Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsLinear ICsLTC6909CMS#PBF

LTC6909

6909fa

Synchronizing Multiple Switching Power Supplies

ApplicAtions

L, LT, LTC, LTM, Linear Technology, the Linear logo and µModule are registered trademarks

and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners. Protected by U.S. Patents including 6342817, 6614313,

7417509.

1 to 8 Output, Multiphase

Silicon Oscillator with Spread

Spectrum Modulation

The LTC

6909 is an easy to use precision oscillator that

can provide 1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-phase synchro-

nized outputs. The LTC6909 also offers spread spectrum

frequency modulation (SSFM), which can be enabled to im-

prove electromagnetic compatibility (EMC) performance.

Eight separate outputs provide up to eight rail-to-rail,

50% duty cycle clock signals. Using three logic inputs, the

outputs are configured for phase separation, ranging from

45° to 120° (three to eight phases). The clock outputs can

also be held low or configured for Hi-Z. A single resistor,

combined with the phase configuration, sets the output

frequency, based on the following formula:

OUT

= 20MHz • 10k/(R

SET

• PH)

where PH = 3, 4, 5, 6, 7 or 8

The LTC6909 can be used in applications requiring only

one or two output phases. Alternatively, the LTC6908

family of parts provides the same two output signals but

in a smaller SOT-23 or 2mm × 3mm DFN package. The

LTC6908-1 provides complimentary (180°) outputs while

the LTC6908-2 provides quadrature (90°) outputs.

1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-Phase Outputs

One External Resistor Sets the Output Frequency

from 12.5kHz to 6.67MHz

Optional Spread Spectrum Frequency for Improved

EMI Performance

±10% Frequency Spreading

Outputs Can Be Held Low or Floated (Hi-Z)

Three Spread Spectrum Modulation Rates

OUT

/16, f

OUT

/32 and f

OUT

/64

400µA Supply Current

Operates from a Single 2.7V to 5.5V Supply

Fast Start-Up Time

First Cycle Accurate

Outputs Are High Impedance Until Frequency Settles

MS16 Package

typicAl ApplicAtion

FeAtures Description

Providing a 4-Phase Synchronizing Clock to LTM Modules

LTC6909

10V TO 14V

0.1µF

71.5k

0.1µF

0.01µF

ENABLE SSFM DISABLE SSFM

LTM4601

INTV

LTM4601-1

TRACKING

S0FT-START

1.5V

48A

TRACKING

6909 TA01

GND

SET

PH0

PH1

PH2

MOD

OUT1

OUT2

OUT3

OUT4

OUT5

OUT6

OUT7

OUT8

FREQUENCY

(FUNDAMENTAL AND HARMONICS SHOWN)

150kHz

OUTPUT (dBc) OUTPUT (dBc)

–20

–10

6909 TA01b

–30

–40

–50

30MHz

–20

–10

–30

–40

–50

SSFM DISABLED

SSFM ENABLED

SSFM = f

OUT

/32

150kHz to 30MHz Output

Frequency Spectrum

(9kHz Res BW)

Summary of content (22 pages)

