STCD2400 Datasheet, PDF (17/39 Pages) STMicroelectronics – Multichannel clock distribution circuit

STCD22x0, STCD23x0, STCD24x0
Application information
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.
In 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.
In 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.
In Figure 9 and 10, all the output clock enables are active high since both OPT1 and OPT2
are connected to V_CC.
Figure 9. Typical application circuit using STCD24x0 for RF ends of TD-
SCDMA/GSM dual-mode mobile phone
V_CC
C
C
VDD
XO
EN
C
STCD24x0
BYP
VIO ^VTCXO
EN4
CLK4
EN3
CLK3
MC_REQ
EN2
MCLK
V_CC
CLK2
OPT1
EN1
OPT2
CLK1
GND
Mode
Selection
TD-SCDMA
Transmitter
TD-SCDMA
Receiver
GSM
Transceiver
ai14022
Doc ID 15400 Rev 2
17/39