FEC200 VT Test
This applies to MAXX software beta version dated between 10/1/97 and 12/31/97. Ask us about any other versions.
The VT test can perform VT only or a combination of VT and IH (go, nogo). To test just VT, program one forcing condition only as in the following.
- TESTn VT 10A >1V >4V
If you want to do the IH (go, nogo) option also, add a second forcing current as follows.
- TESTn VT 10A 200MA >1V <4V
The 200 MA is the IH limit.
HOW IT WORKS
Since the 500V supply in the FEC200 has a slew rate of about 100V/mS, a preliminary forcing condition of 100µA is applied for about 7mS to allow the voltage to ramp up to VBR at that current.
Next the VT forcing current is applied, initially with, both the negative low voltage, high current and the positive high voltage, moderate current supplies enabled and applied to opposite ends of the DUT. The voltage and current begin to ramp up. The negative low voltage supply is moderately fast so the voltage goes up to compliance (if necessary). The positive supply increases (if it is needed) at its usual 100V/mS.
At some point the VBO and IBO point is reached and the device turns on. A large rectifier from the positive side to ground can bypass the "ON" current to common thereby bypassing the high voltage supply, which is now turned off. About 600µS is allowed for this process. It is assumed that the roughly -20V of the low voltage supply and the roughly +60V increase in the positive supply in that time is enough to raise the voltage from VBR to VBO.
Now there is an additional "Soak" time, which by default is about 300µS. You can program it longer if you wish.
Next the instantaneous value of VT is locked into a "Track/Hold" and then digitized. The ADC process takes about 1mS, during which time the current continues to flow.
If this is a "VT only" test the power is now removed and the reading compared with the limits. If a second forcing current is programmed however, the VT is remembered for later use and then the current begins an exponential decay which reaches 50% in about *560µS. (See CUSTOM.TXT about this timing). The exponential is floored at the IH limit programmed and when that level is reached, the voltage is again measured to find if the part has "tuned off."
The threshold for that is two times the maximum VT limit or 16V, whichever is lower.
If the part fails the IH test it is forced to fail the whole test even if the VT is within limits.