80960KB
14
of a matched diode bridge. Since the open-drain
outputs sink current, only the I
OL
legs of the bridge
are necessary and the I
OH
legs are not used. When
the 80960KB driver under test is turned off, the
output pin is pulled up to V
REF
(i.e., V
OH
). Diode D
1
is turned off and the I
OL
current source flows through
diode D
2
.
When the 80960KB open-drain driver under test is
on, diode D
1
is also on and the voltage on the pin
being tested drops to V
OL
. Diode D
2
turns off and I
OL
flows through diode D
1
.
Figure 12. Test Load Circuit for Three-State
Output Pins
Figure 13. Test Load Circuit for Open-Drain
Output Pins
THREE-STATE OUTPUT
C
L
= 50 pF for all signals
C
L
C
L
OPEN-DRAIN OUTPUT
I
OL
D
2
I
OL
Tested at 25 mA
V
REF
= V
CC
D1 and D
2
are matched
D
1
C
L
= 50 pF for all signals
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