__________Applications Information

Circuit Layout

Because of the MAX907/MAX908/MAX909’s high gain

bandwidth, special precautions must be taken to real-

ize the full high-speed capability. A printed circuit

board with a good, low-inductance ground plane is

mandatory. Place the decoupling capacitor (a 0.1µF

ceramic capacitor is a good choice) as close to V+ as

possible. Pay close attention to the decoupling capaci-

tor’s bandwidth, keeping leads short. Short lead

lengths on the inputs and outputs are also essential to

avoid unwanted parasitic feedback around the com-

parators. Solder the device directly to the printed cir-

cuit board instead of using a socket.

Overdriving the Inputs

The inputs to the MAX907/MAX908/MAX909 may be

driven beyond the voltage limits given in the

Absolute

Maximum Ratings, as long as the current flowing into

the device is limited to 25mA. However, if the inputs

are overdriven, the output may be inverted. The addi-

tion of an external diode prevents this inversion by limit-

ing the input voltage to 200mV to 300mV below ground

(see Figure 3).

Battery-Operated Infrared Data Link

Figure 4's circuit allows reception of infrared data. The

MAX403 converts the photodiode current to a voltage,

and the MAX907 determines whether the amplifier output

is high enough to be called a “1”. The current consump-

tion of this circuit is minimal: The MAX403 and MAX907

require typically 250µA and 700µA, respectively.

Single/Dual/Quad High-Speed, Ultra Low-Power,

Single-Supply TTL Comparators

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9

COMPARATOR

OUTPUT

2

Figure 1. Input and Output Waveforms, Noninverting Input

Varied

3V

1.4V

0

1.4V

1.4V

COMPARE

LATCH

LE

DIFFERENTIAL

INPUT

VOLTAGE

OUTPUT

(QOUT)

OUTPUT

(

QOUT)

Figure 2. MAX909 Timing Diagram