EDGE646ATF View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'EDGE646ATF' PDF : 14 Pages View PDF
Edge646
TEST AND MEASUREMENT PRODUCTS
Application Information
PRELIMINARY
Power Supplies
Power Supplies Decoupling
The Edge646 uses two power supplies for circuit opera-
tion; VCC and VEE. In order to protect the Edge646 and
avoid damaging it, the following power supply requirements
must be satisifed at all times:
VEE ≤ All Inputs ≤ VCC
The sequence below can be used as a guideline when
operating the Edge646:
A .1 µF capacitor is recommended between VCC and VEE.
In addition, solid VCC and VEE planes are recommended
to provide a low inductance path for the power supply
currents. These planes will reduce any inductive supply
drops associated with swtiching currents on the power
supply pins. If solid planes are not possible, then wide
power busses are preferable.
Power-On Sequencing
1. VCC (substrate)
2. VEE
3. Inputs
Power-Off Sequencing
1. Inputs
2. VEE
3. VCC
The two diode configuration shown in Figure 3 should be
used on a once-per-board basis to ensure power supply
sequence and fault tolerance.
VCC
1N5820 or
Equivalent
VH, VL, and VTT Decoupling
As the VH, VL, and VTT 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. In general, a
surge current of 50 mA (5V swings series terminated with
50 Ohms into a 50 Ohm transmission line) are the maxi-
mum dynamic output currents the driver should see. The
decoupling capacitors should be able to provide this cur-
rent for the duration of the round trip time between the
pin electronics and the DUT, and then recharge themselves
before the next such transition would occur. Once this
condition is satisfied, the VH, VL, and VTT supply voltages
are more responsible for establishing the DC levels asso-
ciated with each function and recharging the capacitors,
rather than providing the actual dynamic currents required
to drive the DUT transmission line.
VEE
Figure 3. Power Supply Protection Scheme
Ideally, VH, VL, and VTT would each have a dedicated power
layer on the PC board for the lowest possible inductance
power supply distribution.
Warning: It is extremely important that the voltage
on any device pin does not exceed the range of VEE
–0.5V to VCC +0.5V at any time, either during power
up, normal operation, or during power down. Failure
to adhere to this requirement could result in latchup
of the device, which could be destructive if the sys-
tem power supplies are capable of supplying large
amounts of current. Even if the device is not imme-
diately destroyed, the cumulative damage caused by
the stress of repeated latchup may affect device re-
liability.
Revision 2 / October 21, 2002
6
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