Datasheet LTC1402 (Analog Devices) - 11

LTC1402
U U W U APPLICATIONS INFORMATION
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LT1630:
Dual 30MHz Rail-to-Rail Voltage FB Amplifier. Ω ANALOG 3 A + IN INPUT 2.7V to ±15V supplies. Very high AVOL, 500µV offset and 68pF 4 520ns settling to 0.5LSB for a 4V swing. THD and noise A – IN are – 93dB to 40kHz and below 1LSB to 320kHz (AV = 1, 2 AGND1 2VP-P into 1kΩ, VS = 5V), making the part excellent for AC LTC1402 5 applications (to 1/3 Nyquist) where rail-to-rail perfor- VREF 10µF mance is desired. Quad version is available as LT1631. 6 AGND2
LT1632:
Dual 45MHz Rail-to-Rail Voltage FB Amplifier. 7 GAIN 2.7V to ±15V supplies. Very high AVOL, 1.5mV offset and 1402 F02 400ns settling to 0.5LSB for a 4V swing. It is suitable for applications with a single 5V supply. THD and noise are
Figure 2. RC Input Filter
– 93dB to 40kHz and below 1LSB to 800kHz (AV = 1, 2VP-P into 1kΩ, VS = 5V), making the part excellent for AC less susceptible to both problems. When high amplitude applications where rail-to-rail performance is desired. unwanted signals are close in frequency to the desired signal Quad version is available as LT1633. frequency, a multiple pole filter is required. Figure 3 shows
LT1813:
Dual 100MHz 750V/µs 3mA Voltage Feedback a simple implementation using an LTC1560-1, a fifth␣ order Amplifier. 5V to ±5V supplies. Distortion is – 86dB to elliptic continuous-time 1MHz filter. 100kHz and – 77dB to 1MHz with ±5V supplies (2VP-P into 500Ω). Excellent part for fast AC applications with 1 8 3 A + IN ±5V␣ supplies. 2 7 4 V – IN AIN LTC1560-1 3 6 2
INPUT FILTERING AND SOURCE IMPEDANCE
AGND1 LTC1402 The noise and the distortion of the input amplifier and 4 5 5 –5V 5V VREF other circuitry must be considered since they will add to 10µF 0.1µF 0.1µF 6 AGND2 the LTC1402 noise and distortion. The small-signal band- width of the sample-and-hold circuit is 80MHz. Any noise 7 GAIN or distortion products that are present at the analog inputs 1402 F03 will be summed over this entire bandwidth. Noisy input
Figure 3. 1MHz Fifth Order Elliptic Lowpass Filter
circuitry should be filtered prior to the analog inputs to minimize noise. A simple 1-pole RC filter is sufficient for many applications. For example, Figure 2 shows a 68pF
BIPOLAR AND UNIPOLAR INPUT RANGES
capacitor from A + IN to ground and a 51Ω source resistor The ±2V bipolar input range of the LTC1402 is optimized to limit the input bandwidth to 47MHz. The 68pF capacitor for low noise and low distortion. Most op amps also also acts as a charge reservoir for the input sample-and- perform best over this same range, allowing direct cou- hold and isolates the ADC input from sampling glitch- pling to the analog inputs and eliminating the need for sensitive circuitry. special translation circuitry. The inputs of the LTC1402 High quality capacitors and resistors should be used since may also be driven fully differential in bipolar mode with these components can add distortion. NPO and silver mica a single supply. Each input should not swing more than type dielectric capacitors have excellent linearity. 2VP-P individually to get the best performance from single supply amplifiers. Carbon surface mount resistors can generate distortion from self heating and from damage that may occur during The 0V to 4V range is ideal for single ended input use with soldering. Metal film surface mount resistors are much single supply applications. 11