AD8465

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CROSSOVER BIAS POINTS

The AD8465 comparator offers a programmable hysteresis

feature that significantly improves accuracy and stability.

Connecting an external pull-down resistor or a current source

from the LE/HYS pin to GND varies the amount of hysteresis

in a predictable and stable manner. Leaving the LE/HYS pin

disconnected or driving it high removes hysteresis. The maxi-

mum hysteresis that can be applied using this pin is approximately

160 mV. Figure 19 illustrates the amount of hysteresis applied as

a function of external resistor value. Figure 10 illustrates hysteresis

as a function of current.

Rail-to-rail inputs of this type, in both op amps and comparators,

have a dual front-end design. Certain devices are active near the

mined point in the common-mode range, a crossover occurs.

reverses and there are changes in measured offset voltages and

currents.

MINIMUM INPUT SLEW RATE REQUIREMENT

With the rated load capacitance and normal good PCB design

practice, as discussed in the Optimizing Performance section,

these comparators should be stable at any input slew rate with

no hysteresis. Broadband noise from the input stage is observed

in place of the violent chattering seen with most other high

speed comparators. With additional capacitive loading or

poor bypassing, oscillation is observed. This oscillation is

due to the high gain bandwidth of the comparator in combina-

tion with feedback parasitics in the package and PCB. In many

applications, chattering is not harmful.

The hysteresis control pin appears as a 1.25 V bias voltage

seen through a series resistance of 70 kΩ ± 20% throughout the

hysteresis control range. The advantages of applying hysteresis

in this manner are improved accuracy, improved stability, reduced

component count, and maximum versatility. An external bypass

capacitor is not recommended on the LE/HYS pin because it

would likely degrade the jitter performance of the device and

impair the latch function. As described in the Using/Disabling

the Latch Feature section, hysteresis control need not compro-

mise the latch function.

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HYSTERESIS RESISTOR (kΩ)