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LT1220 Datasheet(PDF) 7 Page - Linear Technology |
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LT1220 Datasheet(HTML) 7 Page - Linear Technology |
7 / 12 page 7 LT1220 APPLICATIONS INFORMATION Input Considerations Bias current cancellation circuitry is employed on the inputs of the LT1220 so the input bias current and input offset current have identical specifications. For this reason, matching the impedance on the inputs to reduce bias current errors is not necessary. Capacitive Loading The LT1220 is stable with capacitive loads. This is accom- plished by sensing the load induced output pole and adding compensation at the amplifier gain node. As the capacitive load increases, both the bandwidth and phase margin decrease. There will be peaking in the frequency domain as shown in the curve of Frequency Response vs Capacitive Load. The small-signal transient response will have more overshoot as shown in the photo of the small-signal response with 1000pF load. The large-signal response with a 10,000pF load shows the output slew rate being limited to 4V/ µs by the short-circuit current. The LT1220 can drive coaxial cable directly, but for best pulse fidelity a resistor of value equal to the characteristic impedance of the cable (i.e., 75 Ω) should be placed in series with the output. The other end of the cable should be terminated with the same value resistor to ground. DAC Current-to-Voltage Amplifier The high gain, low offset voltage, low input bias current, and fast settling of the LT1220 make it particularly useful as an I/V converter for current output DACs. A typical application is shown with a 565A type, 12-bit, 2mA full- scale output current DAC. The 5k resistor around the LT1220 is internal to the DAC and gives a 10V full-scale output voltage. A 5pF capacitor in parallel with the feedback resistor compensates for the DAC output capacitance and improves settling. The output of the LT1220 settles to 1/2LSB (1.2mV) in less than 300ns. The accuracy of this circuit is equal to: VERROR = VOS + (IOS • 5kΩ) + (VOUT/AVOL) At room temperature the worst-case error is 3mV (1.2LSB). Typically the error is 1.2mV (1/2LSB). Over the commercial temperature range the worse-case error is 6mV (2.5LSB). 6 OUT LT1220 • SS BIAS 2 BIAS 1 18 NULL –IN +IN 3 V – 7 V+ 2 4 SI PLIFIED SCHE ATIC |
Similar Part No. - LT1220_01 |
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Similar Description - LT1220_01 |
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