Applications Information

Circuit Layout

Because of the large gain-bandwidth transfer function

of the MAX9201/MAX9202/MAX9203 special precau-

tions must be taken to realize their full high-speed

capability. A printed circuit board with a good, low-

inductance ground plane is mandatory. All decoupling

capacitors (the small 100nF ceramic type is a good

choice) should be mounted as close as possible to the

power-supply pins. Separate decoupling capacitors for

Close attention should be paid to the bandwidth of the

decoupling and terminating components. Short lead

lengths on the inputs and outputs are essential to avoid

unwanted parasitic feedback around the comparators.

Solder the device directly to the printed circuit board

instead of using a socket.

Input Slew-Rate Requirements

As with all high-speed comparators, the high gain-band-

width product of the MAX9201/MAX9202/ MAX9203 can

create oscillation problems when the input traverses the

linear region. For clean output switching without oscilla-

tion or steps in the output waveform, the input must meet

minimum slew-rate requirements (0.5V/s typ). Oscillation

is largely a function of board layout and of coupled

source impedance and stray input capacitance. Both

poor layout and large source impedance will cause the

part to oscillate and increase the minimum slew-rate

requirement. In some applications, it may be helpful to

apply some positive feedback between the output and

positive input. This pushes the output through the transi-

tion region clearly, but applies a hysteresis in threshold

seen at the input terminals.

TTL Output and Latch Inputs

The comparator TTL output stages are optimized for

driving low-power Schottky TTL with a fan-out of four.

When the latch is connected to a logic high level, the

comparator is transparent and immediately responds to

changes at the input terminals. When the latch is con-

nected to a TTL low level, the comparator output latch-

es (in the same state) the instant that the latch

command is applied, and will not respond to subse-

quent changes at the input. No latch is provided on

the MAX9201.

6

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Low Cost, 7ns, Low-Power

Voltage Comparators

PIN

SO

SOT

NAME

FUNCTION

18

Positive Analog Supply

2

7

IN+

Positive Input

3

6

IN-

Negative Input

Negative Analog Supply and

Substrate

54

LATCH

Latch Input

6

3

GND

Ground

7

2

OUT

Output

81

Positive Digital Supply

Pin Description (continued)

GND

OUT

+10V

+5V

GND

OUT

+5V

GND

OUT

+5V

+5V

-5V

Typical Power-Supply Alternatives

Figure 1a. Separate Analog Supply,

Common Ground

Figure 1b. Single +5V Supply, Common

Ground

Figure 1c. Split ±5V Supply, Separate

Ground

MAX9203