Note

Powered Testing With Digital Vectors (ICT)
12 Application Note
board under test. To prevent damage, drive only one control signal high at any time during the test
while all others are low.
The High Side switch of each switch pair is used to test a VCCP solder ball and contact along with
the shared signal solder ball and contact of the High and Low Side switch pair. The control line for
the High Side switch is driven to a logic high, thus turning the switch ON and enabling an electrical
connection between VCCP and the shared signal. When this happens, a logic high should be
received on the shared signal. At the same time, the Low Side switch control signal will be at a
logic low.
The Low Side switch of each switch pair is used to test a GND solder ball and contact along with
the shared signal solder ball and contact of the High and Low Side switch pair. The control line for
the Low Side switch is driven to a logic high, thus turning the switch ON and enabling an electrical
connection between GND and the shared signal. A logic low should be received on the shared
signal. At the same time, the High Side switch control signal will be at a logic low.
One shared signal is used to test one VCCP and one GND connection. The lack of the high/low
signal transition would indicate an open on either the shared signal or the power/ground connection
used by that switch pair.
Table 3-2 shows that Signal1, Vccp1, and Gnd1 as well as Signal2, Vccp2, and Gnd2 can be
verified through Hcontrol_0 and Lcontrol_0.
As with all powered digital in-circuit testing, all other active components on the board that are
connected to the socket should be placed in a tri-state mode before testing with this technique.
3.3 Using Test Head Loads
Test head loads (pull-ups/pull-downs) improve the detection of opens. With the switch pair OFF,
the signals would be pulled to a logic level low if test head pull-downs are used and a logic level
high if test head pull-ups are used. Using pull-ups with the Low Side switch ON would receive a
logic level high on the signal if the signal or GND connection were open and a logic level low if
they were not open. Using pull-downs with the High Side switch ON would receive a logic level
low on the signal if the signal or VCCP ball were open and a logic level high if they were not open.
Note: On-board pull-up/down resistors must be taken into consideration when test head loads are
used.
Table 3-2. Control Signals
Signal Name Signal Ball
Hcontrol_0
E5
Lcontrol_0
E6
Hcontrol_1
D1
Lcontrol_1
D14