Datasheet

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SBOS365D − JUNE 2006 − REVISED JUNE 2009
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9
Figure 2 shows a single-supply, electret microphone
application where V
CM
is provided by a resistive divider.
The divider also provides the bias voltage for the elec-
tret element.
INPUT AND ESD PROTECTION
The OPA365 incorporates internal electrostatic dis-
charge (ESD) protection circuits on all pins. In the case
of input and output pins, this protection primarily con-
sists of current steering diodes connected between the
input and power-supply pins. These ESD protection
diodes also provide in-circuit, input overdrive protec-
tion, provided that the current is limited to 10mA as
stated in the Absolute Maximum Ratings. Figure 3
shows how a series input resistor may be added to the
driven input to limit the input current. The added resistor
contributes thermal noise at the amplifier input and its
value should be kept to the minimum in noise-sensitive
applications.
RAIL-TO-RAIL INPUT
The OPA365 product family features true rail-to-rail in-
put operation, with supply voltages as low as ±1.1V
(2.2V). A unique zer∅-crossover input topology elimi-
nates the input offset transition region typical of many
rail-to-rail, complementary stage operational amplifiers.
This topology also allows the OPA365 to provide superi-
or common-mode performance over the entire input
range, which extends 100mV beyond both power-sup-
ply rails, as shown in Figure 4. When driving ADCs, the
highly linear V
CM
range of the OPA365 assures that the
op amp/ADC system linearity performance is not com-
promised.
3.3V
49k
Ω
V
OUT
OPA365
Clean 3.3V Supply
1
µ
F
4k
Ω
6k
Ω
Electret
Microphone
5k
Ω
Figure 2. Microphone Preamplifier
5k
Ω
OPA365
10mA max
V+
V
IN
V
OUT
I
OVERLOAD
Figure 3. Input Current Protection
OFFSET VOLTAGE vs COMMON−MODE VOLTAGE
V
OS
(
µ
V)
200
150
100
50
0
−
50
−
150
−
100
−
200
−
2
−
3
Common−Mode Voltage (V)
3
−
10 1 2
V
S
=
±
2.75V
OPA365
Competitors
Figure 4. OPA365 has Linear Offset Over the
Entire Common-Mode Range