STCD2400F35F Datasheet, PDF (14/39 Pages) STMicroelectronics – Multichannel clock distribution circuit

Application information
4
Application information
STCD22x0, STCD23x0, STCD24x0
4.1
LDO input capacitor
A 1 µF input capacitor is required for the input of the LDO of the STCD22x0, STCD23x0 and
STCD24x0 (the amount of capacitance can be increased without limit). This capacitor must
be located as close as possible to the V_CC pin on the PC board and return to a clean analog
ground. Any good quality ceramic, tantalum or film capacitor can be used for this capacitor.
4.2
LDO output capacitor
A 1 µF external capacitor is required for the output VTCXO of the LDO of the STCD22x0,
STCD23x0 and STCD24x0. The STCD22x0, STCD23x0 and STCD24x0 are designed to
work with low ESR (equivalent series resistance) ceramic capacitors. Make sure the ESR is
lower than 500 mΩ to stabilize the VTCXO. Also, capacitor tolerance and variation with
temperature must be considered to assure the minimum amount of capacitance provided at
all times. This capacitor should be located as close as possible to the VTCXO pin on the PC
board.
4.3
LDO BYP pin
A 10 nF ceramic capacitor is required for the LDO BYP pin to ensure lower noise. Any good
quality ceramic, tantalum or film capacitor can be used. The capacitor should be located as
close as possible to the BYP pin on the PC board.
4.4
MC_REQ pin
In the STCD22x0, STCD23x0, and STCD24x0, the MC_REQ pin is open drain and active low.
Since MC_REQ is active low, if none of the clock output is required, the STCD22x0,
STCD23x0 and STCD24x0 are set to standby mode which turns off the internal LDO
VTCXO.
MC_REQ is designed as an open drain structure. A pull-up resistor (50 kΩ recommended) is
needed on the PC board to connect this pin to an external 1.8 V supply. Make sure the
current flowing through this pin is kept within 3 mA to guarantee the proper function of the
circuit.
If the MC_REQ function is not used in the application, the user can connect this pin to GND or
leave it unconnected. Other functions of the STCD2xx0 will not be affected.
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Doc ID 15400 Rev 2