ISD2540 datasheet(7/42 Pages) WINBOND

7 / 42 page

ISD2532/40/48/64

PIN NO.

PIN NAME

SOIC/

PDIP

TSOP

FUNCTION

VCCA, VCCD

16, 28

23, 7

Supply Voltage: To minimize noise, the analog and digital circuits

in the ISD2500 series devices use separate power busses. These

voltage busses are brought out to separate pins and should be tied

together as close to the supply as possible. In addition, these

supplies should be decoupled as close to the package as possible.

MIC

Microphone: The microphone pin transfers input signal to the on-

chip preamplifier. A built-in Automatic Gain Control (AGC) circuit

controls the gain of this preamplifier from –15 to 24dB. An external

microphone should be AC coupled to this pin via a series capacitor.

The capacitor value, together with the internal 10 KΩ resistance on

this pin, determines the low-frequency cutoff for the ISD2500 series

passband. See Winbond’s Application Information for additional

information on low-frequency cutoff calculation.

MIC REF

Microphone Reference: The MIC REF input is the inverting input

to the microphone preamplifier. This provides a noise-canceling or

common-mode rejection input to the device when connected to a

differential microphone.

AGC

Automatic Gain Control: The AGC dynamically adjusts the gain of

the preamplifier to compensate for the wide range of microphone

input levels. The AGC allows the full range of whispers to loud

sounds to be recorded with minimal distortion. The “attack” time is

determined by the time constant of a 5 KΩ internal resistance and

an external capacitor (C2 on the schematic of Figure 5 in section

11) connected from the AGC pin to VSSA analog ground. The

“release” time is determined by the time constant of an external

resistor (R2) and an external capacitor (C2) connected in parallel

between the AGC pin and VSSA analog ground. Nominal values of

470 KΩ and 4.7 µF give satisfactory results in most cases.

ANA IN

Analog Input: The analog input transfers analog signal to the chip

for recording. For microphone inputs, the ANA OUT pin should be

connected via an external capacitor to the ANA IN pin. This

capacitor value, together with the 3.0 KΩ input impedance of ANA

IN, is selected to give additional cutoff at the low-frequency end of

the voice passband. If the desired input is derived from a source

other than a microphone, the signal can be fed, capacitively

coupled, into the ANA IN pin directly.

Publication Release Date: June 2003

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