Single/Dual/Quad High-Speed, Ultra Low-Power,
Single-Supply TTL Comparators
MAX907/MAX908/MAX909
V
TRIP+
V
HYST
V
IN+
V
+ V
TRIP-
V
OS
=
TRIP+
2
V
IN-
= 0V
3V
LE
1.4V
0
COMPARE
t
s
t
h
LATCH
V
TRIP-
V
OS
V
OH
COMPARATOR
OUTPUT
V
OL
DIFFERENTIAL
INPUT
VOLTAGE
V
OH
OUTPUT
1.4V
(QOUT)
V
OL
V
OD
V
IN
t
PD
+
Figure 1. Input and Output Waveforms, Noninverting Input
Varied
t
SKEW
V
OH
OUTPUT
(QOUT) 1.4V
V
OL
__________Applications Information
Circuit Layout
Because of the MAX907/MAX908/MAX909’s high gain
bandwidth, special precautions must be taken to real-
ize the full high-speed capability. A printed circuit
board with a good, low-inductance ground plane is
mandatory. Place the decoupling capacitor (a 0.1µF
ceramic capacitor is a good choice) as close to V+ as
possible. Pay close attention to the decoupling capaci-
tor’s bandwidth, keeping leads short. Short lead
lengths on the inputs and outputs are also essential to
avoid unwanted parasitic feedback around the com-
parators. Solder the device directly to the printed cir-
cuit board instead of using a socket.
Figure 2. MAX909 Timing Diagram
Battery-Operated Infrared Data Link
Figure 4's circuit allows reception of infrared data. The
MAX403 converts the photodiode current to a voltage,
and the MAX907 determines whether the amplifier output
is high enough to be called a “1”. The current consump-
tion of this circuit is minimal: The MAX403 and MAX907
require typically 250µA and 700µA, respectively.
Overdriving the Inputs
The inputs to the MAX907/MAX908/MAX909 may be
driven beyond the voltage limits given in the
Absolute
Maximum Ratings,
as long as the current flowing into
the device is limited to 25mA. However, if the inputs
are overdriven, the output may be inverted. The addi-
tion of an external diode prevents this inversion by limit-
ing the input voltage to 200mV to 300mV below ground
(see Figure 3).
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