Edge749
TEST AND MEASUREMENT PRODUCTS
Application Information
Power Supplies
The Edge749 uses three power supplies: VDD, VCC and
VEE. VDD is the digital supply for all of the data inputs
and outputs. VCC and VEE are the analog power supplies
for the Edge749 drivers and comparators. In order to
protect the Edge749 and avoid damaging it, the following
power supply requirements must be satisifed at all times:
VEE
≤
GND
≤
VDD
≤
VCC
VEE
≤
All Inputs
≤
VCC at all times
capacitor in parallel with a .001
µF
chip capacitor. A
VCC and VEE plane, or at least a solid power bus, is
recommended for optimal performance.
V
HIGH
and V
LOW
Decoupling
As the V
HIGH
and V
LOW
inputs are unbuffered and must
supply the driver output current, decoupling capacitors
for these inputs are recommended in proportion to the
amount of output current the application requires.
Also,
The three-Schottky diode configuration shown in Figure
5, used on a once-per-board basis, insures power supply
sequence and fault tolerance.
VCC
Expanding the Common Mode Range
Although the Edge749 can drive and receive 18 V swings,
these 18 V signals can be adjusted over an 21 V range.
By using programmable regulators V1 and V2 for the
VCC and VEE supplies (feasible because these two
analog power supplies do not supply driver output
current), the Edge749 I/O range can be optimized for a
variety of applications (see Figure 6).
VDD
1N5820 or
Equivalent
V1
VEE
VCC
Figure 5. Power Supply Protection Scheme
Power-On Sequencing
1. VCC (substrate)
2. VEE
3. VDD
4. Inputs
Power Supplies Decoupling
Power-Off Sequencing
1. Inputs
2. VDD
3. VEE
4. VCC
Edge 749
VDD
V2
Figure 6.
VDD, which provides the digital power, should be
decoupled to GND with a .1
µF
chip capacitor in parallel
with a .001
µF
chip capacitor. The bypass capacitors
should be as close to the device as possible. Power and
ground planes are recommended to provide a low
inductance return path.
VCC and VEE, which power the DUT drivers and receivers,
should also be decoupled to GND with a .1
µF
chip
Revision 3 / October 21, 2002
6
There are three rules which govern the supplies V1 and
V2:
1) +10V < V1 < +18V
2) –3V < V2 < 0V
3) (V1 – V2) < +18V.
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