PAGE 1
LTC6909 1 to 8 Output, Multiphase Silicon Oscillator with Spread Spectrum Modulation Description Features n n n n n n n n n n n n 1-, 2-, 3-, 4-, 5-, 6-, 7- or 8-Phase Outputs One External Resistor Sets the Output Frequency from 12.5kHz to 6.67MHz Optional Spread Spectrum Frequency for Improved EMI Performance ±10% Frequency Spreading Outputs Can Be Held Low or Floated (Hi-Z) Three Spread Spectrum Modulation Rates fOUT/16, fOUT/32 and fOUT/64 400µA Supply Current Operates from a Single 2.7V to 5.
PAGE 2
LTC6909 Absolute Maximum Ratings Pin Configuration (Note 1) Supply Voltage (V+A) to GND.......................................6V Supply Voltage (V+D) to GND.......................................6V Maximum Voltage on Any Pin................. (GND – 0.3V) ≤ VPIN ≤ (V+ + 0.3V) Operating Temperature Range (Note 2) LTC6909C.............................................–40°C to 85°C LTC6909I..............................................–40°C to 85°C LTC6909H...........................................
PAGE 3
LTC6909 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C or as noted. Test conditions are V+ = V+A = V+D = 2.7V to 5.5V, RL = 5k, CL = 5pF unless otherwise noted. The modulation is turned off (MOD is connected to OUT1) and PH = 8 unless otherwise specified. RSET is defined as the resistor connected from the SET pin to the V+A pin.
PAGE 4
LTC6909 Electrical Characteristics Note 4: fMASTER is the internal master oscillator frequency. The output frequency is fMASTER/PH. The PH value is determined by the connections of the PH0, PH1 and PH2 pins as described in the Applications Information section. Note 5: Frequency accuracy is defined as the deviation from the fOUT equation. fMASTER = 20MHz • 10k/RSET, fOUT = 20MHz • 10k/(RSET • PH), PH = 3, 4, 5, 6, 7 or 8. Note 6: Guaranteed by 5V test.
PAGE 5
LTC6909 Typical Performance Characteristics Typical Output Resistance vs Supply Voltage Supply Current vs Temperature 110 700 600 550 V+ = 2.7V 500 RSET = 100k PH = 3 CLOAD = 5pF SSFM DISABLED 450 20 40 60 80 TEMPERATURE (°C) 90 80 70 60 50 40 20 3.0 RISE TIME 2.5 2.0 1.5 FALL TIME 1.0 0.5 30 100 120 CLOAD = 5pF 4.0 TA = 25°C RLOAD = 5k 3.5 0 2.7 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 SUPPLY VOLTAGE (V) 3.2 3.7 4.2 4.7 SUPPLY VOLTAGE (V) 5.
PAGE 6
LTC6909 Pin Functions V+A (Pin 1): Analog Voltage Supply (2.7V ≤ V+A ≤ 5.5V). This supply should be kept free of noise and ripple. It should be bypassed directly to GND with a 0.1µF or greater low ESR capacitor. V+A and V+D must be connected to the same supply voltage. GND (Pin 2): Ground Connections. Should be tied to a ground plane for best performance. PH0, PH1, PH2 (Pins 3, 4, 15): Output Phasing Selection Pins.
PAGE 7
LTC6909 Block Diagram PH0 PH1 PH2 3 4 15 V+A I fMASTER = 20MHz • 10k • +MASTER = 20MHz • 10k/RSET V – VSET (SSFM = OFF) MASTER OSCILLATOR DRIVER 5 OUT1 DRIVER 6 OUT2 DRIVER 7 OUT3 DRIVER 8 OUT4 DRIVER 9 OUT5 IREF DRIVER 10 OUT6 MDAC DRIVER 11 OUT7 DRIVER 12 OUT8 + 1 RSET SET V+D 13 VSET 16 VBIAS V OUT – ISET = V+ – VSET RSET V+ DETECT CLOCK INPUT + – POR OUTPUT Hi-Z UNTIL STABLE DIVIDE BY 16/32/64 3-STATE INPUT DECODER MOD 14 OUTPUT PHASING DRIVERS IMASTER PSEUDORANDOM
PAGE 8
LTC6909 Operation As shown in the Block Diagram, the LTC6909’s master oscillator is controlled by the ratio of the voltage between the V+A and SET pins and the current entering the SET pin (IMASTER). When the spread spectrum frequency modulation (SSFM) is disabled, IMASTER is strictly determined by the (V+A – VSET) voltage and the RSET resistor. When SSFM is enabled, IMASTER is modulated by a filtered pseudorandom noise (PRN) signal.
PAGE 9
LTC6909 Operation MASTER OSCILLATOR PH2 - PH1 - PH0 = 000 PH2 - PH1 - PH0 = 001 PH2 - PH1 - PH0 = 010 ALL OUTPUTS ARE Hi-Z ALL OUTPUTS ARE LOW PH = 3, fOUTPUT = fMASTER/3 ADJACENT OUTPUTS ARE PHASE SHIFTED BY 120° PH = 4, fOUTPUT = fMASTER/4 ADJACENT OUTPUTS ARE PHASE SHIFTED BY 90° PH = 5, fOUTPUT = fMASTER/5 ADJACENT OUTPUTS ARE PHASE SHIFTED BY 72° PH = 6, fOUTPUT = fMASTER/6 ADJACENT OUTPUTS ARE PHASE SHIFTED BY 60° OUT1 OUT2 OUT3 OUT4 Hi-Z OUT5 Hi-Z OUT6 Hi-Z OUT7 Hi-Z OUT8 Hi-Z PH2 - PH1 - PH
PAGE 10
LTC6909 Operation MASTER OSCILLATOR PH2 - PH1 - PH0 = 110 PH = 7, fOUTPUT = fMASTER/7 ADJACENT OUTPUTS ARE PHASE SHIFTED BY 51.43° PH = 8, fOUTPUT = fMASTER/8 ADJACENT OUTPUTS ARE PHASE SHIFTED BY 45° OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 OUT7 OUT8 Hi-Z PH2 - PH1 - PH0 = 111 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6 OUT7 OUT8 6909 F02b Figure 2b.
PAGE 11
LTC6909 Operation is generated by a linear feedback shift register that is 15 bits long. The pseudorandom sequence will repeat every (215 – 1) • N clock cycles. This guarantees a repetition rate below 13Hz for output frequencies up to 6.67MHz. Seven bits of the shift register are sent in parallel to the MDAC which produces the modulating current waveform.
