Electronic Components Datasheet Search |
|
AD546 Datasheet(PDF) 8 Page - Analog Devices |
|
AD546 Datasheet(HTML) 8 Page - Analog Devices |
8 / 12 page AD546 REV. A –8– Figure 28. Input Pin to Insulating Standoff Leakage through the bulk of the circuit board will still occur with the guarding schemes shown in Figures 27a and 27b. Stan- dard “G10” type printed circuit board material may not have high enough volume resistivity to hold leakages at the sub- picoampere level particularly under high humidity conditions. One option that eliminates all effects of board resistance is shown in Figure 28. The AD546’s sensitive input pin (either Pin 2 when connected as an inverter, or Pin 3 when connected as a follower) is bent up and soldered directly to a Teflon* insu- lated standoff. Both the signal input and feedback component leads must also be insulated from the circuit board by Teflon standoffs or low-leakage shielded cable. Contaminants such as solder flux on the board’s surface and on the amplifier’s package can greatly reduce the insulation resis- tance between the input pin and those traces with supply or sig- nal voltages. Both the package and the board must be kept clean and dry. An effective cleaning procedure is to first swab the sur- face with high grade isopropyl alcohol, then rinse it with deion- ized water and, finally, bake it at 80 °C for 1 hour. Note that if either polystyrene or polypropylene capacitors are used on the printed circuit board, a baking temperature of 70 °C is safer, since both of these plastic compounds begin to melt at approxi- mately +85 °C. Other guidelines include making the circuit layout as compact as possible and reducing the length of input lines. Keeping cir- cuit board components rigid and minimizing vibration will re- duce triboelectric and piezoelectric effects. All precision high impedance circuitry requires shielding from electrical noise and interference. For example, a ground plane should be used under all high value (i.e., greater than 1 M Ω) feedback resistors. In some cases, a shield placed over the resistors, or even the entire amplifier, may be needed to minimize electrical interference originating from other circuits. Referring to the equation in Fig- ure 26, this coupling can take place in either, or both, of two different forms—coupling via time varying fields: dV dT CP or by injection of parasitic currents by changes in capacitance due to mechanical vibration: dCp dT V Both proper shielding and rigid mechanical mounting of compo- nents help minimize error currents from both of these sources. Table I lists various insulators and their properties. Table I. Insulating Materials and Characteristics Volume Minimal Minimal Resistance Resistivity Triboelectric Piezoelectric to Water Material 1 ( –CM) Effects Effects Absorption Teflon* 10 17–1018 WW G Kel-F** 1017–1018 WM G Sapphire 10 16–1018 MG G Polyethylene 10 14–1018 MG M Polystyrene 1012–1018 WM M Ceramic 10 12–1014 WM W Glass Epoxy 10 10–1017 WM W PVC 1010–1015 GM G Phenolic 10 5–1012 WG W G–Good with Regard to Property. M–Moderate with Regard to Property. W–Weak with Regard to Property. 1Electronic Measurements, pp.15-17, Keithley Instruments, Inc., Cleveland, Ohio, 1977. *Teflon is a registered trademark of E.I. du Pont Co. **Kel-F is a registered trademark of 3M Company. OFFSET NULLING The AD546’s input offset voltage can be nulled by using balance Pins 1 and 5, as shown in Figure 29. Nulling the input offset voltage in this fashion will introduce an added input offset volt- age drift component of 2.4 µV/°C per millivolt of nulled offset. Figure 29. Standard Offset Null Circuit The circuit in Figure 30 can be used when the amplifier is used as an inverter. This method introduces a small voltage in series with the amplifier’s positive input terminal. The amplifier’s OBSOLETE |
Similar Part No. - AD546_15 |
|
Similar Description - AD546_15 |
|
|
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 |