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E211ATF

Dual Pin Electronics Driver

Semtech Corporation 

Edge211

TEST AND MEASUREMENT PRODUCTS

Application Information

Power Supplies Decoupling

Latchup Protection

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.

The Edge211 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 (external supply

for the digital logic) 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 2 should

be used on a once-per-board basis.

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 Ω into a 50 Ω transmission line) are

the maximum dynamic output currents the driver should

see. The decoupling capacitors should be able to provide

this current 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

associated with each function and recharging the

capacitors, rather than providing the actual dynamic

currents required to drive the DUT transmission line.

Ideally, VH, VL, and VTT would each have a dedicated

power layer on the PC board for the lowest possible

inductance power supply distribution.

Power Supply Sequencing

The following sequence should be used when powering

up the Edge211.

1. VCC

2. VEE

3. Analog inputs (VH, VL , VTT)

4. Digital inputs (VTTEN, DVREN, DATA)

VCC

VDD

1N5820 or

Equivalent

External

System

Ground

VEE

Figure 2.

Power Supply Protection Scheme

gure 5.

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 system

power supplies are capable of supplying large

amounts of current. Even if the device is not

immediately destroyed, the cumulative damage

caused by the stress of repeated latchup may affect

device reliability.

2005 Semtech Corp., Rev. 6, 2/28/05

6

www .semtech.com

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