Datasheet LTC1606 (Analog Devices) - 9

LTC1606
U U W U APPLICATIO S I FOR ATIO
capacitor as close to the device input pin as possible. If an 4k REF 3 BANDGAP amplifier is to be used to drive the input, care should be (2.5V) REFERENCE taken to select an amplifier with adequate accuracy, linear- 2.2µF + – ity and noise for the application. The following list is a R summary of the op amps that are suitable for driving the 0.64R LTC1606. More detailed information is available in the CAP 4 Linear Technology data books and LinearViewTM CD-ROM. (4.096V) INTERNAL LT1007: Low noise precision amplifier. 2.7mA supply 10µF CAPACITOR DAC current ±5V to ±15V supplies. Gain bandwidth product 8MHz. DC applications. 1606 • F03 LT1097: Low cost, low power precision amplifier. 300µA supply current. ±5V to ±15V supplies. Gain bandwidth
Figure 3. Internal or External Reference Source
product 0.7MHz. DC applications. LT1227: 140MHz video current feedback amplifier. 10mA For minimum code transition noise, the REF pin and the supply current. ±5V to ±15V supplies. Low noise and low CAP pin should each be decoupled with a capacitor to distortion. filter wideband noise from the reference and the buffer (2.2µF tantalum for the REF pin and 10µF tantalum for the LT1360: 37MHz voltage feedback amplifier. 3.8mA supply CAP pin). To prevent the 10µF bypass capacitor from current. ±5V to ±15V supplies. Good AC/DC specs. discharging through the CAP pin if the positive supply LT1363: 50MHz voltage feedback amplifier. 6.3mA supply (VDIG and VANA) were to drop, a diode (1N4148 or current. Good AC/DC specs. equivalent) can be placed between the CAP pin and the positive supply. LT1364/LT1365: Dual and quad 50MHz voltage feedback amplifiers. 6.3mA supply current per amplifier. Good AC/
Offset and Gain Adjustments
DC specs. The LTC1606 offset and full-scale errors have been trimmed LT1468: 90MHz 22V/µs 16-bit accurate amplifier. at the factory with the external resistors shown in Figure LT1469: Dual LT1468 4. This allows for external adjustment of offset and full scale in applications where absolute accuracy is impor-
Internal Voltage Reference
tant. See Figure 5 for the offset and gain trim circuit. The 100k resistor in parallel with the 33.2k is only needed for The LTC1606 has an on-chip, temperature compensated, externally trimming the offset. First, adjust the offset to curvature corrected, bandgap reference, which is factory zero by adjusting resistor R3. Apply an input voltage trimmed to 2.50V. The full-scale range of the ADC is equal of –152.6µV (– 0.5LSB) and adjust R3 so the code is to (±4 • VREF) or nominally ±10V. The output of the reference is connected to the input of a buffer (1.64x) 1 through a 4k resistor (see Figure 3). The input to the buffer ±10V INPUT VIN 2 200Ω or the output of the reference is available at REF (Pin 3). AGND1 1% The internal reference can be overdriven with an external + 2.2µF LTC1606 33.2k 3 reference if more accuracy is needed. The buffer output 1% REF 4 4.096V CAP drives the internal DAC and is available at CAP (Pin 4). The + 10µF CAP pin can be used to drive a steady DC load of less than 5 AGND2 2mA. Driving an AC load is not recommended because it 1606 • F04 can cause the performance of the converter to degrade.
Figure 4.
±
10V Input Without Trim
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