MAX976ESA Maxim Integrated Products, MAX976ESA Datasheet - Page 6

• Manufacturer Part Number: MAX976ESA
• Description: Audio Amplifiers Stereo 3W Audio Powe r Amplifiers with He
• Manufacturer: Maxim Integrated Products

Single/Dual/Quad, SOT23, Single-Supply,
High-Speed, Low-Power Comparators
High-speed comparators can oscillate in the linear
operating region because of noise or undesired para-
sitic feedback. This tends to occur when the voltage on
one input is equal to or very close to the voltage on the
other input. The MAX976/MAX978/MAX998 have inter-
nal hysteresis to counter parasitic effects and noise.
The hysteresis in a comparator creates two trip points:
one for the rising input voltage and one for the falling
input voltage (Figure 1). The difference between the trip
points is the hysteresis. When the comparator input
voltages are equal, the hysteresis effectively causes
one comparator input voltage to move quickly past the
other, taking the input out of the region where oscilla-
tion occurs.
Figure 1 illustrates the case where IN- has a fixed volt-
age applied and IN+ is varied. If the inputs were
reversed, the figure would be the same, except with an
inverted output.
The MAX976/MAX978/MAX998 input common-mode
voltage range is from -0.2V to (V
range for each comparator input extends to both V
and GND. The output remains in the correct logic state
while one or both of the inputs are within the common-
mode range. If both input levels are out of the common-
mode range, input-stage current saturation occurs, and
the output becomes unpredictable.
The MAX998 features a low-power shutdown mode,
which is activated by forcing SHDN low. Shutdown
mode reduces the supply current to 1nA (typical), dis-
ables the comparator, and places the output in a high-
impedance state. Drive SHDN high to enable the
comparator. Do not leave SHDN unconnected. Since it
is a high-impedance input, leaving SHDN unconnected
could result in indeterminate logic levels, adversely
Figure 1. Input and Output Waveforms, Noninverting Input
Varied
6
V
_______________________________________________________________________________________
IN+
COMPARATOR
V
V
V
TRIP+
HYST
TRIP-
OUTPUT
Input-Stage Circuitry
CC
Shutdown Mode
- 1.2V). The voltage
V
V
V
V
OS
IN-
OH
OL
Hysteresis
= V
= 0
TRIP+
+ V
2
TRIP-
CC
affecting comparator operation. Likewise, do not three-
state SHDN. Due to the output leakage currents of
three-state devices and the small internal current for
SHDN, three-stating this pin could also result in indeter-
minate logic levels.
The maximum input voltage for SHDN is 6V, referred to
GND, and is not limited by V
5V logic to drive SHDN while V
voltage, such as 3V. The logic threshold limits for
SHDN are proportional to V
Characteristics).
The MAX976/MAX978/MAX998 have a high-gain band-
width and require careful board layout. We recommend
the following design guidelines:
1) Use a printed circuit board with an unbroken, low-
2) Place a decoupling capacitor (a 0.1µF ceramic
3) Keep lead lengths short on the inputs and outputs
4) Solder the devices directly to the printed circuit
5) Minimize input impedance.
6) For slowly varying inputs, use a small capacitor
Generate additional hysteresis with three resistors
using positive feedback, as shown in Figure 2. This
positive feedback method slows the hysteresis
response time. Calculate resistor values as follows:
1) Select R3. The leakage current of IN+ is typically
_____________Applications Information
75nA, so the current through R3 should be at least
1.0µA to minimize errors caused by leakage current.
The current through R3 at the trip point is (V
V
when solving for R3. The two formulas are:
Use the smaller of the two resulting resistor values.
For example, if V
resistor values are 1.2MΩ and 3.8MΩ. Choose a
standard value for R3 of 1.2MΩ.
inductance ground plane. Surface-mount compo-
nents are recommended.
capacitor is a good choice) between V
ground as close to the pins as possible.
to avoid unwanted parasitic feedback around the
comparators.
board instead of using a socket.
(~1000pF) across the inputs to improve stability.
OUT
R3 = V
R3 = (V
) / R3. Consider the two possible output states
REF
or
CC
Circuit Layout and Bypassing
/ 1.0µA
- V
REF
REF
= 1.2V and V
) / 1.0µA
Additional Hysteresis
CC
CC
. This allows the use of
CC
operates at a lower
CC
(see Electrical
= 5.0V, the two
CC
REF
and
-