BA338L Просмотр технического описания (PDF) - ROHM Semiconductor

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BA338L

Mute detector IC

ROHM Semiconductor 

Audio ICs

FApplication example

BA336 / BA338 / BA338L

FAttached components (see Fig. 3)

(1) Input coupling capacitor CIN and resistor RIN (Pin 3)

This capacitor is for coupling a pre-amp to the

BA336 / BA338 / BA338L.

If the DC level of the pre-amp output is GND, the coupling

capacitor can be omitted. If a coupling capacitor is con-

nected, Pin 3 must be connected to GND through a resis-

tor. If the resistor between Pin 3 and GND is too large, an

offset will occur due to a voltage drop caused by the input

current, and the input decision level will change. We rec-

ommend 10kΩ or less. The input decision level of the

BA336 / BA338 / BA338L is highly sensitive at*52dBm.

In the application example, the pre-stage output is di-

vided to adjust the sensitivity and increase the input im-

pedance. Furthermore, the low cutoff frequency fc is de-

termined by the input circuit time constant or the Pin 4

time constant, whichever is smaller. As it is better to de-

termine fc by the Pin 4 CF when the power is turned on,

we recommend making the time constant of the input cir-

cuit larger than that of Pin 4.

(2) DC cutoff capacitor in feedback circuit CF (Pin 4)

This determines the low cutoff frequency fC. The relation

of CF and fC is as follows :

1

CF =

(µF)

0.4πfC (kHz)

If CF = 1µF, fC 800Hz.

The larger CF is, the more time it will take for the circuit

730

to stabilize when the power is turned on.

(3) Muting capacitor for power up CM (Pin 6)

After the power is turned on, this capacitor stops song

selection until the circuit stabilizes. If the value of CF is

large, a large CM will also be necessary. CM must be

greater than CF. Also, if it takes longer for the external cir-

cuit to stabilize, select CM based on the external circuit.

The relation between CM and the muting time is as fol-

lows :

TM 30CM (µF)

(4) Noise filter capacitor CN (Pin 7)

This capacitor prevents errors due to pulse noise.

When an input signal is shorter than the time determined

by TN = CN (µF) ms (BA338 / BA338L) or TN = 20CN (µF)

ms (BA336), the IC will not respond and an output pulse

will not be generated. If pulse noise appears continuous-

ly at the input, the effectiveness of the noise filter will be

decreased. If it is likely that continuous noise will appear,

attach a discharge resistor RN between Pin 7 and GND

(RN y 30kΩ).

There are differences in the noise filter functions of the

BA336 and the BA338 / BA338L. Refer to the section,

“Differences between the noise filters of the BA336 and

BA338 / BA338L”.

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