INMP421

The DATA signal does not need to be buffered in normal use when the INMP421 microphones are placed close to the codec on the

PCB. If the INMP421 must drive the DATA signal over a long cable (>15 cm) or other large capacitive load, a digital buffer may be

needed. Use a signal buffer on the DATA line only when one microphone is in use or after the point where two microphones are

connected (see Figure 12.)

Figure 12. Buffered Connection Between Stereo INMP421 Devices and a Codec

The DATA output of each microphone in a stereo configuration cannot be individually buffered because the two buffer outputs

cannot drive a single signal line. If a buffer is used, take care to select a buffer with low propagation delay so that the timing of the

data connected to the codec is not corrupted.

When long wires are used to connect the codec to the INMP421, a 100 Ω source termination resistor can be used on the clock output

of the codec instead of a buffer to minimize signal over-shoot or ringing. Depending on the drive capability of the codec clock output,

a buffer may still be needed, as shown in Figure 13.

SLEEP MODE

The microphone enters sleep mode when the clock is turned off or the clock frequency falls below 1 kHz. In sleep mode, the

microphone data output is in high impedance state and the current consumption is less than 50 µA.

POWER SAVINGS WHEN DISABLING ONE MICROPHONE IN A MULTIMICROPHONE APPLICATION

The INMP421 has a unique power-saving feature when used in systems where two or more microphones share the same clock

and/or data lines. The microphone is designed to present high impedance on both the clock and data pins when the power supply

CLOCK OUTPUT

CODEC

DATA

INMP421

INMP421

CLK

DATA INPUT

DATA

CLK

Page 14 of 21

Document Number: DS-INMP421-00

Revision: 1.0.