SPT9689AIP datasheet(6/8 Pages) CADEKA

6 / 8 page

2/20/01

SPT9689

TYPICAL INTERFACE CIRCUIT

The typical interface circuit using the comparator is shown

in figure 3. Although it needs few external components

and is easy to apply, there are several conditions that

should be noted to achieve optimal performance. The very

high operating speeds of the comparator require careful

layout, decoupling of supplies, and proper design of trans-

mission lines.

Since the SPT9689 comparator is a very high-frequency

and high-gain device, certain layout rules must be fol-

lowed to avoid oscillations. The comparator should be

soldered to the board with component lead lengths kept

as short as possible. A ground plane should be used while

the input impedance to the part is kept as low as possible

to decrease parasitic feedback. If the output board traces

are longer than approximately half an inch, microstripline

techniques must be employed to prevent ringing on the

output waveform. Also, the microstriplines must be termi-

nated at the far end with the characteristic impedance of

the line to prevent reflections. Both supply voltage pins

should be decoupled with high-frequency capacitors as

close to the device as possible. All ground pins and no

connects should be soldered to a common ground plane

to further improve noise immunity. If using the SPT9689

as a single comparator, the outputs of the inactive com-

parator can be grounded, left open, or terminated with

50 ohms to –2 V. All outputs on the active comparator,

whether used or unused, should have identical termina-

tions to minimize ground current switching transients.

Figure 3 – SPT9689 Typical Interface Circuit

Figure 4 – SPT9689 Typical Interface Circuit

with Hysteresis

VIN

+5.0 V

10 µF

0.1 µF

100 pF

10 µF

0.1 µF

100 pF

5.2 V

2 V

10 F

+VCC

VEE

GND

Q Output

VREF

100 pF

10 µF

0.1 µF

ECL

NOTES:

Denotes ground plane.

Ferrite bead. Fair Rite Part # 2643001501.

All resistors are chip type 1%.

0.1 µF and 100 pF capacitors are chip type mounted as close

to the pins as possible.

10 µF tant capacitors have lead lengths <0.25" long.

Represents line termination.

100 pF

VIN

+5.0 V

10 µF

0.1 µF

100 pF

10 µF

0.1 µF

10 µF

0.1 µF

100 pF

5.2 V

2 V

10 µF

2 V

1.3 V

+VCC

VEE

GND

100 W

0 to 200 W

VREF

50 W

NOTES:

Denotes ground plane.

Ferrite bead. Fair Rite Part # 2643001501.

All resistors are chip type 1%.

0.1 µF and 100 pF capacitors are chip type mounted

as close to the pins as possible.

10 µF tant capacitors have lead lengths <0.25" long.

Represents line termination.

Q Output

50 W

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