Datasheet

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General Description

The DS1090 is a low-cost, dithered oscillator intended

to be used as an external clock for switched-mode

power supplies and other low-frequency applications.

The dithering or sweeping function reduces peak-radi-

ated emissions from the power supply at its fundamen-

tal frequency, as well as harmonic frequencies. The

device consists of a resistor-programmed master oscil-

lator, factory-programmed clock prescaler, and a pin-

programmed dither circuit. These features allow the

DS1090 to be used in applications where a spread-

spectrum clock is desired to reduce radiated emis-

sions. A combination of factory-set prescalers and

external resistor allows for output frequencies ranging

from 125kHz to 8MHz. Both dither frequency and dither

percentage are set using control pins.

Applications

Switched-Mode Power Supplies

Servers

Printers

Embedded Microcontrollers

Industrial Controls

Automotive Applications

Features

♦ Low-Cost, Spread-Spectrum EconOscillator™

♦ Simple User Programming

♦ Output Frequency Programmable from 125kHz

to 8MHz

♦ Dither Percentage Programmable from 0% to 8%

♦ Dither Rate Programmable (f

MOSC

/ 512, 1024,

2048, or 4096 )

♦ 3.0V to 5.5V Single-Supply Operation

♦ CMOS/TTL-Compatible Output

♦ Operating Temperature Range: -40°C to +85°C

DS1090

Low-Frequency, Spread-Spectrum

EconOscillator

______________________________________________

Maxim Integrated Products

J0GND

JC1

JC0R

SET

OUT

μSOP

TOP VIEW

DS1090

Pin Configuration

Ordering Information

DS1090

OUT

DC-DC

STEP-DOWN

CONVERTER

OUT

GND

SET

JC0

JC1

45kΩ

TO 91kΩ

Typical Operating Circuit

Rev 1; 2/07

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Add “T” for Tape & Reel orders.

PART

OUTPUT

FREQUENCY

RANGE

PRESCALER

PIN-

PACKAGE

DS1090U-1+ 4MHz to 8MHz 1 8 μSOP

DS1090U-2+ 2MHz to 4MHz 2 8 μSOP

DS1090U-4+ 1MHz to 2MHz 4 8 μSOP

DS1090U-8+

500kHz to

1MHz

8 8 μSOP

DS1090U-16+

250kHz to

500kHz

16 8 μSOP

DS1090U-32+

125kHz to

250kHz

32 8 μSOP

EconOscillator is a trademark of Dallas Semiconductor.

Summary of content (8 pages)

PAGE 1
Rev 1; 2/07 Low-Frequency, Spread-Spectrum EconOscillator The DS1090 is a low-cost, dithered oscillator intended to be used as an external clock for switched-mode power supplies and other low-frequency applications. The dithering or sweeping function reduces peak-radiated emissions from the power supply at its fundamental frequency, as well as harmonic frequencies. The device consists of a resistor-programmed master oscillator, factory-programmed clock prescaler, and a pinprogrammed dither circuit.
PAGE 2
DS1090 Low-Frequency, Spread-Spectrum EconOscillator ABSOLUTE MAXIMUM RATINGS Voltage Range on VCC Relative to Ground ...........-0.5V to +6.0V Voltage Range on Input Pins Relative to Ground.................................-0.5V to (VCC + 0.5V), not to exceed 6.0V Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-55°C to +125°C Soldering Temperature .......................................
PAGE 3
Low-Frequency, Spread-Spectrum EconOscillator DS1090 AC ELECTRICAL CHARACTERISTICS (VCC = +3.0V to +5.5V, TA = -40°C to +85°C, unless otherwise noted.) PARAMETER SYMBOL Internal Master Oscillator Frequency fMOSC Output Frequency Tolerance f OUT Voltage Frequency Variation Temperature Frequency Variation f OUT f OUT Peak-to-Peak Dither (3 ) (Note 5) Power-Up Time Load Capacitance Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: MAX UNITS 4.0 8.0 MHz VCC = 3.3V, TA = +25°C -3.
PAGE 4
Typical Operating Characteristics (VCC = +3.3V, TA = +25°C, unless otherwise noted.) 40kΩ 60kΩ 0.95 40kΩ 1.10 60kΩ 0.90 DS1090 toc03 TA = +25°C, RSET = 40kΩ SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) 1.45 NO LOAD, VCC = 3.3V 1.30 4 DS1090 toc02 NO LOAD, TA = +25°C SUPPLY CURRENT (mA) 1.50 DS1090 toc01 1.70 1.20 SUPPLY CURRENT vs. OUTPUT LOADING SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT vs. SUPPLY VOLTAGE 0.70 5V 3 4V 2 3V 1 80kΩ 80kΩ 0 3.5 4.0 4.5 5.0 -40 5.
PAGE 5
Low-Frequency, Spread-Spectrum EconOscillator RESISTOR CURRENT vs. RESISTOR VALUE DUTY CYCLE vs. TEMPERATURE 9 RSET = 40kΩ 8 7 DUTY CYCLE (%) FREQUENCY (MHz) 51 40kΩ 60kΩ 80kΩ 6 VCC = 3.3V 50 VCC = 5V 49 18 VCC = 3.3V, TA = +25°C RESISTOR CURRENT (μA) VCC = 3.3V DS1090 toc08 52 DS1090 toc07 10 DS1090 toc09 OUTPUT FREQUENCY vs. TEMPERATURE 16 14 12 10 5 DS1090U-1 -15 10 35 60 85 -15 10 35 FREQUENCY ERROR vs. SUPPLY VOLTAGE (FROM 3.3V) FREQUENCY ERROR vs.
PAGE 6
Low-Frequency, Spread-Spectrum EconOscillator DS1090 Pin Description PIN NAME FUNCTION 1 OUT Oscillator Output 2 RSET Frequency Control Resistor Input 3 VCC Positive-Supply Terminal 4 GND Ground 5 J0 6 J1 7 JC0 8 JC1 Dither Amplitude (Percentage) Inputs (see Table 2) Dither Rate Divisor Inputs (see Table 1) Block Diagram RSET DS1090 VOLTAGEBIAS CIRCUIT MASTER OSCILLATOR (VCO) + ∑ fMOSC + FACTORY PROGRAMMED PRESCALER (÷ 1, 2, 4, 8, 16, OR 32) 4MHz–8MHz VCC VCC DITHER GENERAT
PAGE 7
Low-Frequency, Spread-Spectrum EconOscillator (+ 1, 2, or 4% of fMOSC) Programmed fMOSC DITHER AMOUNT (2, 4, OR 8%) (- 1, 2, or 4% of fMOSC) 1 fMOD fMOSC 8 fMOSC (MHz) IF DITHER AMOUNT = 0% DS1090 fig01 9 DS1090 MASTER OSCILLATOR FREQUENCY vs. EXTERNAL RESISTOR SELECTION 7 6 TIME 5 Figure 2. Center Frequency Dither Diagram 4 Factory-Programmed Prescaler 3 40 50 60 80 70 90 RSET RESISTANCE (kΩ) Figure 1.
PAGE 8
DS1090 Low-Frequency, Spread-Spectrum EconOscillator Table 2. Dither Percentage Setting J1 J0 DITHER PERCENT (%) 0 0 0 0 1 2 1 0 4 1 1 8 RSET Resistor Selection The value of the resistor used to select the desired frequency is calculated using the formula in the Master Oscillator section (see also Figure 1). It is recommended to use, at minimum, a 1%-tolerance, 1/16th-watt component with a temperature coefficient that satisfies the overall stability requirements desired of the end-equipment.