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Rev 0; 4/04
Low-Frequency, Spread-Spectrum EconOscillator
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-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. These features allow the DS1090 to be used in applications where a spreadspectrum clock is desired to reduce radiated emissions. 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.
Features
Low-Cost, Spread-Spectrum EconOscillatorTM Simple User Programming Output Frequency Programmable from 125kHz to 8MHz Dither Percentage Programmable from 0% to 8% Dither Rate Programmable (fMOSC / 512, 1024, 2048, or 4096 ) 3.0V to 5.5V Single-Supply Operation CMOS/TTL-Compatible Output Operating Temperature Range: -40C to +85C
DS1090
Ordering Information
PART OUTPUT FREQUENCY RANGE 4MHz to 8MHz 2MHz to 4MHz 1MHz to 2MHz 500kHz to 1MHz 250kHz to 500kHz 125kHz to 250kHz PRESCALER 1 2 4 8 16 32 PINPACKAGE 8 SOP 8 SOP 8 SOP 8 SOP 8 SOP 8 SOP
Applications
Switched-Mode Power Supplies Servers Printers Embedded Microcontrollers Industrial Controls Automotive Applications
DS1090U-1 DS1090U-2* DS1090U-4* DS1090U-8* DS1090U-16 DS1090U-32*
Add "/T" for Tape & Reel orders. *Contact factory for availability.
Typical Operating Circuit
VIN VOUT
Pin Configuration
TOP VIEW
VCC DC-DC STEP-DOWN CONVERTER OUT JC0
OUT 1 RSET 2
8 7
JC1 JC0 J1 J0
VCC
DS1090
VCC 3 6 5 GND 4
DS1090 JC1
RSET 45k TO 91k GND J0 J1
SOP
EconOscillator is a trademark of Dallas Semiconductor. ______________________________________________ Maxim Integrated Products 1
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.
Low-Frequency, Spread-Spectrum EconOscillator DS1090
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 ...........................-40C to +85C Storage Temperature Range .............................-55C to +125C Soldering Temperature .......................................See IPC/JEDEC J-STD-020A Specification
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED DC OPERATING CONDITIONS
(TA = -40C to +85C)
PARAMETER Supply Voltage Input Logic 1 (J0, J1, JC0, JC1) Input Logic 0 (J0, J1, JC0, JC1) SYMBOL VCC VIH VIL (Note 1) CONDITIONS MIN 3.0 0.7 x VCC -0.3 TYP MAX 5.5 VCC + 0.3 +0.3 x VCC UNITS V V V
DC ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +5.5V, TA = -40C to +85C, unless otherwise noted.)
PARAMETER Supply Current High-Level Output Voltage (OUT) Low-Level Output Voltage (OUT) High-Level Input Current (J0, J1, JC0, JC1) Low-Level Input Current (J0, J1, JC0, JC1) Resistor Current SYMBOL ICC VOH VOL IIH IIL IRES CONDITIONS CL = 15pF, VCC = 3.3V, RSET = 40k CL = 15pF, VCC = 5.5V, RSET = 40k IOH = -4mA VCC = min IOL = 4mA VIH = VCC VIL = 0V VCC = max -1.0 150 2.4 0.4 +1.0 MIN TYP 1.4 1.7 3 MAX UNITS mA V V A A A
2
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Low-Frequency, Spread-Spectrum EconOscillator DS1090
AC ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +5.5V, TA = -40C to +85C, unless otherwise noted.)
PARAMETER Internal Master Oscillator Frequency Output Frequency Tolerance SYMBOL fMOSC fOUT VCC = 3.3V, TA = +25C TA = +25C, RSET = 60k, VCC = 3.0V to 3.6V (Notes 2, 3) TA = +25C, RSET = 60k, VCC = 4.5V to 5.5V (Notes 2, 3) VCC = 3.3V (Notes 2, 3, 4) J0 = GND, J1 = GND Peak-to-Peak Dither (3) (Note 5) J0 = VCC, J1 = GND J0 = GND, J1 = VCC J0 = VCC, J1 = VCC Power-Up Time Load Capacitance Output Duty Cycle Output Rise/Fall Time tR, tF tPOR + tSTAB CL (Note 6) (Note 7) 4MHz to 8MHz, TA = +25C (Note 3) <4MHz (Note 4) CL = 15pF 45 50 20 CONDITIONS MIN 4.0 -11.5 -0.3 -1.25 -2.5 0 2 4 8 0.1 0.5 30 55 ms pF % ns % TYP MAX 8.0 +11.5 +0.3 % +1.25 +2.5 % UNITS MHz %
Voltage Frequency Variation
fOUT
Temperature Frequency Variation
fOUT
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6:
Note 7:
All voltages referenced to ground. This is the change observed in output frequency due to changes in temperature or voltage. See the Typical Operating Characteristics section. Parameter is guaranteed by design and is not production tested. This is a percentage of the output period. Parameter is characterized but not production tested. This can be varied from 0% to 8%. This indicates the time between power-up and the outputs becoming active. An on-chip delay is intentionally introduced to allow the oscillator to stabilize. tSTAB is equivalent to ~500 clock cycles and is dependent upon the programmed output frequency. Output voltage swings can be impaired at high frequencies combined with high output loading.
