MAX985ESA-T Maxim Integrated Products, MAX985ESA-T Datasheet - Page 7

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MAX985ESA-T

Manufacturer Part Number
MAX985ESA-T
Description
Comparator ICs Micropower, Low-Volt age, SOT23, Rail-to-
Manufacturer
Maxim Integrated Products
Datasheet
The MAX985/MAX986/MAX989/MAX990/MAX993/
MAX994 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 11µA.
Their common-mode input voltage range extends 0.25V
beyond each rail. Internal hysteresis ensures clean out-
put 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 MAX985/MAX989/MAX993 have a
push-pull output structure that sinks as well as sources
current. The MAX986/MAX990/MAX994 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
graph Supply Current vs. Output Transition Frequency
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. Another advantage realized in high-
speed, battery-powered applications is a substantial
increase in battery life.
_______________Detailed Description
CC
+ 0.25V). These comparators may oper-
_______________________________________________________________________________________
Micropower, Low-Voltage, UCSP/SC70,
Output Stage Circuitry
Input Stage Circuitry
EE
.
CC
Rail-to-Rail I/O Comparators
to an
The MAX985/MAX989/MAX993 have ±3mV 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 MAX985/MAX989/MAX993.
1) Select R3. Leakage current at IN is under 10nA, so
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 (MAX985/MAX989/MAX993)
V
__________Applications Information
IN
the current through R3 should be at least 1µA to
minimize errors caused by leakage current. The cur-
rent through R3 at the trip point is (V
R3. Considering the two possible output states in
solving for R3 yields two formulas: R3 = V
or R3 = (V
two resulting resistor values. For example, if V
1.2V and V
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.
R1
R2
REF
CC
R1 = R3 x (V
= 5V, then the two R3 resistor values
- V
V
REF
CC
IN
IN
) / 1µA. Use the smaller of the
R3
falling). This is the threshold
rises above the trip point. For
Additional Hysteresis
MAX985/MAX989/MAX993
V
V
V
HB
CC
CC
EE
IN
/ V
rising (V
CC
OUT
MAX985
MAX989
MAX993
)
REF
THR
HB
REF
). For this
- V
; V
OUT
THF
REF
/ 1µA
) /
is
=
7

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