continuity testing

[tamethetikbalang]

Hello everyone,

I'm trying to measure the circuit protection diode of a certain pin, the problem is I have a bypass capacitor connected. Unfortunately, there is no way to disconnect that cap. I can measure ~0.5V, but I need a high settling time prior measurement. Is there a way to speed up my testing? Thanks in advance.

 

[tamethetikbalang]

Just to add, I'm forcing 10uA from ATE and measuring it using its voltmeter (FIMV).

 

[geekEE]

Is that truly a constant 10uA current or is it a constant voltage with a maximum of 10uA? If it's constant current, the voltage across the cap will be proportional to the current. If it's constant voltage, then it'll follow a e^(t/RC) curve. Either way, if you can increase the current, the capacitor voltage will change faster. Just don't exceed the voltage or current limits that the pin can handle.

Glenn

 

[geekEE]

Oops. I meant e^(-t/RC). Capacitor equations here:

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/capdis.html

Glenn

 

[IRstuff]

Why is there a bypass capacitor on a pin where you need to do this test? Conversely, why do this test if you have a large capacitor attached to it? Is this a signal pin? Or an unused pin?

TTFN

FAQ731-376

 

[tamethetikbalang]

@geekEE - the 10uA current is the widely used value when checking the circuit protection diode. My last resort is to increase that value, same as your idea. Unfortunately, I don't have the specs for the diode, maybe 1mA would do. What do you think?

@IRstuff - this is an input pin. Maybe the one who designed the DIB did not foresee this would happen. He could have put a relay to connect/disconnect the cap, depending on the tests. By the way, this cap is recommended by the device datasheet.

 

[IRstuff]

Is this forward or reverse? Forward is a no-brainer, since the power dissipated, even at 1 mA is trivial.

Reverse may, or may not, be OK. Typical reverse breakdown is around 30V, so there's be about 30 mW of power, which is not a big deal. However, avalanche breakdown can induce hot electron effects that tend to trap electrons in the field oxide, thereby reducing the breakdown voltage in the region.

TTFN

FAQ731-376

 

[tamethetikbalang]

It has to be forward bias. I guess I have no other choice but to increase the current to minimize the settling time.