UCC2813-0: VCC Current way above limit for safe operation

Hi,

What is Vcc voltage in your design?

I am measuring:

• Max = 9.5V
• RMS = 7.57V

Also these measurements are all taken with a 1A load applied to the 12V output. 

Hi,

What is Vb voltage?

~160V rms, 170V peak 

Hi,

Please describe and show in your circuit where you cut the trace and how did you measure the current into the VCC pin.

I cut the trace where the red x is, and attached a wire to to the VCC pin and then the top of C405 and used a current probe with an oscilloscope to take the measurement. 

Hi,

I suspect your measuring approach causing high current. To verify, can you remove that wire and add a resistor at red x. You need try several resistor values, R= 20-ohm, 50-ohm, and 100-ohm. With a resistor in place, measure the dc voltage at VCC pin to GND pin, V1, and measure the dc voltage C405 to GND pin, V2. Then calculate the current I = (V2-V1)/R, then let me know what the current value from your test and calculations.

The current into VCC pin is specified as DC. So please find the DC current from the above test. We go from there.

Hi,

Actually, please follow the below to get the DC current I = (V2-V1)/R, R takes 20, 50, and 100 ohm.  

I will work to get the DC Current. Why does the resistor location matter though? 

Hi,

The location I show is to help get the dc current with spikes filtered out. The specs are for dc voltage and current.

Okay, here are the results when I used a scope to measure the voltages. 

With 20R: 

I_VCC = 16mA (max)

With 51R: 

I_VCC = 1.6mA (max)

With 110R: 

I_VCC = 0.4mA (max) 

So it seems like my current probe might have been my problem. 

Now, what about the high voltage I am measuring on the CS pin of the IC? Additionally, the voltage at the Source pin of the MOSFET is also higher than 1V. What can I do to decrease those values?