MAXIM DS1090 User Manual

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.

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

1

Pin Configuration

Ordering Information

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.

EconOscillator is a trademark of Dallas Semiconductor.

OUTPUT

PART

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+

DS1090U-16+

DS1090U-32+

FREQUENCY
RANGE

500kHz to
1MHz

250kHz to
500kHz

125kHz to
250kHz

PRE SCALER

8 8 μSOP

16 8 μSOP

32 8 μSOP

PIN­PACKAGE

V

IN

V

CC

DC-DC

STEP-DOWN

V

CC

DS1090

R

SET

45kΩ

TO 91kΩ

GND

CONVERTER

OUT

JC0

JC1

J0

J1

V

OUT

TOP VIEW

1

OUT

2

SET

V

3

CC

4

87JC1

DS1090

μSOP

JC0R

J1

6

J0GND

5

DS1090

Low-Frequency, Spread-Spectrum
EconOscillator

2 _____________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

RECOMMENDED DC OPERATING CONDITIONS

(TA= -40°C to +85°C)

DC ELECTRICAL CHARACTERISTICS

(VCC= +3.0V to +5.5V, TA= -40°C to +85°C, unless otherwise noted.)

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.

Voltage Range on VCCRelative 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

Input Logic 1 (J0, J1, JC0, JC1) V

Input Logic 0 (J0, J1, JC0, JC1) V

CC

(Note 1) 3.0 5.5 V

IH

IL

0.7 x
V

-0.3

CC

V

CC

0.3

+0.3 x

V

CC

+

V

V

Supply Current I

High-Level Output Voltage (OUT) V

Low-Level Output Voltage (OUT) V

High-Level Input Current
(J0, J1, JC0, JC1)

Low-Level Input Current
(J0, J1, JC0, JC1)

Resistor Current I

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

CC

OH

OL

I

IH

I

RES

CL = 15pF, VCC = 3.3V, R

CL = 15pF, VCC = 5.5V, R

IOH = -4mA

VCC = min

IOL = 4mA 0.4 V

VIH = V

CC

VIL = 0V -1.0 µA

IL

VCC = max 150 µA

= 40kΩ 1.4

SET

= 40kΩ 1.7 3

SET

2.4 V

mA

+1.0 µA

DS1090

Low-Frequency, Spread-Spectrum

EconOscillator

_____________________________________________________________________ 3

AC ELECTRICAL CHARACTERISTICS

(VCC= +3.0V to +5.5V, TA= -40°C to +85°C, 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.

Internal Master Oscillator
Frequency

Output Frequency Tolerance f

Voltage Frequency Variation f

Temperature Frequency Variation f

Peak-to-Peak Dither (3)
(Note 5)

Power-Up Time

Load Capacitance CL (Note 7) 30 pF

Output Duty Cycle

Output Rise/Fall Time tR, tF CL = 15pF 20 ns

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

f

MOSC

OUT

OUT

OUT

t

POR

t

STAB

4.0 8.0 MHz

VCC = 3.3V,
T

= +25°C

A

TA = +25°C, R

= 3.0V to 3.6V (Notes 2, 3)

V

CC

TA = +25°C, R
V

= 4.5V to 5.5V (Notes 2, 3)

CC

VCC = 3.3V
(Notes 2, 3, 4)

J0 = GND, J1 = GND 0

J0 = VCC, J1 = GND 2

J0 = GND, J1 = VCC 4

J0 = V

+

(Note 6) 0.1 0.5 ms

4MHz to 8MHz, TA = +25°C (Note 3) 45 55

<4MH z (Note 4) 50

, J1 = VCC 8

CC

SET

SET

= 60k,

= 60k,

-3.0 +3.0 %

-0.5 +0.5

%

-1.25 +1.25

-2.0 +2.0 %

%

%

DS1090

Low-Frequency, Spread-Spectrum
EconOscillator

4 _____________________________________________________________________

Typical Operating Characteristics

(VCC= +3.3V, TA = +25°C, unless otherwise noted.)

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

DS1090 toc01

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (mA)

5.04.54.03.5

0.95

1.20

1.45

1.70

0.70

3.0 5.5

NO LOAD, TA = +25°C

40kΩ

60kΩ

80kΩ

SUPPLY CURRENT

vs. TEMPERATURE

DS1090 toc02

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

603510-15

0.70

0.90

1.10

1.30

1.50

0.50

-40 85

NO LOAD, VCC = 3.3V

40kΩ

60kΩ

80kΩ

SUPPLY CURRENT

vs. OUTPUT LOADING

DS1090 toc03

LOAD CAPACITANCE (pF)

SUPPLY CURRENT (mA)

353025201510

1

2

3

4

0

540

TA = +25°C, R

SET

= 40kΩ

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

VCC = 3.0V

OUTPUT VOLTAGE LOW

vs. OUTPUT CURRENT

DS1090 toc05

OUTPUT CURRENT (mA)

OUTPUT VOLTAGE (V)

4321

0.1

0.2

0.3

0.4

0

05

VCC = 3.0V

OUTPUT FREQUENCY

vs. SUPPLY VOLTAGE

DS1090 toc06

SUPPLY VOLTAGE (V)

FREQUENCY (MHz)

5.04.54.03.5

5

6

7

8

9

10

4

3.0 5.5

TA = +25°C

60kΩ

80kΩ

40kΩ

DS1090

Low-Frequency, Spread-Spectrum

EconOscillator

_____________________________________________________________________

5

Typical Operating Characteristics (continued)

(VCC= +3.3V, TA = +25°C, unless otherwise noted.)

