Low-Frequency, Spread-Spectrum EconOscillator

Transcription

1 General Description The DS19 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 pin-programmed dither circuit. These features allow the DS19 to be used in applications where a spread-spectrum clock is desired to reduce radiated emissions. A combination of factory-set prescalers and external resistor allows for output frequencies ranging from 125kHz to MHz. Both dither frequency and dither percentage are set using control pins. Applications Switched-Mode Power Supplies Servers Printers Embedded Microcontrollers Industrial Controls Typical Operating Circuit V IN V Features Low-Cost, Spread-Spectrum EconOscillator Simple User Programming Output Frequency Programmable from 125kHz to MHz Dither Percentage Programmable from % to % Dither Rate Programmable (f MOSC /512, 12, 2, or 96) 3.V to 5.5V Single-Supply Operation CMOS/TTL-Compatible Output Operating Temperature Range: - C to +5 C Ordering Information PART PUT FREQUENCY RANGE Add T for Tape & Reel orders. PRESCALER PIN- PACKAGE DS19U-1+ MHz to MHz 1 µsop DS19U-2+ 2MHz to MHz 2 µsop DS19U-+ 1MHz to 2MHz µsop DS19U-+ DS19U-16+ DS19U-32+ 5kHz to 1MHz 25kHz to 5kHz 125kHz to 25kHz Pin Configuration µsop 16 µsop 32 µsop DC-DC STEP-DOWN CONVERTER TOP VIEW 5kΩ TO 91kΩ R SET DS19 GND JC JC1 J J1 R SET GND DS JC1 JC J1 J µsop EconOscillator is a trademark of Maxim Integrated Products, Inc ; Rev 3; 9/16

2 Absolute Maximum Ratings Voltage Range on Relative to Ground...-.5V to +6.V Voltage Range on Input Pins Relative to Ground V to ( +.5V), not to exceed 6.V Operating Temperature Range... - C to +5 C Storage Temperature Range C to +125 C Soldering Temperature...See IPC/JEDEC J-STD-2A 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 (T A = - C to +5 C) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Supply Voltage (Note 1) V.7 x V Input Logic 1 (J, J1, JC, JC1) + IH V.3 Input Logic (J, J1, JC, JC1) V IL x V DC Electrical Characteristics ( = +3.V to +5.5V, T A = - C to +5 C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS C L = 15pF, = 3.3V, R SET = 1. Supply Current I CC ma CL = 15pF, = 5.5V, R SET = I OH = -ma High-Level Output Voltage () V OH 2. V = min Low-Level Output Voltage () VOL I OL = ma. V High-Level Input Current (J, J1, JC, JC1) Low-Level Input Current (J, J1, JC, JC1) I IH V IH = VCC +1. µa I IL V IL = V -1. µa Resistor Current I RES = max 15 µa Maxim Integrated 2

3 AC Electrical Characteristics ( = +3.V to +5.5V, T A = - C to +5 C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Internal Master Oscillator Frequency f MOSC.. MHz V Output Frequency Tolerance f CC = 3.3V, T A = +25 C % Voltage Frequency Variation f T A = +25 C, R SET =, = 3.V to 3.6V (Notes 2, 3) T A = +25 C, R SET =, =.5V to 5.5V (Notes 2, 3) % V Temperature Frequency Variation f CC = 3.3V (Notes 2, 3, ) % J = GND, J1 = GND Peak-to-Peak Dither (3σ) J = VCC, J1 = GND 2 (Note 5) J = GND, J1 = % J =, J1 = Power-Up Time t POR + t STAB (Note 6).1.5 ms Load Capacitance C L (Note 7) 3 pf Output Duty Cycle MHz to MHz, T A = +25 C (Note 3) 5 55 <MHz (Note ) 5 % Output Rise/Fall Time t R, t F C L = 15pF 2 ns Note 1: All voltages referenced to ground. Note 2: This is the change observed in output frequency due to changes in temperature or voltage. Note 3: See the Typical Operating Characteristics section. Note : Parameter is guaranteed by design and is not production tested. Note 5: This is a percentage of the output period. Parameter is characterized but not production tested. This can be varied from % to %. Note 6: 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. t STAB is equivalent to ~5 clock cycles and is dependent upon the programmed output frequency. Note 7: Output voltage swings can be impaired at high frequencies combined with high output loading. Maxim Integrated 3

4 Typical Operating Characteristics ( = +3.3V, T A = +25 C, unless otherwise noted.) SUPPLY CURRENT (ma) NO LOAD, T A = +25 C SUPPLY CURRENT vs. SUPPLY VOLTAGE SUPPLY VOLTAGE (V) DS19 toc1 SUPPLY CURRENT (ma) SUPPLY CURRENT vs. TEMPERATURE NO LOAD, = 3.3V TEMPERATURE ( C) DS19 toc2 SUPPLY CURRENT (ma) SUPPLY CURRENT vs. PUT LOADING T A = +25 C, R SET = LOAD CAPACITANCE (pf) 5V V 3V DS19 toc3 PUT VOLTAGE (V) = 3.V PUT VOLTAGE HIGH vs. PUT CURRENT DS19 toc PUT VOLTAGE (V) = 3.V PUT VOLTAGE LOW vs. PUT CURRENT DS19 toc5 FREQUENCY (MHz) PUT FREQUENCY vs. SUPPLY VOLTAGE T A = +25 C DS19 toc PUT CURRENT (ma) PUT CURRENT (ma) SUPPLY VOLTAGE (V) Maxim Integrated

