MAX961 Maxim, MAX961 Datasheet - Page 8

• Manufacturer Part Number: MAX961
• Description: The MAX961–MAX964/MAX997/MAX999 are low-power, ultra-high-speed comparators with internal hysteresis
• Manufacturer: Maxim

Single/Dual/Quad, Ultra-High-Speed, +3V/+5V,
Beyond-the-Rails Comparators
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 external 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.
Most high-speed comparators oscillate in the linear
region because of noise or undesirable parasitic feed-
back. 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 hystere-
sis 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
hysteresis effectively causes one comparator input
Figure 1. Input and Output Waveforms, Noninverting Input Varied
8
_______________Detailed Description
_______________________________________________________________________________________
V
V
V
TRIP+
HYST
TRIP-
Q
Q
Timing
voltage to move quickly past the other, thus taking the
input out of the region where oscillation occurs. Standard
comparators 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 pre-
sent). 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).
The MAX961–MAX964/MAX997/MAX999 include inter-
nal protection circuitry that prevents damage to the pre-
cision 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 dif-
ferential voltage applied to the comparator’s internal
circuitry to no more than 3V
forward-voltage drop (about 0.7V at +25°C).
V
IN+
V
V
OS
IN-
= 0V
=
V
TRIP+
V
V
V
V
OH
OL
OH
OL
+ V
2
TRIP-
Input Stage Circuitry
F
, where V
F
is the diode’s