收藏本站
LTC6909
11
6909fa
Spread Spectrum Frequency Modulation
The LTC6909 can operate with spread spectrum frequency
modulation(SSFM).Inthismode,theoscillator’sfrequency
is modulated by a pseudorandom noise (PRN) signal
to spread the oscillator’s energy over a wide frequency
band. This spreading decreases the peak electromagnetic
radiationlevelsandimproveselectromaneticcompatibility
(EMC) performance.
Theamountoffrequencyspreadingisfixedat20%(±10%),
where frequency spreading is defined as:
Frequency Spreading (in %) = 100 (fMAX – fMIN)/fOUT
The IMASTER current is a dynamic signal generated by
a multiplying digital-to-analog converter (MDAC) refer-
enced to ISET and lowpass filtered. IMASTER varies in a
psuedorandom noise-like manner between 0.9 ISET and
1.1 ISET. This causes the output frequency to vary in a
pseudorandom noise-like manner between 0.9 fOUT and
1.1 fOUT.
To disable the SSFM, connect one of the active outputs
to the MOD pin. An AC detector circuit shuts down the
modulation circuitry if a frequency in the vicinity of the
output frequency is detected at the MOD pin.
As stated previously, the modulating waveform is a pseu-
dorandomnoise-likewaveform.Thepseudorandomsignal
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.
Being a digitally generated signal, the output of the MDAC
is not a perfectly smooth waveform, but consists of (27)
discrete steps that change every shift register clock cycle.
Note that the shift register clock is the output frequency,
fOUT, divided by N, where N is the modulation rate divider
setting, which is determined by the state of the MOD pin.
The MOD pin should be tied to ground for the N = 16 set-
ting. Floating the MOD pin selects N = 32. The MOD pin
should be tied to V+ for the N = 64 setting.
The output of the MDAC is then filtered by a lowpass filter
withacornerfrequencysettothemodulationrate(fOUT/N).
This limits the rate of frequency change and softens the
corners of the frequency control signal, but allows the
waveform to fully settle at each frequency step. The rise
and fall times of this single pole filter are approximately
0.35/fCORNER. This is beneficial for clocking switching
regulators, as discussed in the Applications Information
section. Figure 3 illustrates how the output frequency
varies over time.
Figure 3
operAtion
tREPEAT = ((215 – 1) N)/fOUT
tSTEP = N/fOUT
fOUT + 10%
128 STEPS
tREPEAT
tSTEP
fOUT – 10%
TIME
FREQUENCY
6909 F03
发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

*型号 *数量 厂商 批号 封装
添加更多采购

我的联系方式

*
*
*
相关PDF资料
LTC6990MPS6#TRPBF IC VCO CONFIG GAIN/VOLT TSOT23-6
LTC6991MPS6#TRPBF IC OSCILLATOR RESET LF TSOT23-6
LTC6992MPS6-4#TRPBF IC OSC PWM VOLT CTLR TSOT23-6
LTC6994CDCB-2#TRPBF IC DELAY LINE 6-DFN
LTC7541ABN#PBF IC CMOS D/A CONV 12BIT 18-DIP
LTC7545ACG#TRPBF IC D/ACONV MULTIPLY 12BIT 20SSOP
LTC8043EN8 IC D/A CONV 12BIT SERIAL 8-DIP
LTC8143ESW#TRPBF IC D/A CONV 12BIT SERIAL 16-SOIC
相关代理商/技术参数
LTC6909HMS-PBF 制造商:LINER 制造商全称:Linear Technology 功能描述:1 to 8 Output, Multiphase Silicon Oscillator with Spread Spectrum Modulation
LTC6909HMS-TRPBF 制造商:LINER 制造商全称:Linear Technology 功能描述:1 to 8 Output, Multiphase Silicon Oscillator with Spread Spectrum Modulation
LTC6909IMS#PBF 功能描述:IC OSC SILICON 6.67MHZ 16-MSOP RoHS:是 类别:集成电路 (IC) >> 时钟/计时 - 可编程计时器和振荡器 系列:- 标准包装:3,000 系列:- 类型:振荡器 - 晶体 计数:- 频率:- 电源电压:2.3 V ~ 5.5 V 电流 - 电源:1.07mA 工作温度:-30°C ~ 80°C 封装/外壳:SOT-665 包装:带卷 (TR) 供应商设备封装:SS迷你型-5D 安装类型:表面贴装 其它名称:AN8955SSMTXLTR
LTC6909IMS#TRPBF 功能描述:IC OSC SILICON 6.67MHZ 16-MSOP RoHS:是 类别:集成电路 (IC) >> 时钟/计时 - 可编程计时器和振荡器 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:45 系列:- 类型:温度 - 补偿晶体振荡器（TCXO） 计数:- 频率:25MHz 电源电压:3.135 V ~ 3.465 V 电流 - 电源:1.5mA 工作温度:-40°C ~ 85°C 封装/外壳:16-SOIC（0.295"，7.50mm 宽） 包装:管件 供应商设备封装:16-SOIC W 安装类型:表面贴装
LTC6909IMS-PBF 制造商:LINER 制造商全称:Linear Technology 功能描述:1 to 8 Output, Multiphase Silicon Oscillator with Spread Spectrum Modulation
LTC6909IMS-TRPBF 制造商:LINER 制造商全称:Linear Technology 功能描述:1 to 8 Output, Multiphase Silicon Oscillator with Spread Spectrum Modulation
LTC690C 制造商:LINER 制造商全称:Linear Technology 功能描述:Microprocessor Supervisory Circuits
LTC690CN8 功能描述:IC MPU SUPERVISORY CIRCUIT 8-DIP RoHS:否 类别:集成电路 (IC) >> PMIC - 监控器 系列:- 标准包装:1 系列:- 类型:简单复位/加电复位 监视电压数目:1 输出:开路漏极或开路集电极 复位:高有效 复位超时:- 电压 - 阀值:1.8V 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:6-TSOP（0.059"，1.50mm 宽）5 引线 供应商设备封装:5-TSOP 包装:剪切带 (CT) 其它名称:NCP301HSN18T1GOSCT