MAX4291 Maxim, MAX4291 Datasheet - Page 11

• Manufacturer Part Number: MAX4291
• Description: The MAX4291/MAX4292/MAX4294 family of micropower operational amplifiers operates from a 1
• Manufacturer: Maxim

Figure 7a. Using a Resistor to Isolate a Capacitive Load from
the Op Amp
Figure 7b. Pulse Response Without Isolating Resistor
within 100mV of V
load resistor to V
The same application can drive a 220k
when terminated in V
The MAX4291/MAX4292/MAX4294 are unity-gain stable
for loads up to 100pF (see the Load Resistor vs.
Capacitive Load graph in the Typical Operating
Characteristics). Applications that require greater
capacitive-drive capability should use an isolation
IN
OUT
R
IN
L
V
CC
(1.8V
= 2.4V, R
EE
CC
3.5mA
______________________________________________________________________________________
:
MAX4291
MAX4292
MAX4294
L =
CC
2k TO V
and is capable of driving a 485
Driving Capacitive Loads
0.1V)
/2 (0.9V in this case).
10 s/div
EE,
C
R
L
ISO
= 1000pF
485
R
L
A
V
=
R
L
R
+ R
to V
L
100mV
0
100mV
0
ISO
C
load resistor
L
EE
1
OUT
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
resistor between the output and the capacitive load
(Figure 7). Note that this alternative results in a loss of
gain accuracy because R
with the load resistor.
The MAX4291/MAX4292/MAX4294 family operates from
either a single 1.8V to 5.5V supply or dual ±0.9V to
±2.75V supplies. For single-supply operation, bypass
the power supply with a 100nF capacitor to V
case GND). For dual-supply operation, both the V
and the V
with separate 100nF capacitors.
Good PC board layout techniques optimize perfor-
mance by decreasing the amount of stray capacitance
at the op amp’s inputs and output. To decrease stray
capacitance, minimize trace lengths and widths by
placing external components as close as possible to
the op amp. Surface-mount components are an excel-
lent choice.
Although optimized for use as operational amplifiers,
the MAX4291/MAX4292/MAX4294 can also be used as
rail-to-rail I/O comparators. Typical propagation delay
depends on the input overdrive voltage, as shown in
Figure 8. External hysteresis can be used to minimize
the risk of output oscillation. The positive feedback cir-
cuit, shown in Figure 9, causes the input threshold to
change when the output voltage changes state. The
two thresholds create a hysteresis band that can be
calculated by the following equations:
Figure 7c. Pulse Response with Isolating Resistor (100 )
Using the MAX4291/MAX4292/MAX4294
OUT
Power-Supply Bypassing and Layout
IN
EE
V
CC
supplies should be bypassed to ground
= 2.4V, R
L =
2k TO V
10 s/div
ISO
EE
, C
L
= 1000pF, R
forms a voltage divider
as Comparators
ISO =
100
100mV
0
100mV
0
EE
(in this
CC
11