BL34018
additionally controls the attack and decay time of this circuit. The gain control loop limits
the speaker amp input to prevent clipping at SKO. The internal resistance at the AGC pin
is nominally 110 k ohms.
18
CS
Digital chip select input. When at a logic “0” (<0.7 V) the VCC regulator is enabled.
When at a logic “1” (>1.6 V), the chip is in the standby mode drawing 0.5 mA. An open
CS
pin is a logic “0”. Input impedance is nominally 140 k ohms. The input voltage
should not exceed 11 V.
19
20
SKI
VCC
Input to the speaker amplifier. Input impedance is normally 20 k ohms.
A 5.4 V regulated output which powers all circuits except the speaker amplifier output
stage. VCC can be used to power external circuitry such as a microprocessor( 3.0 mA
max). A filter capacitor is required. The BL34018 can be powered by a separate regulated
supply by connecting V+ and VCC to a voltage between 4.5 V and 6.5 V while
maintaining
CS
at a logic “1”.
21
VB
An output voltage equal to approximately VCC/2 which serves as an analog ground for
the speakerphone system. Up to 1.5 mA of external load current may be sourced from VB.
Output impedance is 250 ohms. A filter capacitor is required.
Ground pin for the IC (except the speaker amplifier).
Gnd
22
23
XDC
Transmit detector output. A resistor and capacitor at this pin hold the system in the
transmit mode during pauses between words and phrases. When the XDC pin voltage
decays to ground the attenuators switch from the transmit mode to the idle mode. The
internal resistor at XDC is nominally 2.6 k ohms.
Volume control input. Connecting this pin to the slider of a variable resistor provides
receive mode volume control. The VLC pin voltage should be less than or equal to VB.
Attenuator control filter. A capacitor connected to this pin reduces noise transients as the
attenuator control switches levels of attenuation.
Output of the receive attenuator. Normally this pin is ac coupled to the input of the
speaker amplifier.
Input of the receive attenuator. Input impedance is nominally 5.0 k ohms.
A resistor to ground determines the nominal gain of the receive attenuator. The receive
channel gain is directly proportional to the RRX resistance.
24
VLC
25
ACF
26
27
28
RXO
RXI
RRX
http://www.belling.com.cn
-3-
Total
16 Pages
8/15/2006
Wrote by 2006
BELLING [ SHANGHAI BELLING CO., LTD. ]