5 Typical Operating Characteristics (continued) ( = +3.3V, T A = +25 C, unless otherwise noted.) FREQUENCY (MHz) = 3.3V PUT FREQUENCY vs. TEMPERATURE TEMPERATURE ( C) DS19 toc7 DUTY CYCLE (%) DS19U-1 DUTY CYCLE vs. TEMPERATURE = 5V = 3.3V TEMPERATURE ( C) R SET = DS19 toc RESISTOR CURRENT (ma) RESISTOR CURRENT vs. RESISTOR VALUE = 3.3V, T A = +25 C R SET (kω) DS19 toc9 FREQUENCY ERROR (%) FREQUENCY ERROR vs. SUPPLY VOLTAGE (FROM 3.3V) T A = +25 C DS19 toc1 FREQUENCY ERROR (%) FREQUENCY ERROR vs. TEMPERATURE (FROM +25 C) = 3.3V DS19 toc11 POWER (dbm) % % % POWER SPECTRUM vs. SPREAD OFF = 3.3V, T A = +25 C, JC = JC1 = 1 DS19 toc SUPPLY VOLTAGE (V) TEMPERATURE ( C) FREQUENCY (MHz) Maxim Integrated 5

6 Pin Description PIN NAME FUNCTION 1 Oscillator Output 2 R SET Frequency Control Resistor Input 3 Positive-Supply Terminal GND Ground 5 J Dither Amplitude (Percentage) Inputs 6 J1 (see Table 2) 7 JC Dither Rate Divisor Inputs (see Table 1) JC1 Block Diagram R SET VOLTAGE- BIAS CIRCUIT DS MASTER OSCILLATOR (VCO) MHz MHz f MOSC FACTORY PROGRAMMED PRESCALER ( 1, 2,,, 16, OR 32) f OSC BUFFER f DITHER GENERATOR GND + - DITHER AMPLITUDE TRIANGLE GENERATOR DITHER RATE (, 2,, OR %) f MOD ( 12) (,, 16, OR 32) J J1 JC JC1 Maxim Integrated 6

7 fmosc (MHz) MASTER OSCILLATOR FREQUENCY vs. EXTERNAL RESISTOR SELECTION Figure 1. Master Oscillator Frequency 5 6 Detailed Description The DS19 is a center-dithered, spread-spectrum silicon oscillator for use as an external clock in reduced-emi applications. With a combination of factory-programmed prescalers and a user-selected external resistor, output frequencies from 125kHz to MHz can be achieved. The output center frequency can be dithered by selecting the desired dither rate and amplitude with discrete inputs J, J1, JC, and JC1. The DS19 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. Master Oscillator The master oscillator is programmable in the application by the use of an external resistor (R SET ) tied to ground (GND). Resistor values of 5kΩ to 91kΩ vary the square-wave output frequency of the voltage-controlled master oscillator (f MOSC ) from MHz down to MHz (see Figure 1). The master oscillator (Hz) frequency can be stated as 7 R SET RESISTANCE (kω) E+ 11 fmosc Resistor 9 DS19 fig1 Figure 2. Center Frequency Dither Diagram Factory-Programmed Prescaler The prescaler divides the frequency of the master oscillator by 1, 2,,, 16, or 32 to generate the square-wave output clock (f OSC ). This divisor is factory-set and is an ordering option. 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 user-configurable divider. The settings of control pins JC and JC1 determine this dither rate divisor setting (see Table 1), dividing the master clock by,, 16, or 32. The clock signal is further divided by 12 in the triangle-wave generator, which results in a triangle-wave signal of either 1/512th, 1/12th, 1/2th, or 1/96th of the master oscillator (f MOD ), depending upon the user s divisor setting. The dithering frequency can be also expressed as the result of f f MOSC MOD= Divisor 12 where Divisor is,, 16, or 32. Table 1. Dither Rate Divisor Settings JC1 (+ 1, 2, or % of f MOSC ) Programmed f MOSC (- 1, 2, or % of f MOSC ) JC fmosc 1 f MOD TIME IF DITHER AMOUNT = % DITHERING PERCENTAGE (f MOSC /n) DITHER AMOUNT (2,, OR %) DIVISOR SETTING f MOSC /512 1 f MOSC /12 1 f MOSC / f MOSC / Maxim Integrated 7

8 Table 2. Dither Percentage Setting J1 J DITHER PERCENT (%) Dither Percentage Settings Dither amplitude (measured in percent ± from the master oscillator center frequency) is set using input pins J 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 %, 2%, %, or % (see Table 2). Application Information Pin Connection The DS19 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. R SET must be tied to ground (GND) by a customer-supplied resistor. R SET 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 R SET resistor as close as possible to minimize lead inductance. 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.1µf and.1µf. Use a high-quality, ceramic, surface-mount capacitor, and mount it as close as possible to the and GND pins of the IC to minimize lead inductance. Chip Information SUBSTRATE CONNECTED TO GROUND Package Information For the latest package outline information and land patterns (footprints), go to Note that a +, #, or - in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. Maxim Integrated

9 Revision History REVISION NUMBER REVISION DATE DESCRIPTION PAGES CHANGED 1 2/7 2 2/15 Remove automotive reference from data sheet 1 3 9/16 Corrected typo in Benefits and Features section 1 For pricing, delivery, and ordering information, please contact Maxim Direct at , or visit Maxim Integrated s website at Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. 216 Maxim Integrated Products, Inc. 9