Where is the current going?

Thread Starter

carto

Joined Feb 3, 2014
45
Hi, I am using the linear voltage regulator BA00BC0WCP-V5E2 to convert 12 V to 7.5 V. The datasheet (https://www.rohm.com/products/power...e-output-ldo-regulators/ba00cc0wcp-v5-product) lists a "Shutdown circuit current" of 10 uA. But when I use the regulator as shown in the attached schematic, with no power to the regulator's "CTL" pin, I measure a current of 2.5 mA at the fuse (labeled "U2"). I measured this by pulling out the fuse and putting one probe at the "1" spot on the fuse schematic and the other probe at the "2" spot.
I am a beginner at this and don't know whether I am misinterpreting the datasheet, incorrectly measuring the current, or have misplaced the 0.33 uF capacitor or some other component. I chose the capacitor from information on the datasheet. I am hoping to have the 12 V current tiny when the regulator is shut off.
Can anyone help? Thank you!

Leaking current.jpg
 

panic mode

Joined Oct 10, 2011
2,110
i see no fuse F2, so i guess you mean U? is the "fuse"?

anyway, datasheet shows that expected bias current is 2.5mA and it can be as much as 5mA.
so your measurements confirm that device is operating within specs. the question is what is the voltage at CTL input?
are you pulling it low to less than 0.8V? i hope you are not just letting it float...(do not leave it open)
 
Last edited:

BobTPH

Joined Jun 5, 2013
4,742
You also violated the guidance for the feedback resistors. The datasheet calls for your R8 to be between 2K snd 15K.

Bob
 

Thread Starter

carto

Joined Feb 3, 2014
45
First of all, I apologize: I posted the wrong link for the BA00BC0WCP-V5E2. Here is the correct page (with a datasheet button) for that: https://www.rohm.com/products/power...e-output-ldo-regulators/ba00bc0wcp-v5-product . I think the resistor I used works for that datasheet.

The values for the current and the voltage at the control pin seem to vary among measurements and times. Right now, I measure a current of 1.4 mA from the 12 V source while the voltage at the CTL pin of the regulator is 0.1 mV.

I do have a pulldown resistor at on the CTL line.

I have been confused by the differences between "quiescent current" and "shutdown circuit current". Apparently now I should learn about bias current too.

Thank you, and sorry again about leading you to the wrong datasheet.
 

Thread Starter

carto

Joined Feb 3, 2014
45
I checked again. When the voltage at the CTL pin of the regulator is 0.1 mV (so the regulator is "off"), the current from the 12 V battery (to the regulator's "VCC" pin, as measured at the fuse holder "U2") is 1.14 mA. When the voltage at CTL is 4.2 V (the regulator is on), the current is 2.5 V. I was expecting that when the regulator was "off", the current I'd see would be the "Shutdown circuit current". On the datasheet, this is listed as 0 uA Typical and 10 uA Maximum (with "Conditions VCTL = 0 V while in OFF mode"). I do see a "Bias current" listed as 0.5-0.9 mA (Conditions IO = 0 mA). Do I need to add this to the Shutdown Current to find the expected current when the regulator is in the off state? I am not finding this info clearly stated so far. Thank you!
 

Thread Starter

carto

Joined Feb 3, 2014
45
Maybe this will help another beginner: I found out where the current was going. I thought I'd done a good job soldering the components onto the circuit board, but when I looked with a magnifier, I found that there was some solder debris between two of the through-hole pins. Since I cleared this away I have been getting between 1.5 and 5.5 uA for the 12 V current when there is 0 V at the CTL pin. The datasheet lists 0-10 uA as the "Shutdown circuit current"--so it seems all is well now.
 
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