OUTPUT FREQUENCY

10

9

8

7

FREQUENCY (MHz)

6

5

4

-40 85

5.0

2.5

0

FREQUENCY ERROR (%)

-2.5

-5.0

3.0 5.5

vs. TEMPERATURE

VCC = 3.3V

40kΩ

60kΩ

80kΩ

603510-15

TEMPERATURE (°C)

FREQUENCY ERROR

vs. SUPPLY VOLTAGE (FROM 3.3V)

TA = +25°C

80kΩ

40kΩ

SUPPLY VOLTAGE (V)

60kΩ

5.04.54.03.5

DS1090 toc07

DUTY CYCLE (%)

DS1090 toc10

FREQUENCY ERROR (%)

-1.0

-2.0

DUTY CYCLE

vs. TEMPERATURE

52

51

50

49

48

-40 85

VCC = 5V

DS1090U-1

TEMPERATURE (°C)

VCC = 3.3V

R

SET

= 40kΩ

603510-15

FREQUENCY ERROR

vs. TEMPERATURE (FROM +25°C)

2.0

VCC = 3.3V

1.0

0

-40 85
TEMPERATURE (°C)

60kΩ

40kΩ

603510-15

80kΩ

DS1090 toc08

DS1090 toc11

RESISTOR CURRENT
vs. RESISTOR VALUE

18

16

14

12

RESISTOR CURRENT (μA)

10

8

40 80

VCC = 3.3V, TA = +25°C

R

(kΩ)

SET

POWER SPECTRUM vs. SPREAD

0

OFF

-10

-20
±2%

-30

±4%

-40
±8%

POWER (dBm)

-50

-60

-70

-80

4.80 5.90
FREQUENCY (MHz)

5.35

VCC = 3.3V,
T
JC0 = JC1 = 1

706050

= +25°C,

A

DS1090 toc09

DS1090 toc12

DS1090

Low-Frequency, Spread-Spectrum
EconOscillator

6 _____________________________________________________________________

Pin Description

Block Diagram

PIN NAME FUNCTION

1 OUT Oscillator Output

2R

3VCCPositive-Supply Terminal

4 GND Ground

5J0

6J1

7 JC0

8 JC1

Frequency Control Resistor Input

SET

Dither Amplitude (Percentage) Inputs
(see Table 2)

Dither Rate Divisor Inputs (see Table 1)

R

SET

V

GND

JC0

JC1

VOLTAGE-

BIAS CIRCUIT

DITHER

MASTER

OSCILLATOR

(VCO)

4MHz–8MHz

f

DITHER GENERATOR

MOD

f

MOSC

TRIANGLE

GENERATOR

(÷ 128)

+

∑

+

V

CC

CC

+

­AMPLITUDE

(0, 2, 4, OR 8%)

J0

J1

DS1090

FACTORY

PROGRAMMED

PRESCALER

(÷ 1, 2, 4, 8, 16, OR 32)

DITHER RATE

(÷ 4, 8, 16, OR 32)

f

OSC

BUFFER

f

OUT

OUT

DS1090

Low-Frequency, Spread-Spectrum

EconOscillator

_____________________________________________________________________ 7

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.

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 45kΩ to 91kΩ vary
the square-wave output frequency of the voltage-con­trolled 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 oscil­lator by 1, 2, 4, 8, 16, or 32 to generate the square­wave 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 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

where Divisor is 4, 8, 16, or 32.

Figure 1. Master Oscillator Frequency

Figure 2. Center Frequency Dither Diagram

Table 1. Dither Rate Divisor Settings

MASTER OSCILLATOR FREQUENCY vs.

EXTERNAL RESISTOR SELECTION

9

8

7

(MHz)

6

MOSC

f

5

4

3

50

40

R

RESISTANCE (kΩ)

SET

80

7060

DS1090 fig01

90

E

+3 6461 11.

f

MOSC

≅

Re

sistor

(+ 1, 2, or 4% of f

Programmed f

(- 1, 2, or 4% of f

MOSC

MOSC

MOSC

)

)

MOSC

f

f

1

MOD

IF DITHER AMOUNT = 0%

DITHER
AMOUNT
(2, 4, OR 8%)

TIME

f

=

Divisor

MOSC

× 128

f

MOD

JC1 JC0

00 F

01 F

10 f

11 f

DITHERING PERCENTAGE

(f

MOSC

MOSC

MOSC

MOSC

MOSC

/n)

/ 512 4

/ 1024 8

/ 2048 16

/ 4096 32

DIVISOR

SETTING

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 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

© 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 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).

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. 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 0.01µF
and 0.1µF. 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.

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

J1 J0 DITHER PERCENT (%)

00 0

01 2

10 4

11 8