the amount of desired gain, keeping in mind the maxi-

mum output amplitude. The output coupling capacitor,

put, preventing DC current flowing to the load. The out-

put capacitor and the load impedance form a highpass

filer with the -3dB point determined by:

For a 32

Ω load, a 100µF aluminum electrolytic capaci-

tor gives a low-frequency pole at 50Hz.

Bridge Amplifier

The circuit shown in Figure 3 uses a dual MAX4230 to

implement a 3V, 200mW amplifier suitable for use in

size-constrained applications. This configuration elimi-

nates the need for the large coupling capacitor

required by the single op-amp speaker driver when sin-

gle-supply operation is necessary. Voltage gain is set

to 10V/V; however, it can be changed by adjusting the

82k

Ω resistor value.

Rail-to-Rail Input Stage

The MAX4230–MAX4234 CMOS op amps have parallel-

connected N- and P-channel differential input stages

that combine to accept a common-mode range extend-

ing to both supply rails. The N-channel stage is active

for common-mode input voltages typically greater than

1.2V).

Rail-to-Rail Output Stage

The minimum output is within millivolts of ground for sin-

gle-supply operation, where the load is referenced to

and the output voltage swing of a MAX4230 connected

as a voltage follower. The maximum output voltage

swing is load dependent; however, it is guaranteed to

with maximum load (32

Ω to ground).

The MAX4230–MAX4234 incorporate a smart short-cir-

output current, therefore protecting the device and the

is not activated. When the smart short circuit is not

active, the output currents can exceed 200mA (see

Typical Operating Characteristics.)

Input Capacitance

One consequence of the parallel-connected differential

input stages for rail-to-rail operation is a relatively large

at frequency (2

nation of the gain-setting resistors for the inverting or

noninverting amplifier configuration (Figure 5). If the pole

frequency is less than or comparable to the unity-gain

bandwidth (10MHz), the phase margin is reduced, and

the amplifier exhibits degraded AC performance through

either ringing in the step response or sustained oscilla-

tions. The pole frequency is 10MHz when R

′ = 2kΩ. To

maximize stability, R

′ << 2kΩ is recommended.

f

RC

dB

L OUT

−

=

3

1

2

π

High-Output-Drive, 10MHz, 10V/µs,

Rail-to-Rail I/O Op Amps with Shutdown in SC70

10

______________________________________________________________________________________

Figure 4. Rail-to-Rail Input/Output Range

Figure 3. Dual MAX4230/MAX4231 Bridge Amplifier for 200mW

at 3V

1

6

7

5

2

8

3V

3V

3

4

MAX4232

1/2

MAX4232

1/2

R5

51k

Ω

R1

16k

Ω

R2

82k

Ω

R4

10k

Ω

32

Ω

fs = 100Hz

R3

10k

Ω

R6

51k

Ω

C2

0.1

µF

C1

0.1

µF

IN

(1V/div)

OUT

(1V/div)

5

µs/div

Ω