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3
Low-Frequency, Spread-Spectrum EconOscillator DS1090
Typical Operating Characteristics
(VCC = +3.3V, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
DS1090 toc01
SUPPLY CURRENT vs. TEMPERATURE
DS1090 toc02
SUPPLY CURRENT vs. OUTPUT LOADING
TA = +25C, RSET = 40k SUPPLY CURRENT (mA) 3 5V 4V 2 3V
DS1090 toc03
1.70 NO LOAD, TA = +25C SUPPLY CURRENT (mA) 1.45 40k 1.20 60k
1.50 NO LOAD, VCC = 3.3V 1.30 SUPPLY CURRENT (mA) 40k
4
1.10 60k 0.90
0.95 80k 0.70 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
0.70 80k 0.50 -40 -15 10 35 60 85 TEMPERATURE (C)
1
0 5 10 15 20 25 30 35 40 LOAD CAPACITANCE (pF)
OUTPUT VOLTAGE HIGH vs. OUTPUT CURRENT
DS1090 toc04
OUTPUT VOLTAGE LOW vs. OUTPUT CURRENT
DS1090 toc05
OUTPUT FREQUENCY vs. SUPPLY VOLTAGE
TA = +25C 9 FREQUENCY (MHz) 8 7 6 5 40k
DS1090 toc06
3.1 VCC = 3.0V OUTPUT VOLTAGE (V) 3.0
0.4 VCC = 3.0V OUTPUT VOLTAGE (V) 0.3
10
2.9
0.2
60k 80k
2.8
0.1
2.7 -5 -4 -3 -2 -1 0 OUTPUT CURRENT (mA)
0 0 1 2 3 4 5 OUTPUT CURRENT (mA)
4 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
4
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Low-Frequency, Spread-Spectrum EconOscillator DS1090
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = +25C, unless otherwise noted.)
OUTPUT FREQUENCY vs. TEMPERATURE
DS1090 toc07
DUTY CYCLE vs. TEMPERATURE
DS1090 toc08
RESISTOR CURRENT vs. RESISTOR VALUE
VCC = 3.3V, TA = +25C RESISTOR CURRENT (A) 16
DS1090 toc09
10 VCC = 3.3V 9 FREQUENCY (MHz) 8 7 80k 6 5 60k 40k
52 RSET = 40k 51 DUTY CYCLE (%) VCC = 3.3V 50
18
14
12
49
VCC = 5V
10 DS1090U-1
4 -40 -15 10 35 60 85 TEMPERATURE (C)
48 -40 -15 10 35 60 85 TEMPERATURE (C)
8 40 50 60 RSET (k) 70 80
FREQUENCY ERROR vs. SUPPLY VOLTAGE (FROM 3.3V)
DS1090 toc10
FREQUENCY ERROR vs. TEMPERATURE (FROM +25C)
DS1090 toc11
POWER SPECTRUM vs. SPREAD
-10 -20 POWER (dBm) -30 -40 -50 -60 OFF VCC = 3.3V, TA = +25C, JC0 = JC1 = 1
DS1090 toc12
5.0 TA = +25C FREQUENCY ERROR (%) 2.5 80k 0
2.0 VCC = 3.3V FREQUENCY ERROR (%) 1.0 60k
0
2% 4% 8%
0 80k -1.0 40k -2.0
-2.5
40k 60k
-70 -80 4.80 5.35 FREQUENCY (MHz) 5.90
-5.0 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
-40
-15
10
35
60
85
TEMPERATURE (C)
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5
Low-Frequency, Spread-Spectrum EconOscillator DS1090
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME OUT RSET VCC GND J0 J1 JC0 JC1 FUNCTION Oscillator Output Frequency Control Resistor Input Positive-Supply Terminal Ground Dither Amplitude (Percentage) Inputs (see Table 2) Dither Rate Divisor Inputs (see Table 1)
Block Diagram
RSET
VOLTAGEBIAS CIRCUIT MASTER OSCILLATOR (VCO)
DS1090
+
+
fMOSC
FACTORY PROGRAMMED PRESCALER (/ 1, 2, 4, 8, 16, OR 32)
fOSC BUFFER
fOUT OUT
4MHz-8MHz VCC VCC DITHER GENERATOR GND + DITHER AMPLITUDE (0, 2, 4, OR 8%) f MOD TRIANGLE GENERATOR (/ 128) DITHER RATE (/ 4, 8, 16, OR 32)
J0 J1 JC0 JC1
6
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Low-Frequency, Spread-Spectrum EconOscillator DS1090
MASTER OSCILLATOR FREQUENCY vs. EXTERNAL RESISTOR SELECTION
DS1090 fig01
IF DITHER AMOUNT = 0% (+ 1, 2, or 4% of fMOSC) Programmed fMOSC (- 1, 2, or 4% of fMOSC) 1 fMOD DITHER AMOUNT (2, 4, OR 8%)
9 8 7 6
fMOSC (MHz)
fMOSC
TIME 5
Figure 2. Center Frequency Dither Diagram
4 3 40 50 60 70 80 90 RSET RESISTANCE (k)
Factory-Programmed Prescaler
The prescaler divides the frequency of the master oscillator by 1, 2, 4, 8, 16, or 32 to generate the squarewave output clock (fOSC). This divisor is factory-set and is an ordering option.
