Single/Dual/Quad, Low-Cost, SOT23,

Micropower, Rail-to-Rail I/O Op Amps

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11

For example, a MAX4040 running from a single +2.4V

Ω

The same application can drive a 4.6k

Ω load resistor

Driving Capacitive Loads

The MAX4040–MAX4044 are unity-gain stable for loads

up to 200pF (see Load Resistor vs. Capacitive Load

graph

in

Typical Operating Characteristics ).

Applications that require greater capacitive drive capa-

bility should use an isolation resistor between the output

and the capacitive load (Figures 6a–6c). Note that this

alternative results in a loss of gain accuracy because

Power-Supply Bypassing and Layout

The MAX4040–MAX4044 family operates from either a

single +2.4V to +5.5V supply or dual ±1.2V to ±2.75V

supplies. For single-supply operation, bypass the

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 by placing exter-

nal components as close as possible to the op amp.

Surface-mount components are an excellent choice.

Using the MAX4040–MAX4044

as Comparators

Although optimized for use as operational amplifiers,

the MAX4040–MAX4044 can also be used as rail-to-rail

I/O comparators. Typical propagation delay depends

on the input overdrive voltage, as shown in Figure 7.

External hysteresis can be used to minimize the risk of

output oscillation. The positive feedback circuit, shown

in Figure 8, 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:

R

=

2.4V - 0.1V

240 A

9.6k

to V

L

EE

µ

=

Ω

50mV/div

IN

OUT

50mV/div

MAX4040/42/44 fig06b

100

µs/div

Figure 6b. Pulse Response without Isolating Resistor

50mV/div

IN

OUT

50mV/div

MAX4040/42/44 fig06c

100

µs/div

Figure 6c. Pulse Response with Isolating Resistor

MAX4040–

MAX4044

≈ 1

Figure 6a. Using a Resistor to Isolate a Capacitive Load from

the Op Amp