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E749BPJ

Octal Pin Electronics Driver/Receiver

Semtech Corporation 

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:

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

Also,

VEE ≤ GND ≤ VDD ≤ VCC

VEE ≤ All Inputs ≤ VCC at all times

The three-Schottky diode configuration shown in Figure

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

sequence and fault tolerance.

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

VCC

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

VDD

VCC and VEE supplies (feasible because these two

analog power supplies do not supply driver output

1N5820 or

Equivalent

current), the Edge749 I/O range can be optimized for a

variety of applications (see Figure 6).

VEE

Figure 5. Power Supply Protection Scheme

Power-On Sequencing

1. VCC (substrate)

2. VEE

3. VDD

4. Inputs

Power-Off Sequencing

1. Inputs

2. VDD

3. VEE

4. VCC

V1

VCC

Edge 749

VDD

V2

Power Supplies Decoupling

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.

There are three rules which govern the supplies V1 and

V2:

1) +10V < V1 < +18V

2) –3V < V2 < 0V

3) (V1 – V2) < +18V.

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

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