LTC6900CS5 datasheet(10/12 Pages) LINER

10 / 12 page

LTC6900

6900f

APPLICATIO S I FOR ATIO

Once RIN/RSET is known, calculate RSET from:

MHz

SET

OSC MAX

IN MAX

RES

SET

RES

SET

−

()++





























••

()

(3)

Example 1:

In this example, the oscillator output frequency has small

excursions. This is useful where the frequency of a system

should be tuned around some nominal value.

Let V+ = 3V, fOSC(MAX) = 2MHz for VIN(MAX) = 3V and

fOSC(MIN) = 1.5MHz for VIN = 0V. Solve for RIN/RSET by

Equation (2), yielding RIN/RSET = 9.9/1. RSET = 110.1k by

Equation (4). RIN = 9.9RSET = 1.089M. For standard

resistor values, use RSET = 110k (1%) and RIN = 1.1M

(1%). Figure 10 shows the measured fOSC vs VIN. The

1.5MHz to 2MHz frequency excursion is quite limited, so

the curve of fOSC vs VIN is linear.

Example 2:

Vary the oscillator frequency by one octave per volt.

Assume fOSC(MIN) = 1MHz and fOSC(MAX) = 2MHz, when the

input voltage varies by 1V. The minimum input voltage is

half supply, that is VIN(MIN) = 1.5V, VIN(MAX) = 2.5V and

V+ = 3V.

Equation (2) yields RIN/RSET = 1.273 and Equation (3)

yields RSET = 142.8k. RIN = 1.273RSET = 181.8k. For

standard resistor values, use RSET = 143k (1%) and RIN =

182k (1%). Figure 11 shows the measured fOSC vs VIN. For

VIN higher than 1.5V, the VCO is quite linear; nonlinearities

occur when VIN becomes smaller than 1V, although the

VCO remains monotonic.

Maximum VCO Modulation Bandwidth

The maximum VCO modulation bandwidth is 25kHz; that

is, the LTC6900 will respond to changes in VIN at a rate up

to 25kHz. In lower frequency applications however, the

modulation frequency may need to be limited to a lower

rate to prevent an increase in output jitter. This lower limit

is the master oscillator frequency divided by 20, (fOSC/20).

In general, for minimum output jitter the modulation

frequency should be limited to fOSC/20 or 25kHz, which-

ever is less. For best performance at all frequencies, the

value for fOSC should be the master oscillator frequency

(N = 1) when VIN is at the lowest level.

VIN (V)

0.5

1.5

2.5

6900 F10

2.00

1.95

1.90

1.85

1.80

1.75

1.70

1.65

1.60

1.55

1.50

RIN = 1.1M

RSET = 110k

V+ = 3V

N = 1

VIN (V)

0.5

1.5

2.5

6900 F11

3000

2500

2000

1500

1000

500

RIN = 182k

RSET = 143k

V+ = 3v

N = 1

Figure 11. Output Frequency vs Input Voltage

Figure 10. Output Frequency vs Input Voltage

LTC6900CS5 датащи(PDF) 10 Page - Linear Technology

LTC6900CS5 датащи(HTML) 10 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12

датащи скачать

ссылки URL