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3/1/01

SPT9693

TYPICAL INTERFACE CIRCUIT

The typical interface circuit using the comparator is shown

in figure 2. 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 SPT9693 comparator is a very high-frequency

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

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 de-

crease 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. All supply voltages should

be decoupled with high-frequency capacitors as close to

the device as possible. If using the SPT9693 as a single

comparator, the outputs of the inactive comparator can be

grounded, left open or terminated with 50 ohms to –2 V. All

outputs on the active comparator, whether used or un-

used, should have identical terminations to minimize

ground current switching transients.

All ground pins should be connected to the same ground

plane to further improve noise immunity and shielding.

Unused outputs must be terminated with 50 ohms to

ground.

Figure 2 – SPT9693 Typical Interface Circuit

Figure 3 – SPT9693 Typical Interface Circuit

with Hysteresis

LE

LE

+

–

Q Output

550 W

»

Notes:

1) D1 = 1N5231B or 1N751 or equivalent.

2) D2 = 1N914 or equivalent.

3) At no time should both inputs be allowed to float with power applied

to the device. At least one of the inputs should be tied to a voltage

within the common mode range (–3.0 to +8.0 V) to prevent possible

damage to the device. Additional protection diodes D2 should be used

on the inputs if there is the possibility of exceeding the absolute

maximum ratings.

.1 µF

–2 V

Q Output

50 W

50 W

LE

LE

+

–

Q Output

550 W

»

Notes:

1) D1 = 1N5231B or 1N751 or equivalent.

2) D2 = 1N914 or equivalent.

3) At no time should both inputs be allowed to float with power applied

to the device. At least one of the inputs should be tied to a voltage

within the common mode range (–3.0 to +8.0 V) to prevent possible

damage to the device. Additional protection diodes D2 should be

used on the inputs if there is the possibility of exceeding the absolute

maximum ratings.

0.1 µF

–2 V

Q Output

100 W

0 to 200 W

–2 V

–1.3 V

50 W

0.1 µF

50 W