MT88E45

Advance Information

2

Figure 2 - Pin Connections

Pin Description

Pin # Name

Description

Voltage Reference (Output). Nominally Vdd/2. It is used to bias the Tip/Ring and Hybrid input

op-amps.

2

IN1+

Tip/Ring Op-amp Non-inverting (Input).

3

IN1-

Tip/Ring Op-amp Inverting (Input).

4

GS1

Tip/Ring Gain Select (Output). This is the output of the Tip/Ring connection op-amp. The op-

amp should be used to connect the MT88E45 to Tip and Ring. The Tip/Ring signal can be

amplified or attenuated at GS1 via selection of the feedback resistor between GS1 and IN1-. FSK

demodulation (which is always on Tip/Ring) or CAS detection (for MEI or BT on-hook CLIP) of the

GS1 signal is enabled via the CB1 and CB2 pins. See Tables 1 and 2.

5

Vss

Power supply ground.

6

OSC1 Oscillator (Input). Crystal connection. This pin can also be driven directly from an external clock

source.

7

OSC2 Oscillator (Output). Crystal connection. When OSC1 is driven by an external clock, this pin

should be left open.

8

CB0

Control Bit 0 (CMOS Input). This pin is used primarily to select the 3-wire FSK data interface

mode. When it is low, interface mode 0 is selected where the FSK bit stream is output directly.

When it is high, interface mode 1 is selected where the FSK byte is stored in a 1 byte buffer which

can be read serially by the application’s microcontroller.

The FSK interface is consisted of the DATA, DCLK and DR/STD pins. See the 3 pin descriptions

to understand how CB0 affects the FSK interface.

When CB0 is high and CB1, CB2 are both low the MT88E45 is put into a power down state

consuming minimal power supply current. See Tables 1 and 2.

9

DCLK

3-wire FSK Interface Data Clock (Schmitt Input/CMOS Output). In mode 0 (when the CB0 pin

is logic low) this is a CMOS output which denotes the nominal mid-point of a FSK data bit.

In mode 1 (when the CB0 pin is logic high) this is a Schmitt trigger input used to shift the FSK data

byte out to the DATA pin.

1

2

3

4

5

6

9

10

20

19

18

17

16

15

14

13

IN1+

IN1-

GS1

Vss

OSC1

DCLK

DATA

IN2+

IN2-

GS2

CB2

CB1

Vdd

CD

ST/GT

MT88E45

7

OSC2

8

CB0

12

11

EST

DR/STD