MT88L85AP Ver la hoja de datos (PDF) - Mitel Networks

Número de pieza

componentes Descripción

Fabricante

MT88L85AP

3V Integrated DTMF Transceiver with Power Down & Adaptive Micro Interface

Mitel Networks 

Advance Information

MT88L85

Pin Description

Pin #

24 28

Name

8,9 3,5, NC No Connection.

17

10,11

16,

20,

25

Functional Description

Description

Receiver Section

The MT88L85 Integrated DTMF Transceiver consists

of a high performance DTMF receiver with an

internal gain setting amplifier and a DTMF generator,

which employs a burst counter to synthesize precise

tone bursts and pauses. A call progress mode can

be selected so that frequencies within the specified

passband can be detected. The adaptive micro

interface allows microcontrollers, such as the

68HC11, 80C51 and TMS370C50, to access the

MT88L85 internal registers.

Power Down

The MT88L85 provides enhanced power down

functionality to facilitate minimization of supply

current consumption. DTMF transmitter and receiver

circuit blocks may be independently powered down

via register control. When asserted, the RxEN

control bit powers down all analog and digital

circuitry associated solely with the DTMF and Call

Progress receiver. The TOUT control bit is used to

disable the transmitter and put all circuitry

associated only with the DTMF transmitter in power

down mode. With the TOUT control bit asserted, the

TONE output pin is held in a high impedance

(floating) state. When both power down control bits

are asserted, circuits utilized by both the DTMF

transmitter and receiver are also powered down.

This includes the crystal oscillators, and the VRef

generator. In addition, the IRQ , TONE output and

DATA pins are held in a high impedance state.

Finally, the whole device is put in a power down state

when the PWDN pin is asserted.

Input Configuration

The input arrangement of the MT88L85 provides a

differential-input operational amplifier as well as a

bias source (VRef), which is used to bias the inputs at

VDD/2. Provision is made for connection of a

feedback resistor to the op-amp output (GS) for gain

adjustment. In a single-ended configuration, the

input pins are connected as shown in Figure 3.

Figure 4 shows the necessary connections for a

differential input configuration.

Separation of the low and high group tones is

achieved by applying the DTMF signal to the inputs

of two sixth-order switched capacitor bandpass

filters, the bandwidths of which correspond to the low

and high group frequencies (see Table 1). The filters

also incorporate notches at 350 Hz and 440 Hz for

exceptional dial tone rejection. Each filter output is

followed by a single order switched capacitor filter

section, which smooths the signals prior to limiting.

Limiting is performed by high-gain comparators

which are provided with hysteresis to prevent

detection of unwanted low-level signals. The outputs

of the comparators provide full rail logic swings at

the frequencies of the incoming DTMF signals.

MT88L85

IN+

C

RIN

IN-

VOLTAGE GAIN

(AV) = RF / RIN

RF

GS

VRef

Figure 3 - Single-Ended Input Configuration

C1

R1

MT88L85

IN+

C2

R4

R3

IN-

R5

GS

R2

VRef

DIFFERENTIAL INPUT AMPLIFIER

C1 = C2 = 10 nF

R1 = R4 = R5 = 100 kΩ

R2 = 60kΩ, R3 = 37.5 kΩ

R3 = (R2R5)/(R2 + R5)

VOLTAGE GAIN

(AV diff) - R5/R1

INPUT IMPEDANCE

(ZINdiff) = 2 R12 + (1/ωC)2

Figure 4 - Differential Input Configuration

4-73

Share Link: