Tiny, Low-Cost, Single/Dual-Input, Fixed-Gain
Microphone Amplifiers with Integrated Bias
Pin Description
PIN
MAX9812L/
MAX9812H
1
2
3
4
5
6
—
—
—
MAX9813L/
MAX9813H
3
2
1
8
7
—
6
5
4
NAME
FUNCTION
Active-Low Shutdown Input. Connect
SHDN
to V
CC
for normal operation. Connect
SHDN
to GND for shutdown.
SHDN
is a high-impedance input; do not leave floating.
Ground
Amplifier Output
Positive Supply. Bypass V
CC
to GND with a 0.1µF capacitor.
Low-Noise Microphone Bias Output. 2.3V output for MAX9812L/MAX9813L. 4V output for
MAX9812H/MAX9813H.
Amplifier Input (MAX9812)
Amplifer Input 1 (MAX9813)
Amplifier Input 2 (MAX9813)
Input Selector. When IN1/IN2 is high, IN1 is selected. When IN1/IN2 low, IN2 is selected.
MAX9812/MAX9813
SHDN
GND
OUT
V
CC
BIAS
IN
IN1
IN2
IN1/IN2
Detailed Description
The MAX9812_/MAX9813_ are low-power fixed-gain
microphone amplifiers available in a single- or dual-
input configuration. The gain is set at 10V/V (20dB) with
a 400kHz, -3dB bandwidth. They also feature a low-
noise, integrated microphone input bias voltage.
The output DC bias point is set to 1.5V for the MAX9812L/
MAX9813L and 2.5V for the MAX9812H/MAX9813H.
Shutdown Mode
SHDN
controls whether the MAX9812_/MAX9813_ is
active or in shutdown mode. Driving
SHDN
low forces a
low-power (100nA) shutdown mode. In this mode, the
OUT pin is set to a high-impedance state and the BIAS
pin is pulled down (70kΩ). Driving
SHDN
high enables
the MAX9812_/MAX9813_.
SHDN
is a high-impedance
input and cannot be left floating.
Single/Dual Input
The MAX9812L/MAX9812H are single-input amplifiers
and the MAX9813L/MAX9813H are dual-input ampli-
fiers. All devices typically have an input impedance of
85kΩ. The inputs to the dual version are controlled
through a fast 2:1 mux, selectable through the IN1/IN2
pin. Driving IN1/IN2 high selects IN1 and driving the
IN1/IN2 low selects IN2. IN1/IN2 is designed to be dri-
ven by a logic high of
≥2V
and a logic low
≤0.8V.
The IN1/IN2 has a 10µs switching time from one
channel to the other.
Driving Capacitive Loads
The MAX9812_/MAX9813_ output can drive up to 50pF
of capacitance without sustained oscillations.
Thermal Shutdown
The thermal shutdown feature protects the
MAX9812_/MAX9813_ from destruction due to overheat-
ing caused by shorting the outputs. This protection fea-
ture causes OUT and BIAS to shut down and go high
impedance when the die temperature reaches +140°C.
The device restarts after the die temperature falls below
+120°C.
PC2001 Low-Noise Microphone BIAS
The MAX9812_/MAX9813_ provide a low-noise voltage
BIAS designed for biasing electret condenser micro-
phone (ECM) cartridges. The BIAS output is regulated
to typically 2.3V for the MAX9812L/MAX9813L and 4V
for the MAX9812H/MAX9813H. In the single-input ver-
sion (MAX9812_), the BIAS output can source up to
1mA. In the dual-input version (MAX9813_), the BIAS
output can source up to 2mA. The MAX9812H/
MAX9813H provides a PC2001-compliant BIAS voltage.
Applications Information
Power-Up
The MAX9812_/MAX9813_ output typically settles to
95% within 10ms after power-up.
Output Stage
The MAX9812_/MAX9813_ rail-to-rail output (OUT) typical-
ly swings to within 100mV of the rails when driving 10kΩ.
Typical Application Circuit
Figure 1 shows the MAX9813H used as a preamplifier
with the MAX9760 3W audio power amplifier.
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DALLAS [ DALLAS SEMICONDUCTOR ]
