MAX992 Maxim, MAX992 Datasheet - Page 8

• Manufacturer Part Number: MAX992
• Description: The MAX987/MAX988/MAX991/MAX992/MAX995/ MAX996 single/dual/quad micropower comparators feature low-voltage operation and rail-to-rail inputs and outputs
• Manufacturer: Maxim

High-Speed, Micropower, Low-Voltage,
SOT23, Rail-to-Rail I/O Comparators
The MAX987/MAX988/MAX991/MAX992/MAX995/
MAX996 are single/dual/quad low-power, low-voltage
comparators. They have an operating supply voltage
range between +2.5V and +5.5V and consume only
48µA per comparator, while achieving 120ns propaga-
tion delay. Their common-mode input voltage range
extends 0.25V beyond each rail. Internal hysteresis
ensures clean output switching, even with slow-moving
input signals. Large internal output drivers allow rail-to-
rail output swing with up to 8mA loads.
The output stage employs a unique design that mini-
mizes supply-current surges while switching, virtually
eliminating the supply glitches typical of many other
comparators. The MAX987/MAX991/MAX995 have a
push-pull output structure that sinks as well as sources
current. The MAX988/MAX992/MAX996 have an open-
drain output stage that can be pulled beyond V
absolute maximum of 6V above V
The devices’ input common-mode range extends from
-0.25V to (V
ate at any differential input voltage within these limits.
Input bias current is typically 1.0pA if the input voltage
is between the supply rails. Comparator inputs are pro-
tected from overvoltage by internal body diodes con-
nected to the supply rails. As the input voltage exceeds
the supply rails, these body diodes become forward
biased and begin to conduct. Consequently, bias cur-
rents increase exponentially as the input voltage
exceeds the supply rails.
These comparators contain a unique output stage
capable of rail-to-rail operation with up to 8mA loads.
Many comparators consume orders of magnitude more
current during switching than during steady-state oper-
ation. However, with this family of comparators, the
supply-current change during an output transition is
extremely small. The Typical Operating Characteristics
Supply Current vs. Output Transition Frequency graph
shows the minimal supply-current increase as the out-
put switching frequency approaches 1MHz. This char-
acteristic eliminates the need for power-supply filter
capacitors to reduce glitches created by comparator
switching currents. Battery life increases substantially
in high-speed, battery-powered applications.
8
_______________________________________________________________________________________
CC
+ 0.25V). These comparators may oper-
Detailed Description
Output Stage Circuitry
Input Stage Circuitry
EE
.
CC
to an
The MAX987/MAX991/MAX995 have ±2.5mV internal
hysteresis. Additional hysteresis can be generated with
three resistors using positive feedback (Figure 1).
Unfortunately, this method also slows hysteresis
response time. Use the following procedure to calcu-
late resistor values for the MAX987/MAX991/MAX995.
1) Select R3. Leakage current at IN is under 10nA;
2) Choose the hysteresis band required (V
3) Calculate R1 according to the following equation:
4) Choose the trip point for V
Figure 1. Additional Hysteresis (MAX987/MAX991/MAX995)
therefore, the current through R3 should be at least
1µA to minimize errors caused by leakage current.
The current through R3 at the trip point is (V
V
states and solving for R3 yields two formulas: R3 =
V
smaller of the two resulting resistor values. For
example, if V
R3 resistor values are 1.2MΩ and 3.8MΩ. Choose a
1.2MΩ standard value for R3.
example, choose 50mV.
For this example, insert the values R1 = 1.2MΩ x
(50mV / 5V) = 12kΩ.
the trip point for V
voltage at which the comparator switches its output
from low to high as V
this example, choose 3V.
OUT
REF
V
IN
) / R3. Considering the two possible output
/ 1µA or R3 = (V
R1
Applications Information
REF
R1 = R3 x (V
R2
= 1.2V and V
IN
IN
V
REF
falling). This is the threshold
rises above the trip point. For
REF
Additional Hysteresis
MAX987/MAX991/MAX995
R3
HB
IN
- V
/ V
CC
V
V
V
rising (V
CC
CC
EE
CC
CC
= 5V, then the two
) / 1µA. Use the
)
OUT
MAX987
MAX991
MAX995
0.1µF
THR
HB
). For this
; V
THF
REF
is
-