STCD22X0 datasheet(17/39 Pages) STMICROELECTRONICS

17 / 39 page

STCD22x0, STCD23x0, STCD24x0

Application information

Doc ID 15400 Rev 2

17/39

4.8

Typical application connections

The STCD2400 clock distribution circuit requires a source clock input as the reference clock

(for example, XO). At most 4 devices can be connected to the outputs. The typical

application circuit using STCD2400 is shown in

Figure 9 and 10 . The MC

REQ is open drain

output and active low. A pull-up resistor is needed to connect to an external 1.8 V supply

VIO. If the clock source enable is active high, the user can use VTCXO as the master clock

enable control signal, please refer to

Figure 4 for the detailed connection.

Figure 9, the clock from XO is distributed to the TD-SCDMA transmitter and receiver and

GSM transceiver separately to be used as reference clocks.

Figure 10, the buffer #4 output is fed into the Bluetooth system. In order to allow minimum

power consumption, a Bluetooth system always has a clock request feature. If the Bluetooth

system does not require the clock, the clock request disables the clock output. The enable

pins can also be connected to an external 1.8 V supply to force the buffer to always be on.

Figure 9 and 10, all the output clock enables are active high since both OPT1 and OPT2

are connected to VCC.

Figure 9.

Typical application circuit using STCD24x0 for RF ends of TD-

SCDMA/GSM dual-mode mobile phone

STCD24x0

VCC

MCREQ

VTCXO

MCLK

EN1

EN2

GND

BYP

CLK1

CLK2

EN3

CLK3

EN4

CLK4

VIO

GSM

Transceiver

TD-SCDMA

Receiver

TD-SCDMA

Transmitter

Mode

Selection

OPT1

OPT2

VCC

ai14022

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