STCD22X0 datasheet(14/39 Pages) STMICROELECTRONICS

14 / 39 page

Application information

STCD22x0, STCD23x0, STCD24x0

14/39

Doc ID 15400 Rev 2

Application information

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 VCC 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 m

Ω 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

MCREQ pin

In the STCD22x0, STCD23x0, and STCD24x0, the MCREQ pin is open drain and active low.

Since MCREQ 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.

MCREQ 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 MCREQ 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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