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: -40c to +85c ds1090 low-frequency, spread-spectrum econoscillator ______________________________________________ maxim integrated products 1 j1 j0 gnd 1 2 8 7 jc1 jc0 r set v cc out sop top view 3 4 6 5 ds1090 pin configuration ordering information ds1090 v out v in dc-dc step-down converter out gnd v cc v cc r set jc0 jc1 j0 j1 45k to 91k 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? website at www.maxim-ic.com. add ??for tape & reel orders. part output frequency range prescaler pin- package ds1090u-1+ 4mhz to 8mhz 1 8 sop ds1090u-2+ 2mhz to 4mhz 2 8 sop ds1090u-4+ 1mhz to 2mhz 4 8 sop ds1090u-8+ 500khz to 1mhz 8 8 sop ds1090u-16+ 250khz to 500khz 16 8 sop ds1090u-32+ 125khz to 250khz 32 8 sop econoscillator is a trademark of dallas semiconductor.
ds1090 low-frequency, spread-spectrum econoscillator 2 _____________________________________________________________________ absolute maximum ratings recommended dc operating conditions (t a = -40? to +85?) dc electrical characteristics (v cc = +3.0v to +5.5v, t a = -40? to +85?, unless otherwise noted.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. voltage range on v cc relative to ground ...........-0.5v to +6.0v voltage range on input pins relative to ground.................................-0.5v to (v cc + 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 .......................................see ipc/jedec j-std-020a specification parameter symbol conditions min typ max units supply voltage v cc (note 1) 3.0 5.5 v input logic 1 (j0, j1, jc0, jc1) v ih 0.7 x v cc v cc + 0.3 v input logic 0 (j0, j1, jc0, jc1) v il -0.3 +0.3 x v cc v parameter symbol conditions min typ max units c l = 15pf, v cc = 3.3v, r set = 40k 1.4 supply current i cc c l = 15pf, v cc = 5.5v, r set = 40k 1.7 3 ma i oh = -4ma high-level output voltage (out) v oh v cc = min 2.4 v low-level output voltage (out) v ol i ol = 4ma 0.4 v high-level input current (j0, j1, jc0, jc1) i ih v ih = v cc +1.0 ? low-level input current (j0, j1, jc0, jc1) i il v il = 0v -1.0 ? resistor current i res v cc = max 150 ?
ds1090 low-frequency, spread-spectrum econoscillator _____________________________________________________________________ 3 parameter symbol conditions min typ max units internal master oscillator frequency f mosc 4.0 8.0 mhz output frequency tolerance f out v cc = 3.3v, t a = +25c -3.0 +3.0 % t a = +25c, r set = 60k , v cc = 3.0v to 3.6v (notes 2, 3) -0.5 +0.5 voltage frequency variation f out t a = +25c, r set = 60k , v cc = 4.5v to 5.5v (notes 2, 3) -1.25 +1.25 % temperature frequency variation f out v cc = 3.3v (notes 2, 3, 4) -2.0 +2.0 % j0 = gnd, j1 = gnd 0 j0 = v cc , j1 = gnd 2 j0 = gnd, j1 = v cc 4 peak-to-peak dither (3 ) (note 5) j0 = v cc , j1 = v cc 8 % power-up time t por + t stab (note 6) 0.1 0.5 ms load capacitance c l (note 7) 30 pf 4mhz to 8mhz, t a = +25c (note 3) 45 55 output duty cycle <4mhz (note 4) 50 % output rise/fall time t r , t f c l = 15pf 20 ns ac electrical characteristics (v cc = +3.0v to +5.5v, t a = -40? to +85?, unless otherwise noted.) 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 4: 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 0% to 8%. 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 ~500 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.
ds1090 low-frequency, spread-spectrum econoscillator 4 _____________________________________________________________________ typical operating characteristics (v cc = +3.3v, t a = +25?, unless otherwise noted.) supply current vs. supply voltage ds1090 toc01 supply voltage (v) supply current (ma) 5.0 4.5 4.0 3.5 0.95 1.20 1.45 1.70 0.70 3.0 5.5 no load, t a = +25 c 40k 60k 80k supply current vs. temperature ds1090 toc02 temperature ( c) supply current (ma) 60 35 10 -15 0.70 0.90 1.10 1.30 1.50 0.50 -40 85 no load, v cc = 3.3v 40k 60k 80k supply current vs. output loading ds1090 toc03 load capacitance (pf) supply current (ma) 35 30 25 20 15 10 1 2 3 4 0 540 t a = +25 c, r set = 40k 4v 3v 5v output voltage high vs. output current ds1090 toc04 output current (ma) output voltage (v) -1 -2 -3 -4 2.8 2.9 3.0 3.1 2.7 -5 0 v cc = 3.0v output voltage low vs. output current ds1090 toc05 output current (ma) output voltage (v) 4 3 2 1 0.1 0.2 0.3 0.4 0 05 v cc = 3.0v output frequency vs. supply voltage ds1090 toc06 supply voltage (v) frequency (mhz) 5.0 4.5 4.0 3.5 5 6 7 8 9 10 4 3.0 5.5 t a = +25 c 60k 80k 40k
ds1090 low-frequency, spread-spectrum econoscillator _____________________________________________________________________ 5 output frequency vs. temperature ds1090 toc07 temperature ( c) frequency (mhz) 60 35 10 -15 5 6 7 8 9 10 4 -40 85 v cc = 3.3v 60k 80k 40k duty cycle vs. temperature ds1090 toc08 temperature ( c) duty cycle (%) 60 35 10 -15 49 50 51 52 48 -40 85 r set = 40k v cc = 3.3v v cc = 5v ds1090u-1 resistor current vs. resistor value ds1090 toc09 r set (k ) resistor current ( a) 70 60 50 10 12 14 16 18 8 40 80 v cc = 3.3v, t a = +25 c frequency error vs. supply voltage (from 3.3v) ds1090 toc10 supply voltage (v) frequency error (%) 5.0 4.5 4.0 3.5 -2.5 0 2.5 5.0 -5.0 3.0 5.5 t a = +25 c 40k 60k 80k frequency error vs. temperature (from +25 c) ds1090 toc11 temperature ( c) frequency error (%) 60 35 10 -15 -1.0 0 1.0 2.0 -2.0 -40 85 v cc = 3.3v 40k 60k 80k power spectrum vs. spread ds1090 toc12 frequency (mhz) power (dbm) 5.35 -70 -60 -50 -40 -30 -20 -10 0 -80 4.80 5.90 v cc = 3.3v, t a = +25 c, jc0 = jc1 = 1 off 2% 4% 8% typical operating characteristics (continued) (v cc = +3.3v, t a = +25?, unless otherwise noted.)
