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MC145540

ADPCM Codec

Motorola => Freescale 

2.4.2 Analog Interface Pins

TG

Transmit Gain (Pin 1)

This is the output of the transmit gain setting operational amplifier and the input to the transmit band-

pass filter. This op amp is capable of driving a 2 kΩ load to the VAG pin. When TI – and TI+ are connected

to VDD, the TG op amp is powered down and the TG pin becomes a high-impedance input to the trans-

mit filter. All signals at this pin are referenced to the VAG pin. This pin is high impedance when the device

is in the analog power-down mode. This op amp is powered by the VDD pin.

TI –

Transmit Analog Input (Inverting) (Pin 2)

This is the inverting input of the transmit gain setting operational amplifier. Gain setting resistors are

usually connected from this pin to TG and from this pin to the analog signal source. The common mode

range of the TI + and TI– pins is from 1.0 V, to VDD – 2 V. Connecting this pin and TI + (pin 3) to VDD will

place this amplifier’s output (TG) in a high-impedance state, thus allowing the TG pin to serve as a

high-impedance input to the transmit filter.

TI+

Transmit Analog Input (Non-Inverting) (Pin 3)

This is the non-inverting input of the transmit input gain setting operational amplifier. This pin accommo-

dates a differential to single ended circuit for the input gain setting op amp. This allows input signals that

are referenced to the VSS pin to be level shifted to the VAG pin with minimum noise. This pin may be

connected to the VAG pin for an inverting amplifier configuration if the input signal is already referenced

to the VAG pin. The common mode range of the TI+ and TI – pins is from 1.0 V, to VDD – 2 V. Connecting

this pin and TI – (pin 2) to VDD will place this amplifier’s output (TG) in a high-impedance state, thus

allowing the TG pin to serve as a high-impedance input to the transmit filter.

RO

Receive Analog Output (Pin 5)

This is the non-inverting output of the receive smoothing filter from the digital-to-analog converter. This

output is capable of driving a 2 kΩ load to 1.575 V peak referenced to the VAG pin. This pin may be dc

referenced to either the VAG pin or a voltage of half of VEXT by BR2 (b7). This pin is high impedance

when the device is in the analog power-down mode. This pin is high impedance except when it is en-

abled for analog signal output.

AXO –

Auxiliary Audio Power Output (Inverting) (Pin 6)

This is the inverting output of the auxiliary power output drivers. The Auxiliary Power Driver is capable of

differentially driving a 300 Ω load. This power amplifier is powered from VEXT and its output can swing to

within 0.5 V of VSS and VEXT. This pin may be dc referenced to either the VAG pin or a voltage of half of

VEXT by BR2 (b7). This pin is high impedance in power down. This pin is high impedance except when it

is enabled for analog signal output.

AXO +

Auxiliary Audio Power Output (Non-Inverting) (Pin 7)

This is the non-inverting output of the auxiliary power output drivers. The Auxiliary Power Driver is

capable of differentially driving a 300 Ω load. This power amplifier is powered from VEXT and its output

can swing to within 0.5 V of VSS and VEXT. This pin may be dc referenced to either the VAG pin or a

voltage of half of VEXT by BR2 (b7). This pin is high impedance in power down. This pin is high imped-

ance except when it is enabled for analog signal output.

PI

Power Amplifier Input (Pin 10)

This is the inverting input to the PO– amplifier. The non-inverting input to the PO – amplifier may be dc

referenced to either the VAG pin or a voltage of half of VEXT by BR2 (b7). The PI and PO – pins are used

with external resistors in an inverting op amp gain circuit to set the gain of the PO + and PO – push-pull

2-12

MC145540

MOTOROLA

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