LTC1799CS5 datasheet(4/4 Pages) LINER

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LTC1799

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408)432-1900 q FAX:(408)434-0507 q www.linear-tech.com

©LINEAR TECHNOLOGY CORPORATION 2001

1799i LT/TP 0101 2K • PRINTED IN USA

PACKAGE DESCRIPTIO

Dimensions in inches (millimeters) unless otherwise noted.

APPLICATIO S I FOR ATIO

Selecting the Divider Setting and Resistor

The LTC1799’s master oscillator has a frequency range

spanning 0.1MHz to 30MHz. However, accuracy may

suffer if the master oscillator is operated at greater than

10MHz with a supply voltage lower than 4V. A program-

mable divider extends the frequency range to greater than

three decades. Table 1 describes the recommended fre-

quencies for each divider setting. Note that the ranges

overlap; at some frequencies there are two divider/resistor

combinations that result in the desired frequency.

In general, any given oscillator frequency (fOSC) should be

obtained using the lowest master oscillator frequency.

Lower master oscillator frequencies use less power and

are more accuate. For instance, fOSC = 100kHz can be

obtained by either RSET = 10k, N = 100, master oscillator

= 10MHz or RSET = 100k, N = 10, master oscillator = 1MHz.

The RSET = 100k is preferred for lower power and better

accuracy.

Table 1. Frequency Range vs Divider Setting

DIVIDER SETTING

FREQUENCY RANGE

÷1

⇒

DIV (Pin 4) = GND

> 500kHz*

÷10

⇒

DIV (Pin 4) = Floating

50kHz to 1MHz

÷100 ⇒

DIV (Pin 4) = V+

< 100kHz

*At master oscillator frequencies greater than 10MHz (RSET < 10kΩ), the

LTC1799 may suffer reduced accuracy with a supply voltage less than 4V.

After choosing the proper divider setting, determine the

correct frequency-setting resistor. Because of the linear

correspondence between oscillation period and resis-

tance, a simple equation relates resistance with frequency.

RSET = 10k • [10MHz/(N • fOSC)], N = 1, 10, 100

(RSETMIN = 3.32k (5V Supply), 5k (3V Supply),

RSETMAX = 1M)

Any resistor, RSET, tolerance adds to the inaccuracy of the

oscillator, fOSC.

Settling Time

The settling time is proportional to RSET and is approxi-

mately tSETTLE ≈ RSET • (5µs/kΩ). This parameter is

guaranteed by design and not 100% tested.

1.50 – 1.75

(0.059 – 0.069)

0.35 – 0.55

(0.014 – 0.022)

0.35 – 0.50

(0.014 – 0.020)

FIVE PLACES (NOTE 2)

S5 SOT-23 0599

0.90 – 1.45

(0.035 – 0.057)

0.90 – 1.30

(0.035 – 0.051)

0.00 – 0.15

(0.00 – 0.006)

0.09 – 0.20

(0.004 – 0.008)

(NOTE 2)

2.60 – 3.00

(0.102 – 0.118)

NOTE:

1. DIMENSIONS ARE IN MILLIMETERS

2. DIMENSIONS ARE INCLUSIVE OF PLATING

3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR

4. MOLD FLASH SHALL NOT EXCEED 0.254mm

5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)

0.95

(0.037)

REF

2.80 – 3.00

(0.110 – 0.118)

(NOTE 3)

1.90

(0.074)

REF

S5 Package

5-Lead Plastic SOT-23

(LTC DWG # 05-08-1633)

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