 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC6990CS6PBF Datasheet(PDF) 15 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC6990CS6PBF Datasheet(HTML) 15 Page - Linear Technology |
|
|
15 / 28 page  LTC6990 15 6990f APPLICATIONS INFORMATION Start-Up Behavior When first powered up, the output is high impedance. If the output is enabled (OE = 1) at the end of the start-up time, the output will go low for one tMASTER cycle (or half a tOUT cycle if NDIV < 4) before the first rising edge. If the output is disabled (OE = 0) at the end of the start-up time, the output will drop to a low output if the Hi-Z bit = 0, or simply remain floating if Hi-Z = 1. Basic Fixed Frequency Operation The simplest and most accurate method to program the LTC6990 for fixed frequency operation is to use a single resistor, RSET, between the SET and GND pins. The design procedure is a simple two step process. First select the NDIV value and then calculate the value for the RSET resistor. Step 1: Selecting the NDIV Frequency Divider Value As explained earlier, the voltage on the DIV pin sets the DIVCODE which determines both the Hi-Z bit and the NDIV value. For a given output frequency, NDIV should be selected to be within the following range. 62.5kHz fOUT ≤ NDIV ≤ 1MHz fOUT (1a) To minimize supply current, choose the lowest NDIV value (generally recommended). For faster start-up or decreased jitter, choose a higher NDIVsetting.Alternatively,useTable1 as a guide to select the best NDIV value for the given ap- plication. After choosing the value for NDIV, use Table 1 to select the proper resistor divider or VDIV/V+ ratio to apply to the DIV pin. Step 2: Calculate and Select RSET The final step is to calculate the correct value for RSET using the following equation. RSET = 1MHz • 50k NDIV •fOUT (1b) Select the standard resistor value closest to the calculated value. Example: Design a 20kHz Oscillator with Minimum Power Consumption Step 1: Selecting the NDIV Frequency Divider Value First, choose an NDIV value that meets the requirements of Equation (1a). 3.125 ≤ NDIV ≤ 50 Potential settings for NDIV include 4, 8, 16, and 32. NDIV = 4 is the best choice, as it minimizes supply current by using a large RSET resistor. Using Table 1, choose the R1 and R2 values to program DIVCODE to either 2 or 13, depending on the desired behavior when the output is disabled. Step 2: Select RSET Calculate the correct value for RSET using Equation (1b). RSET = 1MHz • 50k 4 • 20kHz = 625k Since 625k is not available as a standard 1% resistor, substitute 619k if a 0.97% frequency shift is acceptable. Otherwise, select a parallel or series pair of resistors such as 309k and 316k to attain a more precise resistance. Frequency Modulated Operation (Voltage-Controlled Oscillator) Operating the LTC6990 as a voltage-controlled oscillator in its simplest form is achieved with one additional resistor. As shown in Figure 11, voltage VCTRL sources/sinks a current through RVCO to vary the ISET current, which in turn modu- lates the output frequency as described in Equation (2). fOUT = 1MHz • 50k NDIV •RVCO •1+ RVCO RSET − VCTRL VSET ⎛ ⎝⎜ ⎞ ⎠⎟ (2) Figure 11. Voltage Controlled Oscillator 6990 F08 LTC6990 OE GND SET OUT V+ DIV C1 0.1μF R1 R2 RSET V+ V+ RVCO VCTRL |
Similar Part No. - LTC6990CS6PBF |
|
Similar Description - LTC6990CS6PBF |
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