Figure 1. Master Oscillator Frequency
Detailed Description
The DS1090 is a center-dithered, spread-spectrum silicon oscillator for use as an external clock in reducedEMI applications. With a combination of factoryprogrammed prescalers and a user-selected external resistor, output frequencies from 125kHz to 8MHz can be achieved. The output center frequency can be dithered by selecting the desired dither rate and amplitude with discrete inputs J0, J1, JC0, and JC1. The DS1090 contains four basic circuit blocks: master oscillator, factory-programmed prescaler, dither generator, and the voltage-bias circuit that provides the feedback path to the master oscillator for frequency control and dithering functions.
Dither Generator
Spread-spectrum functionality is achieved by a userconfigurable divider (determines dither rate), a triangle generator, and a user-configurable dither amplitude circuit (see Block Diagram). The input to the triangle-wave generator is derived from the internal master oscillator and is fed through a userconfigurable divider. The settings of control pins JC0 and JC1 determine this dither rate divisor setting (see Table 1), dividing the master clock by 4, 8, 16, or 32. The clock signal is further divided by 128 in the triangle-wave generator, which results in a trianglewave signal of either 1/512th, 1/1024th, 1/2048th, or 1/4096th of the master oscillator (f MOD), depending upon the user's divisor setting. The dithering frequency can be also expressed as the result of fMOD = fMOSC Divisor x128
Master Oscillator
The master oscillator is programmable in the application by the use of an external resistor (RSET) tied to ground (GND). Resistor values of 45k to 91k vary the square-wave output frequency of the voltage-controlled master oscillator (fMOSC) from 8MHz down to 4MHz (see Figure 1). The master oscillator (Hz) frequency can be stated as fMOSC 3.6461E +11 Re sistor
where Divisor is 4, 8, 16, or 32.
Table 1. Dither Rate Divisor Settings
JC1 0 0 1 1 JC0 0 1 0 1 DITHERING PERCENTAGE (fMOSC/n) FMOSC / 512 FMOSC / 1024 fMOSC / 2048 fMOSC / 4096 DIVISOR SETTING 4 8 16 32
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7
Low-Frequency, Spread-Spectrum EconOscillator DS1090
Table 2. Dither Percentage Setting
J1 0 0 1 1 J0 0 1 0 1 DITHER PERCENT (%) 0 2 4 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. Place the external RSET resistor as close as possible to minimize lead inductance.
Dither Percentage Settings
Dither amplitude (measured in percent from the master oscillator center frequency) is set using input pins J0 and J1. This circuit uses a sense current from the master oscillator bias circuit to adjust the amplitude of the triangle-wave signal to a voltage level that modulates the master oscillator to a percentage of its resistor-set center frequency. This percentage is set in the end application to be 0%, 2%, 4%, or 8% (see Table 2).
Power-Supply Decoupling
To achieve best results, it is highly recommended that a decoupling capacitor is used on the IC power-supply pins. Typical values of decoupling capacitors are 0.01F and 0.1F. Use a high-quality, ceramic, surface-mount capacitor, and mount it as close as possible to the VCC and GND pins of the IC to minimize lead inductance.
Application Information
Pin Connection
The DS1090 is intended to provide a fixed-frequency, dithered clock to be used as a clock driver for DC-DC converters and other applications requiring a lowfrequency EMI-reduced clock oscillator. All control pins must be biased per Tables 1 and 2 for proper operation for the individual application's requirements. RSET must be tied to ground (GND) by a customer-supplied resistor.
Chip Information
TRANSISTOR COUNT: 1883 SUBSTRATE CONNECTED TO GROUND
Package Information
For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
is a registered trademark of Dallas Semiconductor Corporation.

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