High-Output-Drive, Precision, Low-Power, Single-

Supply, Rail-to-Rail I/O Op Amps with Shutdown

10

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Single-Supply Speaker Driver

The MAX4165/MAX4166 can be used as a single-sup-

ply speaker driver, as shown in the

Typical Operating

Circuit. Capacitor C1 is used for blocking DC (a 0.1µF

ceramic capacitor can be used). When choosing resis-

tors R3 and R4, take into consideration the input bias

current as well as how much supply current can be tol-

erated. Choose resistors R1 and R2 according to the

amount of gain and current desired. Capacitor C3

ensures unity gain for DC. A 10µF electrolytic capacitor

is suitable for most applications. The coupling capaci-

tor C2 sets a low-frequency pole and is fairly large in

value. For a 32

Ω load, a 100µF coupling capacitor

gives a low-frequency pole at 50Hz. The low-frequency

pole can be set according to the following equation:

Bridge Amplifier

The circuit shown in Figure 3 uses a dual MAX4167/

MAX4168 to implement a 3V, 200mW amplifier suitable

for use in size-constrained applications. This configura-

tion eliminates the need for the large coupling capaci-

tor required by the single op-amp speaker driver when

single-supply operation is a must. Voltage gain is set to

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

900k

Ω resistor value. DC voltage at the speaker is limit-

ed to 10mV. The 47

Ω and 0.1µF capacitors across the

speaker maintain a low impedance at the load as fre-

quency increases.

Rail-to-Rail Input Stage

Devices in the MAX4165–MAX4169 family of high-out-

put-current amplifiers have rail-to-rail input and output

stages designed for low-voltage, single-supply opera-

tion. The input stage consists of separate NPN and

PNP differential stages that combine to provide an

input common-mode range that extends 0.25V beyond

the supply rails. The PNP stage is active for input volt-

ages close to the negative rail, and the NPN stage is

active for input voltages near the positive rail. The

has been extended to minimize the slight degradation

in common-mode rejection ratio caused by mismatch of

the input pairs.

900k

47

Ω

4.7k

4.7k

0.1

µF

1

µF

0.1

µF

INPUT

0.25Vp-p

32

Ω

100k

100k

100k

100k

100k

100k

1/2 MAX4167

1/2 MAX4168

1/2 MAX4167

1/2 MAX4168

Figure 3. Dual MAX4167/MAX4168 Bridge Amplifier for

200mW at 3V

R3

R3 = R1

R2

R1

R2

MAX4165

MAX4166

MAX4167

MAX4168

MAX4169

Figure 4. Reducing Offset Error Due to Bias Current

(Noninverting)

R3

R3 = R1

R2

R1

R2

MAX4165

MAX4166

MAX4167

MAX4168

MAX4169

Figure 5. Reducing Offset Error Due to Bias Current (Inverting)