Rainbow Electronics MAX4165_MAX4169 User Manual

Page 10

MAX4165–MAX4169

High-Output-Drive, Precision, Low-Power, Single-
Supply, Rail-to-Rail I/O Op Amps with Shutdown

______________________________________________________________________________________

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:

= 1 / 2

C2)

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
switchover transition region, which occurs near V

/ 2,

has been extended to minimize the slight degradation
in common-mode rejection ratio caused by mismatch of
the input pairs.

= +3V

900k

= +3V

Ω

4.7k

0.1

INPUT

0.25Vp-p

Ω

100k

1/2 MAX4167
1/2 MAX4168

Figure 3. Dual MAX4167/MAX4168 Bridge Amplifier for
200mW at 3V

R3 = R1 R2

MAX4165
MAX4166
MAX4167
MAX4168
MAX4169

Figure 4. Reducing Offset Error Due to Bias Current
(Noninverting)

R3 = R1 R2

MAX4165
MAX4166
MAX4167
MAX4168
MAX4169

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