 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LMC660AIN Datasheet(PDF) 8 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LMC660AIN Datasheet(HTML) 8 Page - National Semiconductor (TI) |
|
|
8 / 14 page  Application Hints (Continued) Capacitive load driving capability is enhanced by using a pull up resistor to V + (Figure 4). Typically a pull up resistor con- ducting 500 µA or more will significantly improve capacitive load responses. The value of the pull up resistor must be de- termined based on the current sinking capability of the ampli- fier with respect to the desired output swing. Open loop gain of the amplifier can also be affected by the pull up resistor (see Electrical Characteristics). PRINTED-CIRCUIT-BOARD LAYOUT FOR HIGH-IMPEDANCE WORK It is generally recognized that any circuit which must operate with less than 1000 pA of leakage current requires special layout of the PC board. When one wishes to take advantage of the ultra-low bias current of the LMC662, typically less than 0.04 pA, it is essential to have an excellent layout. For- tunately, the techniques for obtaining low leakages are quite simple. First, the user must not ignore the surface leakage of the PC board, even though it may sometimes appear accept- ably low, because under conditions of high humidity or dust or contamination, the surface leakage will be appreciable. To minimize the effect of any surface leakage, lay out a ring of foil completely surrounding the LMC660’s inputs and the terminals of capacitors, diodes, conductors, resistors, relay terminals, etc. connected to the op-amp’s inputs. See Figure 5. To have a significant effect, guard rings should be placed on both the top and bottom of the PC board. This PC foil must then be connected to a voltage which is at the same voltage as the amplifier inputs, since no leakage current can flow between two points at the same potential. For example, a PC board trace-to-pad resistance of 10 12 Ω, which is nor- mally considered a very large resistance, could leak 5 pA if the trace were a 5V bus adjacent to the pad of an input. This would cause a 100 times degradation from the LMC660’s ac- tual performance. However, if a guard ring is held within 5 mV of the inputs, then even a resistance of 10 11 Ω would cause only 0.05 pA of leakage current, or perhaps a minor (2:1) degradation of the amplifier’s performance. See Figure 6a, Figure 6b, Figure 6c for typical connections of guard rings for standard op-amp configurations. If both inputs are active and at high impedance, the guard can be tied to ground and still provide some protection; see Figure 6d. DS008767-5 FIGURE 3. Rx, Cx Improve Capacitive Load Tolerance DS008767-23 FIGURE 4. Compensating for Large Capacitive Loads with a Pull Up Resistor DS008767-16 FIGURE 5. Example, using the LMC660, of Guard Ring in P.C. Board Layout www.national.com 8 |
Similar Part No. - LMC660AIN |
|
Similar Description - LMC660AIN |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | 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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
