MAX4063 MAXIM [Maxim Integrated Products], MAX4063 Datasheet - Page 10

• Manufacturer Part Number: MAX4063
• Description: Differential Microphone Preamplifier with Internal Bias and Complete Shutdown
• Manufacturer: MAXIM [Maxim Integrated Products]

Input voltages should be sufficiently small such that the
output is not clipped in either differential or common-
mode application. The topology used in the MAX4063
means that the CMRR actually improves at higher dif-
ferential gains—another advantage of using differential
sensing.
The auxiliary input is a single-ended input intended to
be used with a jack-socket type microphone input
(Figure 1). Internal DC-bias components (as on the
main inputs) allow the input signal to be AC-coupled.
Mechanically switched jack sockets can be used in
conjunction with the INT/AUX select pin, allowing the
auxiliary microphone input to be automatically selected
when a jack socket is inserted.
On the MAX4063 thin QFN package, connect the
exposed paddle (backside of PRS) to the ground
plane. The MAX4063 has an integrated low-noise, low-
output impedance bias voltage. An optimum electret
bias resistor can be set externally. This gives a low-
noise, flexible solution that can run from 2.4V to 5.5V,
which is suitable for hand-held devices such as PDAs
that typically have audio power supplies in the 3V
region (Figure 2).
In shutdown mode, the bias voltage is disabled. OUT
and OUT have a low-noise, DC-bias voltage indepen-
dent of the power supplies, resulting in superior PSRR
performance. The MAX4063 outputs are high imped-
ance when the part is in shutdown mode.
The MAX4063 features a differential output stage (OUT
and OUT), allowing optimum performance when con-
nected to ADCs and CODECs with differential inputs.
This differential output is particularly useful in designs
where the microphone preamplifier is mounted some
distance away from the CODEC/ADC, as the low-imped-
ance, differential line provides excellent noise rejection
and immunity (Figure 4).
Differential Microphone Preamplifier with
Internal Bias and Complete Shutdown
10
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Microphone Bias Voltage
Differential Output
Auxiliary Input
Output
DC Bias
The MAX4063 features a low-power, complete shut-
down mode. When SHDN goes low, the supply current
drops to 0.3µA, the output enters a high-impedance
state, and the bias current to the microphone is
switched off. Driving SHDN high enables the amplifier.
SHDN should not be left floating.
The MAX4063 operates from a 2.4V to 5.5V single sup-
ply. Bypass the power supply with a 0.1µF capacitor to
ground. In systems where analog and digital grounds
are available, the MAX4063 should be connected to the
analog ground.
Figure 2. MAX4063 Used for Biasing a Microphone
MICROPHONE
INPUT
V
CC
Applications Information
12
10
5
3
9
Power Supplies and Layout
BIAS
SHDN
AUX_IN
IN+
IN-
V
BIAS
14
SHDN
G1
2.4V TO 5.5V
6
MAX4063
G2
1
V
CC
Shutdown Mode
GND
INT/AUX 2
11
ADJ
OUT 8
OUT 4
7