PAGE 12
LTC6909 Applications Information Selecting The Frequency-Setting Resistor The LTC6909 has a master oscillator frequency range spanning 100kHz to 20MHz depending on the RSET resistor value. However, accuracy may suffer if the oscillator is operated at a master oscillator frequency greater than 10MHz with a supply voltage lower than 4V. With a linear correspondence between the master oscillator period and the RSET resistance, a simple equation relates resistance with frequency.
PAGE 13
LTC6909 Applications Information transitions have been slowed and the corners rounded by a first order lowpass filter with a corner frequency set to the modulation rate (fOUT/N), where N is the modulation rate divider setting, which is determined by the state of the MOD pin. This filtered modulating signal may be acceptable for many logic systems but the cycle-to-cycle jitter issues must be considered carefully.
PAGE 14
LTC6909 Applications Information peak electromagnetic radiation (or conduction) is reduced. Output ripple may be somewhat increased, but its behavior is very much like noise and its system impact is benign. SUPPLY BYPASSING, SIGNAL CONNECTIons AND PCB LAYOUT Using the LTC6909 in spread spectrum mode naturally eliminates any concerns for output frequency accuracy and stability as it is continually hopping to new settings.
PAGE 15
LTC6909 Applications Information To assist in an orderly start-up sequence, the LTC6909’s outputs are in a high impedance state for the first 128 master clock cycles after power-up. This ensures that the first clock cycle is very close to the desired operating frequency. Powering up and down complex multiphase switching regulator circuits is always chaotic and can have serious system consequences if it is not done carefully.
PAGE 16
LTC6909 Applications Information high impedance) and 001 (all outputs are low) are useful for controlling the clocking of switching regulators during start-up. At start-up, most switching regulators ignore the clock input until a power good state is achieved. Nearly all of Linear Technology’s switching regulators operate in this manner. However, some switching regulators from other vendors do not ignore the clock input on start-up and yet are not synchronizable until the power good state is reached.
PAGE 17
LTC6909 Typical Applications Simply Parallel Multiple DC/DC µModule® Regulator Systems to Achieve Higher Output Current. Board Layout Is as Easy as Copying and Pasting Each µModule Regulator’s Layout With Very Few External Components Required CLOCK SYNC 0° PHASE VIN 10V TO 14V 51.1k + 0.1µF LTC6909 V+A SET GND PH2 PH0 PH1 OUT1 OUT2 OUT3 OUT4 MOD V+D OUT8 OUT7 OUT6 OUT5 392k PLLIN TRACK/SS VOUT VIN PGOOD MPGM RUN COMP INTVCC DRVCC CIN* 100µF 25V 10µF 25V ×2 71.5k 51.
PAGE 18
LTC6909 Typical applications Using Additional Standard Logic Inverters to Achieve 10- and 14-Phase Outputs (Inverters Are 74HC04 or Equivalent) 10 OUTPUT PHASES (OUTPUTS SHIFTED BY 36 DEGREES) 0.1µF 0.1µF 14 OUTPUT PHASES (OUTPUTS SHIFTED BY 25.71 DEGREES) V+ LTC6909 OUT1 V+D RSET 0.1µF V+ 0° (360°) LTC6909 OUT1 V+D 0° (360°) GND OUT2 180° GND OUT2 180° V+A OUT3 72° V+A OUT3 51.43° SET OUT4 252° SET OUT4 231.43° PH0 OUT5 144° PH0 OUT5 102.
PAGE 19
LTC6909 Typical applications Combining Eight Outputs With a Lowpass Filter to Create a Sine Wave 2.7V TO 5.5V 249k 1 0.1µF 2 3 4 V+A SET GND PH2 LTC6909 PH0 16 500mV/DIV 15 MOD 14 V+D 13 PH1 0.1µF 787k 5 402k 6 140k 7 80.6k 8 1 OPEN 2 3 4 21k 5 6 7 0.1µF 8 OUT1 OUT8 OUT2 OUT7 OUT3 OUT6 OUT4 OUT5 V+ LP SA LTC1563-2 NC INVA LPB NC INVB NC NC LPA SB AGND NC V– EN 787k 12 V+ = 5V THD = 0.2% 11 402k 2µs/DIV 6909 TA06 10 140k 9 80.6k 16 0.
PAGE 20
LTC6909 Package Description MS Package 16-Lead Plastic MSOP Package (Reference LTCMS DWG # 05-08-1669 Rev Ø) 16-Lead Plastic MSOP (Reference LTC DWG # 05-08-1669 Rev Ø) 0.889 ± 0.127 (.035 ± .005) 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 4.039 ± 0.102 (.159 ± .004) (NOTE 3) 0.50 (.0197) BSC 0.305 ± 0.038 (.0120 ± .0015) TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) DETAIL “A” 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) 0° – 6° TYP 0.280 ± 0.076 (.011 ± .
PAGE 21
LTC6909 Revision History REV DATE DESCRIPTION PAGE NUMBER A 1/11 Revised typical value for ∆fMASTER, 10MHz ≤ fMASTER ≤ 20MHz to ±2.7. 2 Revised Typical Applications drawings for 10 and 14 output phases. 18 6909fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 22
LTC6909 Typical Application Providing an 8-Phase Synchronizing Clock to LTM Modules INPUT SUPPLY INTVCC 0.1µF LTM4601 LTC6909 OUT1 V+D 35.7k 0.