MAX968EUA-T Maxim Integrated Products, MAX968EUA-T Datasheet - Page 9

• Manufacturer Part Number: MAX968EUA-T
• Description: Comparator ICs Quad, Micropower, Ul tra-Low-Voltage, Rai
• Manufacturer: Maxim Integrated Products

function below about 1.5V, although the comparators
typically continue to operate with a supply voltage as
low as 1V. At low supply voltages (<1.6V), the input
common-mode range remains rail-to-rail, but the com-
parator’s output sink capability is reduced and propa-
gation delay increases (see Typical Operating
Characteristics).
Figure 1 shows a typical comparator application that
monitors V
voltage trip point (V
1.6V and approaches 1V, the reference voltage typical-
ly falls below the divider voltage (V+). This causes the
comparator output to change state. If OUT’s state must
be maintained under these conditions, a latching circuit
is required.
The MAX965–MAX970 contain a unique slew-rate-
controlled output stage capable of rail-to-rail operation
with an external pull-up resistor. Typical comparators
consume orders of magnitude more current during
switching than during steady-state operation. With the
MAX965 family of comparators, during an output transi-
tion from high to low, the output slew rate is limited to
minimize switching current.
With V
nal 1.235V bandgap reference is ±1.5% accurate over
the commercial temperature range and ±2.5% accu-
rate over the extended temperature range. The REF
output is typically capable of sourcing 50µA. To reduce
reference noise or to provide noise immunity, bypass
REF with a capacitor (0.1nF to 0.1µF).
Figure 1. Operation below 1.6V
Ultra-Low-Voltage, Rail-to-Rail I/O Comparators
V+
CC
R1
47kΩ
R2
150kΩ
greater than 1.6V but less than 5.5V, the inter-
CC
at 1.6V. Resistor divider R1/R2 sets the
REF
V
V
CC
_______________________________________________________________________________________
CC
GND
TRIP
OUT
) at 1.6V. As V
MAX965
100kΩ
Comparator Output
1.6V
1.0V
Voltage Reference
V
CC
R1 =
V
TRIP
= 1.22
CC
V
1.22
TRIP
V
drops below
REF
R1
R2
- 1
Single/Dual/Quad, Micropower,
+ 1
x R2
V+
t
The comparator has an effective wideband peak-to-
peak noise of around 10µV. The voltage reference has
peak-to-peak noise approaching 1.0mV with a 0.1µF
bypass capacitor. Thus, when a comparator is used
with the reference, the combined peak-to-peak noise is
about 1.0mV. This, of course, is much higher than the
individual components’ RMS noise. Avoid capacitive
coupling from any output to the reference pin. Crosstalk
can significantly increase the references’ actual noise.
Many comparators oscillate in the linear region of oper-
ation because of noise or undesired parasitic feed-
back. This tends to occur when the voltage on one
input is equal or very close to the voltage on the other
input. The MAX965–MAX970 have internal hysteresis to
counter parasitic effects and noise. In addition, with the
use of external resistor, the MAX965/MAX967/
MAX968/MAX969’s hysteresis can be programmed to
as much as ±50mV (see the section Adding Hysteresis
to the MAX965/MAX967/MAX968/MAX969).
The hysteresis in a comparator creates two trip points:
one for the rising input voltage and one for the falling
input voltage (Figure 2). The difference between the trip
points is the hysteresis. When the comparator’s input
voltages are equal, the hysteresis effectively causes
one comparator input voltage to move quickly past the
other, thus taking the input out of the region where
oscillation occurs.
Figure 2. Threshold Hysteresis Band
__________Applications Information
V
REF
OUT
IN+
IN-
- V
HYST
V
HB
THRESHOLDS
HYSTERESIS
BAND
Noise Considerations
Hysteresis
9