M41T00AUD_12 STMICROELECTRONICS [STMicroelectronics], M41T00AUD_12 Datasheet - Page 28

• Manufacturer Part Number: M41T00AUD_12
• Description: Serial real-time clock (RTC) with audio
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Audio section operation
7
Figure 16. Audio section diagram
28/42
R1 x
S IN
Sum multiple audio
signals through external
resistors, but single input
Set R1’s to 2x R2 for unity gain
be a minimum
R2 should
Audio section operation
The audio section is comprised of five main parts. The input includes a summing amplifier.
A minimum 10 kΩ feedback resistor is required. With that and 20 kΩ input resistors, the
input signals will be summed at unity gain.
An audio switch follows the amplifier. A tone, selectable between 256 and 512 Hz, can be
inserted into the audio stream in lieu of the input amplifier's output.
A low pass filter is next with a cut off of 8 kHz. To get a band pass with a 100 Hz low end,
the user should place an appropriate coupling capacitor at the input pin.
RTC timing chain
FBK
AIN
From internal
V DD
2
V DD
256 Hz
512 Hz
SELECT
256/512
register bits
Doc ID 13480 Rev 5
ON/OFF
TONE
Low end of band pass filter is actually
implemented by blocking capacitor at
input pin. Only the high end (low-pass
section) is implemented at this point in the
audio section.
100 Hz - 8 kHz
Switch 256/512 signal
in place of audio signal
BPF
GAIN, 3 dB steps,
–33 dB to +12 dB
(4-bit register)
V BIAS
V DD
2
1 µF
M41T00AUD
AOUT+
AOUT–
300 mW
ai13328