Figure 15. Buffered Connections Between Stereo INMP621s and a Codec
When long wires are used to connect the codec to the INMP621, a source termination resistor can be used on the clock output of the
codec instead of a buffer to minimize signal overshoot or ringing. Match the value of this resistor to the characteristic impedance of
the CLK trace on the PCB. Depending on the drive capability of the codec clock output, a buffer may still be needed, as shown in Figure
15
.
SLEEP MODE
The microphone enters sleep mode when the clock frequency falls below 1 kHz. In this mode, the microphone data output is in a high
impedance state. The current consumption in sleep mode is less than 5.5 µA.
The INMP621 enters sleep mode within 1ms of the clock frequency falling below 1 kHz. The microphone wakes up from sleep mode
and begins to output data 32,768 cycles after the clock becomes active. For a 3.072 MHz clock, the microphone starts to output data in
10.7 ms. For a 2.4 MHz clock, the microphone starts to output data in 13.7 ms. The wake-up time, as specified in Table 2, indicates the
time from when the clock is enabled to when the INMP621 outputs data within 3 dB of its settled sensitivity.
START-UP TIME
The start-up time of the INMP621 from when the clock is active is the same as the wake-up time. The microphone starts up 32,768
cycles after the clock is active.
Page 14 of 21
Document Number: DS-INMP621-00
Revision: 1.1
Rev Date: 05/21/2014
