power supply has a CV&CC Indicator: The CV light (green light) is on when the CH1 supply is in the constant voltage operation, or when both the CH1 and CH2 supplies are in the constant voltage operation in either series or parallel tracking mode. The CC light (red light) is on when the CH1 supply is in the constant current operation.

Regards

Hi,

I want to connect a current scope to the input and output of the TPS63020EVM-487. I have the following current probe available: Tektronic A622

PROBE TYPE
Measurement/Accessory Type: AC/DC Split Core
Signal Type: AC/DC
Required Termination: 1 MegOhm
 
PROBE
Probe Bandwidth: 100 kHz
DC Current: 100 A
Max RMS Current: 71 A
Peak Current: 100 A
Min Current: 10 mA
Probe Cable Length (meter): 2

Will this current probe be sufficient for measuring the current on the TPS63020EVM-487? I'm wondering if the probe bandwidth of 100Khz will be an issue...

Regards