參數(shù)資料
型號: LTC6900IS5#TRMPBF
廠商: Linear Technology
文件頁數(shù): 10/12頁
文件大小: 0K
描述: IC OSC SILICON 20MHZ TSOT23-5
產(chǎn)品目錄繪圖: TSOT23-5 Series Top
標(biāo)準(zhǔn)包裝: 1
類型: 振蕩器 - 硅
頻率: 1kHz ~ 20MHz
電源電壓: 2.7 V ~ 5.5 V
電流 - 電源: 920µA
工作溫度: -40°C ~ 85°C
封裝/外殼: SOT-23-5 細(xì)型,TSOT-23-5
包裝: 標(biāo)準(zhǔn)包裝
供應(yīng)商設(shè)備封裝: TSOT-23-5
安裝類型: 表面貼裝
產(chǎn)品目錄頁面: 1715 (CN2011-ZH PDF)
其它名稱: LTC6900IS5#TRMPBFDKR
LTC6900
7
6900fa
APPLICATIONS INFORMATION
SELECTING THE DIVIDER SETTING AND RESISTOR
The LTC6900’s master oscillator has a frequency range
spanning 0.1MHz to 20MHz. However, accuracy may suffer
if the master oscillator is operated at greater than 10MHz
with a supply voltage lower than 4V. A programmable
divider extends the frequency range to greater than three
decades. Table 1 describes the recommended frequencies
for each divider setting. Note that the ranges overlap; at
some frequencies there are two divider/resistor combina-
tions 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 accurate. For instance, fOSC = 100kHz can be
obtained by either RSET = 20k, N = 100, master oscillator =
10MHz or RSET = 200k, N = 10, master oscillator = 1MHz.
The RSET = 200k approach 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 < 20kΩ),
the LTC6900 may experience 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 resistance,
a simple equation relates resistance with frequency.
RSET = 20k
10MHz
N fOSC
, N =
100
10
1
(RSETMIN = 10k, RSETMAX = 2M)
Any resistor, RSET, tolerance adds to the inaccuracy of the
oscillator, fOSC.
ALTERNATIVE METHODS OF SETTING THE OUTPUT
FREQUENCY OF THE LTC6900
The oscillator may be programmed by any method that
sources a current into the SET pin (Pin 3). The circuit in
Figure 3 sets the oscillator frequency using a programmable
current source and in the expression for fOSC, the resistor
RSET is replaced by the ratio of 1.1V/ICONTROL. As already
explained in the Operation section, the voltage difference
between V + and SET is approximately 1.1V, therefore, the
Figure 3 circuit is less accurate than if a resistor controls
the oscillator frequency.
Figure 4 shows the LTC6900 congured as a VCO. A voltage
source is connected in series with an external 20k resis-
tor. The output frequency, fOSC, will vary with VCONTROL,
that is the voltage source connected between V+ and the
SET pin. Again, this circuit decouples the relationship
between the input current and the voltage between V+
and SET; the frequency accuracy will be degraded. The
oscillator frequency, however, will monotonically increase
with decreasing VCONTROL.
Figure 3. Current Controlled Oscillator
Figure 4. Voltage Controlled Oscillator
V+
1
2
3
5
182kHz TO 18MHz (TYPICALLY ±8%)
V+
0.1μF
ICONTROL
1μA TO 100μA
6900 F03
4
GND
N = 1
LTC6900
SET
OUT
DIV
10MHz
N
OSC
ICONTROL
ICONTROL EXPRESSED IN (A)
20kΩ
1.1V
V+
1
2
3
5
V+
0.1μF
RSET
20k
VCONTROL
0V TO 1.1V
6900 F04
4
GND
N = 1
LTC6900
SET
OUT
DIV
+
10MHz
N
OSC
1 –
VCONTROL
1.1V
20k
RSET
()
TYPICAL fOSC ACCURACY
±0.5%, VCONTROL = 0V
±8%, VCONTROL = 0.5V
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