MAX908 Maxim, MAX908 Datasheet - Page 10

• Manufacturer Part Number: MAX908
• Description: The MAX907/MAX908/MAX909 are dual/quad/single, high-speed, ultra-low-power voltage comparators designed for use in systems powered from a single +5V supply; the MAX909 also accepts dual ±5V supplies
• Manufacturer: Maxim

Dual/Quad/Single, High-Speed, Ultra-Low-Power,
Figure 1. Input and Output Waveforms, Noninverting Input
Varied
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 circuit
board instead of using a socket.
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 addition of
an external diode prevents this inversion by limiting the
input voltage to 200mV to 300mV below ground
(Figure 3).
V
V
COMPARATOR
V
TRIP+
TRIP-
HYST
OUTPUT
Applications Information
_______________________________________________________________________________________
Overdriving the Inputs
V
Circuit Layout
IN+
Single-Supply TTL Comparators
V
V
OS
IN-
=
= 0V
V
TRIP+
V
V
OH
OL
2
+ V
TRIP-
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.
Figure 2. MAX909 Timing Diagram
DIFFERENTIAL
VOLTAGE
OUTPUT
OUTPUT
(QOUT)
(QOUT)
INPUT
Battery-Operated Infrared Data Link
LE
1.4V
1.4V
1.4V
V
V
V
V
V
3V
0V
OH
OH
OS
OL
OL
COMPARE
t
s
V
V
IN
OD
t
h
t
PD
LATCH
+
t
SKEW
9