4

2000 Semtech Corp.

www.semtech.com

EDGE HIGH-PERFORMANCE PRODUCTS

Edge647

the DUT. In this environment, the driver can withstand a

short to any legal DUT voltage for an indefinite period.

In a low impedance application with no additional output

series resistance, care must be exercised and systems

should be designed to check for this condition and tristate

the driver if a short is detected.

The driver does NOT have on-chip short circuit protection

or limitation circuitry.

VBB

VBB is an analog input which establishes the threshold

for all single ended digital input signals.

If SW0 EN*,

SW1 EN*, or SW2 EN* are more positive than VBB, these

inputs are a digital “1".

Conversely, if they are more

negative than VBB, they are a “0".

All digital inputs are wide voltage comparator inputs, so

they are technology independent.

By establishing the

appropriate VBB level for the switch control inputs, and

the appropriate differential input levels for the driver digital

control inputs, the Edge647 may be driven by TTL, ECL,

CMOS, or any custom level circuitry.

Figure 1. Driver Digital Inputs

Figure 2. Driver Differential Digital Inputs

Circuit Description

Driver Description

The Edge647 driver supports three distinct programmable

driver levels; high, low, and termination,

and high

impedance. There are no restrictions between any of these

three levels in that all three may vary independently over

the entire operating voltage range between VCC and VEE.

The DVR EN*, DATA, and VTT EN pins are digital inputs

that control the driver (see Table 1). With DVR EN* low,

DATA determines whether the driver will force VH or VL at

DOUT. With DVR EN* high, VTT EN* controls whether the

driver goes into high impedance or drives VTT.

Table 1. Driver Truth Table

VH, VL, and VTT

VH, VL, and VTT define the logical “1”, “0”, and

“termination” levels of the driver and can be adjusted

anywhere over the range spanned by VCC to VEE. There

is no restriction between VH, VL, and VTT, in that they can

all vary independently over the entire voltage range

determined by the power supply levels.

The VH, VL, and VTT inputs are unbuffered in that they

also provide the driver output current, so the sources of

these voltages must have ample current drive capability.

While VTT is referred to as the termination voltage, it may

also be used as a very high “programming” level on many

memory devices.

Driver Output Protection

The Edge647 is designed to operate in a functional testing

environment where a controlled impedance (typically 50

Ω) is maintained between the pin electronics and the DUT.

In general, there will be an external resistor at the driver

output which series terminates the transmission line to

*

N

E

R

V

DN

E

T

T

VA

T

A

DT

U

O

D

10

X

Z

i

H

11

X

T

T

V

0X0

L

V

0X1

H

V

SW0 EN*

SW1 EN*

SW2 EN*

VBB

DATA

DATA*

DVR EN*

DVR EN

VTT EN

VTT EN*