Datasheet AD215 (Analog Devices) - 8

AD215 POWERING THE AD215 Noninverting Configuration for Gain Greater Than Unity
The AD215 is powered by a bipolar ± 15 V dc power supply Figure 13 shows how to achieve a gain greater than one while connected as shown in Figure 11. External bypass capacitors continuing to preserve a very high input impedance. A recom- should be provided in bused applications. Note that a small mended PC board layout for multichannel applications is shown signal-related current (50 mA/VOUT) will flow out of the OUT in Figure 20b. LO pin (Pin 37). Therefore, the OUT LO terminals should be bused together and referenced at a single “Analog Star Ground”
R
to the ± 15 V dc supply common as illustrated Figure 11.
IN = 2k
Ω
IN+ 1 OUT HI IN– OUTPUT 38 3 FILTER, C AD215 F N AD2151 V RF BUFFER ANALOG STAR GROUND SIGNAL 47pF FB AND 4 R OUT LO G TRIM N OUT LO1 IN COM OUT LO 37 37 SIG COM 2 CIRCUITRY 37 TRIM +V 36 IN 42 42 +15V dc AD215 COM 43 2.2µF PWR PWR RTN RTN 43 43 COM 2.2µF –VIN 44 44 –15V dc
Figure 13. Noninverting Input Configuration for Gain > 1 V/V
NTH CHANNEL 1ST CHANNEL
In this circuit, the gain equation is as follows: V Figure 11. Typical Power Supply Connections O = (1 + RF/RG) × VSIG where:
Power Supply Voltage Considerations
The rated performance of the AD215 remains unaffected for VO = Output Voltage (V) power supply voltages in the ± 14.5 V dc to ± 16.5 V dc range. VSIG = Input Signal Voltage (V) Voltages below ± 14.25 V dc may cause the AD215 to cease op- RF = Feedback Resistor Value (Ω) erating properly. RG = Gain Resistor Value (Ω) Note: Power supply voltages greater than ±17.5 V dc may damage The values for resistors RF and RG are subject to the following the internal components and consequently should not be used. constraints: • The total impedance of the gain network should be less than
USING THE AD215
10 kΩ.
Unity Gain Input Configuration
The basic unity gain configuration for input signals of up to • The current drawn in RF is less than 1 mA at ± 10 V. Note that ±10 V is shown in Figure 12. for each mA drawn by the feedback resistor, the isolated power supply drive capability decreases by 1 mA.
R
• Amplifier gain is set by the feedback (R
IN = 2k
Ω F) and gain resistor
IN+ 1 OUT HI
(RG).
IN– 38 3 OUTPUT FILTER, VSIGNAL FB BUFFER AND
It is recommended that RF is bypassed with a 47 pF capacitor as
4 TRIM CIRCUITRY IN COM OUT LO
shown.
2 37 TRIM
Note: The 2 kΩ input resistor (R
36
IN) in series with the input
AD215 COM
signal source and the IN+ terminal in Figures 12 and 13 is rec-
43 PWR
ommended to limit the current at the input terminals of the to
RTN
5.0 mA when the AD215 is not powered. Figure 12. Basic Unity Gain REV. 0 –7–