Electronic Components Datasheet Search |
|
LT1715 Datasheet(PDF) 11 Page - Linear Technology |
|
LT1715 Datasheet(HTML) 11 Page - Linear Technology |
11 / 16 page 11 LT1715 APPLICATIONS INFORMATION With this in mind, calculation of the resistor values needed is a two-step process. First, calculate the value of R3 based on the additional hysteresis desired, the output voltage swing and the impedance of the primary bias string: R3 = (R1 R2)(+VS – 0.6V)/(additional hysteresis) Additional hysteresis is the desired overall hysteresis less the internal 4mV hysteresis. The second step is to recalculate R2 to set the same average threshold as before. The average threshold before was set at VTH = (VREF)(R1)/(R1 + R2). The new R2 is calculated based on the average output voltage (+VS/2) and the simplified circuit model in Figure 7. To assure that the comparator’s noninverting input is, on average, the same VTH as before: R2 ′ = (VREF – VTH)/(VTH/R1 + (VTH – VS/2)/R3) For additional hysteresis of 10mV or less, it is not uncom- mon for R2 ′ to be the same as R2 within 1% resistor tolerances. This method will work for additional hysteresis of up to a few hundred millivolts. Beyond that, the impedance of R3 is low enough to effect the bias string, and adjustment of R1 may also be required. Note that the currents through the R1/R2 bias string should be many times the input currents of the LT1715. For 5% accuracy, the current must be at least 20 times the input current, more for higher accuracy. Interfacing the LT1715 to ECL The LT1715’s comparators can be used in high speed applications where Emitter-Coupled Logic (ECL) is de- ployed. To interface the output of the LT1715 to ECL logic inputs, standard TTL/CMOS to ECL level translators such as the 10H124, 10H424 and 100124 can be used. These components come at a cost of a few nanoseconds addi- tional delay as well as supply currents of 50mA or more, and are only available in quads. A faster, simpler and lower power translator can be constructed with resistors as shown in Figure 8. Figure 8a shows the standard TTL to Positive ECL (PECL) resistive level translator. This translator cannot be used for the LT1715, or with CMOS logic, because it depends on the 820 Ωresistortolimittheoutputswing(VOH)oftheall-NPN TTL gate with its so-called totem-pole output. The LT1715 is fabricated in a complementary bipolar process and the output stage has a PNP driver that pulls the output nearly all the way to the supply rail, even when sourcing 10mA. Figure 8b shows a three resistor level translator for inter- facing the LT1715 to ECL running off the same supply rail. No pull-down on the output of the LT1715 is needed, but pull-down R3 limits the VIH seen by the PECL gate. This is needed because ECL inputs have both a minimum and maximum VIH specification for proper operation. Resistor values are given for both ECL interface types; in both cases it is assumed that the LT1715 operates from the same supply rail. Figure 8c shows the case of translating to PECL from an LT1715 powered by a 3V supply rail. Again, resistor values are given for both ECL interface types. This time four re- sistors are needed, although with 10KH/E, R3 is not needed. In that case, the circuit resembles the standard TTL trans- lator of Figure 8a, but the function of the new resistor, R4, is much different. R4 loads the LT1715 output when high so that the current flowing through R1 doesn’t forward bias the LT1715’s internal ESD clamp diode. Although this diode can handle 20mA without damage, normal Figure 7. Model for Additional Hysteresis Calculations Figure 6. Additional External Hysteresis – + 1/2 LT1715 INPUT 1715 F06 R2 VREF R3 R1 – + 1/2 LT1715 1715 F07 R2 ′ VREF VTH R3 +VS 2 VAVERAGE = R1 |
Similar Part No. - LT1715 |
|
Similar Description - LT1715 |
|
|
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 |
Family Site : ic2ic.com |
icmetro.com |