CY22391 查看數據表（PDF） - Cypress Semiconductor

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CY22391

Factory Programmable Quad PLL Clock Generator with VCXO

Cypress Semiconductor 

CY22388/89/91

Analog VCXO

There are three programmable reference operating modes for

the CY22388/89/91 family of devices. The first mode utilizes

an external pullable crystal and incorporates an internal

Analog VCXO.

The second mode configures the internal crystal oscillator to

accept an external driven reference source from 1 to 100 MHz.

The input capacitance on the XIN PIN when driven in this

mode is 15 pF.

The third mode disables the VCXO input control and sets the

internal oscillator to a fixed frequency operation. The load

capacitance seen by the external crystal when connected to

PINS XIN and XOUT is equal to 12 pF.

One of the key components to the CY22388/89/91 family of

devicesistheanalogVCXO.TheVCXO isusedto“pull”the

reference crystal higher or lower in order to lock the system

frequency to an external source. This is ideal for applications

where the output frequency needs to track along with an

external reference frequency that is constantly shifting.

The VCXO is completely analog, so there is infinite resolution

on the VCXO pull curve. The Analog to Digital Converter steps

that are normally associated with a digital VCXO input is not

present in this device. A special pullable crystal must be used

to in order to have adequate VCXO pull range. Pullable Crystal

specifications are included in this data sheet.

Please refer to the CY22388/89/91 Application Note for

pullable crystal recommendations outside of the standard

industry frequencies given in the Pullable Crystal Specifica-

tions.

VCXO Profile

Figure 2 shows an example of what a VCXO profile looks like.

The analog voltage input is on the X-axis and the PPM range

is on the Y-axis. An increase in the VCXO input voltage results

in a corresponding increase in the output frequency. This has

the effect of moving the PPM from a negative to positive offset.

Figure 2. VCXO Profile

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200

150

100

50

0

0

0.5

1

1.5

2

2.5

3

3.5

-50

-100

-150

-200

VCXO input [V]

Document #: 38-07734 Rev. *B

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