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MAX9812

Tiny, Low-Cost, Single/Dual-Input, Fixed-Gain Microphone Amplifiers with Integrated Bias

Maxim Integrated 

MAX9812/MAX9813

Tiny, Low-Cost, Single/Dual-Input, Fixed-Gain

Microphone Amplifiers with Integrated Bias

Pin Description

PIN

MAX9812L/ MAX9813L/

MAX9812H MAX9813H

1

3

2

2

3

1

4

8

5

7

6

—

—

6

—

5

—

4

NAME

FUNCTION

SHDN

Active-Low Shutdown Input. Connect SHDN to VCC for normal operation. Connect SHDN

to GND for shutdown. SHDN is a high-impedance input; do not leave unconnected.

GND Ground

OUT Amplifier Output

VCC Positive Supply. Bypass VCC to GND with a 0.1µF capacitor.

BIAS

Low-Noise Microphone Bias Output. 2.3V output for MAX9812L/MAX9813L. 4V output for

MAX9812H/MAX9813H.

IN Amplifier Input (MAX9812)

IN1 Amplifer Input 1 (MAX9813)

IN2 Amplifier Input 2 (MAX9813)

IN1/IN2 Input Selector. When IN1/IN2 is high, IN1 is selected. When IN1/IN2 low, IN2 is selected.

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.

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.

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.

Output Stage

The MAX9812_/MAX9813_ rail-to-rail output (OUT) typical-

ly swings to within 100mV of the rails when driving 10kΩ.

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 unconnected.

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.

Applications Information

Power-Up

The MAX9812_/MAX9813_ output typically settles to

95% within 10ms after power-up.

Typical Application Circuit

Figure 1 shows the MAX9813H used as a preamplifier

with the MAX9760 3W audio power amplifier.

Maxim Integrated

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