ds1090 low-frequency, spread-spectrum econoscillator 6 _____________________________________________________________________ pin description block diagram pin name function 1 out oscillator output 2r set frequency control resistor input 3v cc positive-supply terminal 4 gnd ground 5j0 6j1 dither amplitude (percentage) inputs (see table 2) 7 jc0 8 jc1 dither rate divisor inputs (see table 1) ds1090 gnd master oscillator (vco) 4mhz?8mhz factory programmed prescaler ( 1, 2, 4, 8, 16, or 32) triangle generator v cc v cc r set voltage- bias circuit out f mosc f osc f mod f out j0 j1 jc0 jc1 buffer + + dither amplitude (0, 2, 4, or 8%) dither rate ( 4, 8, 16, or 32) + - ( 128) dither generator
ds1090 low-frequency, spread-spectrum econoscillator _____________________________________________________________________ 7 detailed description the ds1090 is a center-dithered, spread-spectrum sili- con 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 8mhz can be achieved. the output center frequency can be dithered by selecting the desired dither rate and ampli- tude with discrete inputs j0, j1, jc0, and jc1. the ds1090 contains four basic circuit blocks: master oscillator, factory-programmed prescaler, dither gener- ator, and the voltage-bias circuit that provides the feed- back path to the master oscillator for frequency control and dithering functions. master oscillator the master oscillator is programmable in the applica- tion by the use of an external resistor (r set ) tied to ground (gnd). resistor values of 45k to 91k vary the square-wave output frequency of the voltage-con- trolled master oscillator (f mosc ) from 8mhz down to 4mhz (see figure 1). the master oscillator (hz) frequency can be stated as factory-programmed prescaler the prescaler divides the frequency of the master oscil- lator by 1, 2, 4, 8, 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 user- configurable divider (determines dither rate), a triangle generator, and a user-configurable dither amplitude cir- cuit (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 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 triangle- wave signal of either 1/512th, 1/1024th, 1/2048th, or 1/4096th of the master oscillator (f mod ), depending upon the user? divisor setting. the dithering frequency can be also expressed as the result of where divisor is 4, 8, 16, or 32. f f divisor mod mosc = 128 f e sistor mosc ? + 3 6461 11 . re master oscillator frequency vs. external resistor selection ds1090 fig01 r set resistance (k ) f mosc (mhz) 90 80 70 60 50 4 5 6 7 8 9 3 40 figure 1. master oscillator frequency f mosc time dither amount (2, 4, or 8%) if dither amount = 0% (- 1, 2, or 4% of f mosc ) f mod 1 (+ 1, 2, or 4% of f mosc ) programmed f mosc figure 2. center frequency dither diagram jc1 jc0 dithering percentage (f mosc /n) divisor setting 00 f mosc / 512 4 01 f mosc / 1024 8 10 f mosc / 2048 16 11 f mosc / 4096 32 table 1. dither rate divisor settings
ds1090 low-frequency, spread-spectrum econoscillator maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it 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 2007 maxim integrated products is a registered trademark of maxim integrated products. is a registered trademark of dallas semiconductor corporation. dither percentage settings dither amplitude (measured in percent from the mas- ter 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 modu- lates the master oscillator to a percentage of its resis- tor-set center frequency. this percentage is set in the end application to be 0%, 2%, 4%, or 8% (see table 2). 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 low- frequency emi-reduced clock oscillator. all control pins must be biased per tables 1 and 2 for proper operation for the individual application? 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 fre- quency 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 compo- nent with a temperature coefficient that satisfies the over- all 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 0.01? and 0.1?. use a high-quality, ceramic, surface-mount capacitor, and mount it as close as possible to the v cc and gnd pins of the ic to minimize lead inductance. j1 j0 dither percent (%) 00 0 01 2 10 4 11 8 table 2. dither percentage setting package information for the latest package outline information, go to www.maxim-ic.com/dallaspackinfo . chip information transistor count: 1883 substrate connected to ground
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