SN74S1053

16-BIT SCHOTTKY BARRIER DIODE

BUS-TERMINATION ARRAY

SDLS017A – SEPTEMBER 1990 – REVISED AUGUST 1997

4

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

Large negative transients occurring at the inputs of memory devices (DRAMs, SRAMs, EPROMs, etc.) or on the

CLOCK lines of many clocked devices can result in improper operation of the devices. The SN74S1053 diode

termination array helps suppress negative transients caused by transmission-line reflections, crosstalk, and

switching noise.

Diode terminations have several advantages when compared to resistor termination schemes. Split resistor or

Thevenin equivalent termination can cause a substantial increase in power consumption. The use of a single resistor

to ground to terminate a line usually results in degradation of the output high level, resulting in reduced noise immunity.

Series damping resistors placed on the outputs of the driver reduce negative transients, but they also can increase

propagation delays down the line, as a series resistor reduces the output drive capability of the driving device. Diode

terminations have none of these drawbacks.

The operation of the diode arrays in reducing negative transients is explained in the following figures. The diode

conducts current when the voltage reaches a negative value large enough for the diode to turn on. Suppression of

negative transients is tracked by the current-voltage characteristic curve for that diode. Typical current versus voltage

curves for the SN74S1053 are shown in Figures 3 and 4.

To illustrate how the diode arrays act to reduce negative transients at the end of a transmission line, the test setup

in Figure 5 was evaluated. The resulting waveforms with and without the diode are shown in Figure 6.

The maximum effectiveness of the diode arrays in suppressing negative transients occurs when the diode arrays are

placed at the end of a line and/or the end of a long stub branching off a main transmission line. The diodes also can

be used to reduce the negative transients that occur due to discontinuities in the middle of a line. An example of this

is a slot in a backplane that is provided for an add-on card.

VI – Forward Voltage – V

DIODE FORWARD CURRENT

vs

DIODE FORWARD VOLTAGE

–50

–40

–20

–10

0

–90

–30

0

0.2

0.4

0.6

0.8

1

1.2

–70

–60

–80

–100

1.4

1.6

1.8

2

TA = 25°C

Figure 3. Typical Input Current vs Input Voltage

(Lower Diode)