Datasheet LT1259, LT1260 (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | Low Cost Dual and Triple 130MHz Current Feedback Amplifiers with Shutdown |
| Pages / Page | 12 / 7 — SI PLIFIED SCHE ATIC , each amplifier. APPLICATIO S I FOR ATIO. Feedback … |
| File Format / Size | PDF / 337 Kb |
| Document Language | English |
SI PLIFIED SCHE ATIC , each amplifier. APPLICATIO S I FOR ATIO. Feedback Resistor Selection. Power Supplies
Model Line for this Datasheet
Text Version of Document
LT1259/LT1260
W W SI PLIFIED SCHE ATIC , each amplifier
V+ +IN –IN OUT EN V– LT1259/60 • SS
U U W U APPLICATIO S I FOR ATIO Feedback Resistor Selection
more stable at higher gains. Alternatively, a small resistor (10Ω to 20Ω) can be put in series with the output to isolate The small-signal bandwidth of the LT1259/ LT1260 are set the capacitive load from the amplifier output. This has the by the external feedback resistors and the internal junction advantage that the amplifier bandwidth is only reduced capacitors. As a result, the bandwidth is a function of the when the capacitive load is present. The disadvantage is supply voltage, the value of the feedback resistor, the that the gain is a function of the load resistance. closed-loop gain and the load resistor. The LT1259/LT1260 have been optimized for ±5V supply operation and have a
Power Supplies
– 3dB bandwidth of 90MHz. See resistor selection guide in Typical AC Performance table. The LT1259/LT1260 will operate from single or split supplies from ±2V (4V total) to ±15V (30V total). It is not
Capacitance on the Inverting Input
necessary to use equal value split supplies, however the offset voltage and inverting input bias current will change. Current feedback amplifiers require resistive feedback The offset voltage changes about 500µV per volt of from the output to the inverting input for stable operation. supply mismatch. The inverting bias current can change Take care to minimize the stray capacitance between the as much as 5µA per volt of supply mismatch though output and the inverting input. Capacitance on the invert- typically, the change is about 0.1µA per volt. ing input to ground will cause peaking in the frequency response (and overshoot in the transient response). See
Slew Rate
the section on Demo Board Information. The slew rate of a current feedback amplifier is not
Capacitive Loads
independent of the amplifier gain configuration the way slew rate is in a traditional op amp. This is because both the The LT1259/LT1260 can drive capacitive loads directly input stage and the output stage have slew rate limitations. when the proper value of feedback resistor is used. The In the inverting mode, and for higher gains in the nonin- graph of Maximum Capacitive Load vs Feedback Resistor verting mode, the signal amplitude between the input pins should be used to select the appropriate value. The value is small and the overall slew rate is that of the output stage. shown is for ≤ 5dB peaking when driving a 150Ω load at a For gains less than ten in the noninverting mode, the gain of 2. This is a worst case condition. The amplifier is overall slew rate is limited by the input stage. 7
W W SI PLIFIED SCHE ATIC , each amplifier
V+ +IN –IN OUT EN V– LT1259/60 • SS
U U W U APPLICATIO S I FOR ATIO Feedback Resistor Selection
more stable at higher gains. Alternatively, a small resistor (10Ω to 20Ω) can be put in series with the output to isolate The small-signal bandwidth of the LT1259/ LT1260 are set the capacitive load from the amplifier output. This has the by the external feedback resistors and the internal junction advantage that the amplifier bandwidth is only reduced capacitors. As a result, the bandwidth is a function of the when the capacitive load is present. The disadvantage is supply voltage, the value of the feedback resistor, the that the gain is a function of the load resistance. closed-loop gain and the load resistor. The LT1259/LT1260 have been optimized for ±5V supply operation and have a
Power Supplies
– 3dB bandwidth of 90MHz. See resistor selection guide in Typical AC Performance table. The LT1259/LT1260 will operate from single or split supplies from ±2V (4V total) to ±15V (30V total). It is not
Capacitance on the Inverting Input
necessary to use equal value split supplies, however the offset voltage and inverting input bias current will change. Current feedback amplifiers require resistive feedback The offset voltage changes about 500µV per volt of from the output to the inverting input for stable operation. supply mismatch. The inverting bias current can change Take care to minimize the stray capacitance between the as much as 5µA per volt of supply mismatch though output and the inverting input. Capacitance on the invert- typically, the change is about 0.1µA per volt. ing input to ground will cause peaking in the frequency response (and overshoot in the transient response). See
Slew Rate
the section on Demo Board Information. The slew rate of a current feedback amplifier is not
Capacitive Loads
independent of the amplifier gain configuration the way slew rate is in a traditional op amp. This is because both the The LT1259/LT1260 can drive capacitive loads directly input stage and the output stage have slew rate limitations. when the proper value of feedback resistor is used. The In the inverting mode, and for higher gains in the nonin- graph of Maximum Capacitive Load vs Feedback Resistor verting mode, the signal amplitude between the input pins should be used to select the appropriate value. The value is small and the overall slew rate is that of the output stage. shown is for ≤ 5dB peaking when driving a 150Ω load at a For gains less than ten in the noninverting mode, the gain of 2. This is a worst case condition. The amplifier is overall slew rate is limited by the input stage. 7
