MAX999EUK-T(2014) Ver la hoja de datos (PDF) - Maxim Integrated

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MAX999EUK-T
(Rev.:2014)

Single/Dual/Quad, Ultra-High-Speed, +3V/+5V, Beyond-the-Rails Comparators

Maxim Integrated 

MAX961–MAX964/

MAX997/MAX999

Single/Dual/Quad, Ultra-High-Speed, +3V/+5V,

Beyond-the-Rails Comparators

Detailed Description

The MAX961–MAX964/MAX997/MAX999 single-supply

comparators feature internal hysteresis, ultra-high-speed

operation, and low power consumption. Their outputs are

guaranteed to pull within 0.52V of either rail without exter-

nal pullup or pulldown circuitry. Beyond-the-Rails input

voltage range and low-voltage, single-supply operation

make these devices ideal for portable equipment. These

comparators all interface directly to CMOS logic.

Timing

Most high-speed comparators oscillate in the linear region

because of noise or undesirable parasitic feedback. This

can occur when the voltage on one input is close to or

equal to the voltage on the other input. These devices

have a small amount of internal hysteresis to counter

parasitic effects and noise.

The added hysteresis of the MAX961–MAX964/MAX997/

MAX999 creates two trip points: one for the rising input

voltage and one for the falling input voltage (Figure 1).

The difference between the trip points is the hysteresis.

When the comparator’s input voltages are equal, the hys-

teresis effectively causes one comparator input voltage to

move quickly past the other, thus taking the input out of

the region where oscillation occurs. Standard compara-

tors require hysteresis to be added with external resistors.

The fixed internal hysteresis eliminates these resistors.

The MAX961/MAX963 include internal latches that allow

storage of comparison results. LE has a high input

impedance. If LE is low, the latch is transparent (i.e., the

comparator operates as though the latch is not present).

The comparator’s output state is stored when LE is pulled

high. All timing constraints must be met when using the

latch function (Figure 2).

Input Stage Circuitry

The MAX961–MAX964/MAX997/MAX999 include internal

protection circuitry that prevents damage to the preci-

sion input stage from large differential input voltages.

This protection circuitry consists of two groups of three

front-to-back diodes between IN+ and IN-, as well as two

200Ω resistors (Figure 3). The diodes limit the differential

voltage applied to the comparator’s internal circuitry to no

more than 3VF, where VF is the diode’s forward-voltage

drop (about 0.7V at +25°C).

VTRIP+

VHYST

VTRIP-

VIN+

VOS = VTRIP+ + VTRIP-

2

VIN- = 0V

VOH

Q

VOL

Q

VOH

VOL

Figure 1. Input and Output Waveforms, Noninverting Input Varied

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