Teledyne LeCroy PMC2PCI-64 - Manual (Page 5)

4
CURRENT MEASUREMENT
When using the PCI532, the user can measure the +5V current being drawn by the Unit-Under-Test, by just
connecting a voltmeter to J3.
When using the PMC2PCI and PCIX6432 (Rev. C and below), the user can measure the +5V current being
drawn by the UUT using a voltmeter at J3, the current draw for the +12V can be measured by using a voltage
meter at J4 and the current draw for the +3.3V can be measured using voltmeter at J5.
When using the PCIX6432 (Rev. D or higher), the user can measure the current draw on the +5V using a
voltmeter between J3.1 and J3.2. To measure the current draw on the +3.3V measure using a voltmeter
between J3.1 and J3.3, and the measure the current draw on the +12V, measure using a voltmeter between
J3.1 and J3.4.
Every Volt read by the meter represents One Amp. So if the voltmeter reads 0.35, it represents that the Unit-
Under-Test is drawing 350 milliamps of current from +5V supply.
NOTE: If the VIO and +5V are on the same plane on your board, you need to remove JP10 jumper, located
on the extender board, in order to get an accurate current measurement.
CURRENT LIMIT CIRCUITRY
Red LEDs, when illuminated, indicate a short or a very low voltage at the output for their corresponding
voltages. Green LEDs when illuminated, indicate voltages at their corresponding outputs. In the case of the
+5V short from the Unit-Under-Test, the Active Extender will automatically switch the current limit down to
about 200 milliamps and will continue to deliver this current for troubleshooting purposes. On the PCIX-6432
and PMC2PCI boards this feature is extended to cover the +12V and +3.3V as well. In the case of shorts or
excessive current draw for the other voltages the resetable fuses will open up until the problem is corrected.
The current limit value for the +5V is set to 5 Amps with JP8 not installed and 1 Amp with JP8 installed.
CURRENT LIMIT ADJUSTMENTS
FOR PCI532/PCI332
To increase the +5v current limit you must reduce the gain of the current measurement circuitry.
Perform the following reworks:
•
To change the current limit to 7.5A install a 200k Resistor on top of R19 and R22, this will cause
the current measurement circuit gain to be reduced by a factor 0.66 (I.e. 1 volt will represent 1.5
A current draw.)
•
To change the current limit to 10A install a 100k Resistor on top of R19 and R22, this will cause
the current measurement circuit gain to be reduced by a factor 0.50 (I.e. 1 volt will represent 2 A
current draw.)
To increase the +3.3v current limit you must place an additional fuse across F4 which will increase
the current limit to 2A.