E649 datasheet(6/14 Pages) SEMTECH

6 / 14 page

 2000 Semtech Corp.

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EDGE HIGH-PERFORMANCE PRODUCTS

Edge649

Application Information

Power Supplies

The Edge649 uses three power supplies – VDD, VCC

and VEE. VDD, typically +5V, is the digital supply for all

of the data inputs and outputs. VCC and VEE are the

analog power supplies for the DUT drivers and

comparators. VCC ranges from +6.5V to +11V, and must

be greater than or equal to VDD + 1.5V.

VEE is the

negative analog power and typically varies from 0V to –

3V.

The Edge649 has several power supply requirements to

protect the part in power supply fault situations, as well

as during power up and power down sequences. VCC

must remain greater than or equal to VDD at all times.

Both VCC and VDD must always be positive (above

ground), and VEE must always be negative (at or below

ground).

The three-diode configuration shown in Figure 5, used

on a once-per-board basis, insures power supply

sequence and fault tolerance.

Figure 5.

Power Supply Protection Scheme

Power Supplies Decoupling

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

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.

VHIGH and VLOW Decoupling

As the VHIGH and VLOW 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

Expanding the Common Mode Range

Although the Edge649 can drive and receive 11V swings,

these 11 V signals can be adjusted over an 14V 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 Edge649 I/O range can be optimized for a

variety of applications (see Figure 6).

Figure 6.

There are three rules which govern the supplies V1 and

V2:

VDD + 1.5V

≤ V1 ≤ +11V

–3V

≤ V2 ≤ 0V

(V1 – V2)

≤ 11V

VCC

VDD

VEE

1N5820 or

Equivalent

Edge 649

VCC

VDD

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