ON NB2779A Schematic [ru]

NB2779A

Low Power, Reduced EMI Clock Synthesizer

The NB2779A is a versatile spread spectrum frequency modulator designed specifically for a wide range of clock frequencies. The NB2779A reduces ElectroMagnetic Interference (EMI) at the clock source, allowing system wide reduction of EMI of all clock dependent signals. The NB2779A allows significant system cost savings by reducing the number of circuit board layers, ferrite beads and shielding that are traditionally required to pass EMI regulations.

The NB2779A uses the most efficient and optimized modulation profile approved by the FCC and is implemented by using a proprietary all digital method.

The NB2779A modulates the output of a single PLL in order to “spread” the bandwidth of a synthesized clock, and more importantly, decreases the peak amplitudes of its harmonics. This results in significantly lower system EMI compared to the typical narrow band signal produced by oscillators and most frequency generators. Lowering EMI by increasing a signal’s bandwidth is called ‘spread spectrum clock generation’.

The NB2779A is targeted towards all portable devices with very low power requirements like MP3 players and digital still cameras.

Features

• Generates an EMI Optimized Clocking Signal at the Output

• Integrated Loop Filter Components

• Operates with a 3.3 V / 2.5 V Supply

• Operating Current less than 4.0 mA

• Low Power CMOS Design

• Input Frequency Range: 13 MHz to 30 MHz for Both Voltages

• Generates a 1X Low EMI Spread Spectrum clock of the Input

Frequency

• Frequency Deviation "1% @ 16 MHz

• Available in TSOP−6 Package (TSOT−23−6)

• Pb−Free Package is Available

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MARKING

DIAGRAM*

(Note: Microdot may be in either location)

*For additional marking information, refer to

Application Note AND8002/D.

ORDERING INFORMATION

See detailed ordering and shipping information in the package dimensions section on page 7 of this data sheet.

TSOP−6

(TSOT−23−6)

SN SUFFIX

CASE 318G

E06 = Specific Device Code A = Assembly Location Y = Year W = Work Week G = Pb−Free Package

E06AYWG

December, 2006 − Rev. 3

1 Publication Order Number:

NB2779A/D

NB2779A

Modulation

XIN/CLKIN

XOUT

Crystal

Oscillator

Frequency

Divider

Feedback

Divider

Phase

Detector

Loop Filter

Figure 1. Block Diagram

Table 1. KEY SPECIFICATIONS

Description Specification

Supply Voltages VDD = 3.3 V / 2.5 V

Frequency Range For 2.5 V Supply

For 3.3 V Supply

Cycle−to−Cycle Jitter 200 ps (maximum)

Output Duty Cycle 45/55% (worst case)

Modulation Rate Equation FIN/640

Frequency Deviation "1% (TYP) @ 16 MHz

13 MHz < CLKIN < 30 MHz 13 MHz < CLKIN < 30 MHz

PLL

Output Divider

ModOUT

XOUT

XIN/CLKIN

NB2779A

ModOUT

Figure 2. Pin Configuration

Table 2. PIN DESCRIPTION

Pin # Pin Name Type Description

1 PD I Powerdown control pin. Pull low to enable powerdown mode. Connect to VDD if not used.

2 XOUT O Crystal connection. If using an external reference, this pin must be left unconnected.

3 XIN/CLKIN I Crystal connection or external reference frequency input. This pin has dual functions. It can be

4 V

5 ModOUT O Spread spectrum clock output.

6 V

connected either to an external crystal or an external reference clock.

P Power supply for the entire chip.

P Ground connection.

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NB2779A

Figure 3. Modulation Profile

Table 3. MAXIMUM RATINGS

Symbol Description Rating Unit

DD,

STG

Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability.

Voltage on any pin with respect to Ground 0.5 to +7.0 V

Storage Temperature −65 to +125 °C

Operating Temperature 0 to 70 °C

Max. Soldering Temperature (10 sec) 260 °C

Junction Temperature 150 °C

Static Discharge Voltage (As per MIL−STD−883, Method 3015) 2 kV

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