Datasheet LTC1605-1, LTC1605-2 (Analog Devices) - 9

LTC1605-1/LTC1605-2
applicaTions inForMaTion
LT®1007 - Low noise precision amplifier. 2.7mA supply For minimum code transition noise the REF pin and the current ±5V to ±15V supplies. Gain bandwidth product CAP pin should each be decoupled with a capacitor to 8MHz. DC applications. filter wideband noise from the reference and the buffer LT1097 - Low cost, low power precision amplifier. 300µA (2.2µF tantalum). supply current. ±5V to ±15V supplies. Gain bandwidth
Offset and Gain Adjustments
product 0.7MHz. DC applications. The LTC1605-1/LTC1605-2 offset and full-scale er- LT1227 - 140MHz video current feedback amplifier. 10mA rors have been trimmed at the factory with the external supply current. ±5V to ±15V supplies. Low noise and low resistors shown in Figure 4. This allows for external distortion. adjustment of offset and full scale in applications where LT1360 - 37MHz voltage feedback amplifier. 3.8mA supply absolute accuracy is important. See Figure 5 for the off- current. ±5V to ±15V supplies. Good AC/DC specs. set and gain trim circuit for the LTC1605-1/LTC1605-2. LT1363 - 50MHz voltage feedback amplifier. 6.3mA supply First adjust the offset to zero by adjusting resistor R3. current. Good AC/DC specs. Apply an input voltage of 30.5µV (0.5LSB) and adjust R3 so the code is changing between 0000 0000 0000 0001 LT1364/LT1365 - Dual and quad 50MHz voltage feedback and 0000 0000 0000 0000. The gain error is trimmed by amplifiers. 6.3mA supply current per amplifier. Good AC/ adjusting resistor R4. An input voltage of 3.999908V (FS DC specs. – 1.5LSB) is applied to VIN and R4 is adjusted until the LT1468 - 90MHz, 22V/µs 16-Bit Accurate Amplifier output code is changing between 1111 1111 1111 1110 and 1111 1111 1111 1111. Figure 6a shows the unipolar transfer characteristic of the LTC1605-1. 200Ω AIN VIN For the LTC1605-2, first adjust the offset to zero by 1000pF 33.2k adjusting resistor R3. Apply an input voltage of –61µV CAP (–0.5LSB) and adjust R3 so the code is changing between 1605-1/2 F02 1111 1111 1111 1111 and 0000 0000 0000 0000. The gain
Figure 2. Analog Input Filtering
error is trimmed by adjusting resistor R4. An input voltage
Internal Voltage Reference
of 3.999817V (+FS – 1.5LSB) is applied to VIN and R4 is adjusted until the output code is changing between 0111 The LTC1605-1/LTC1605-2 has an on-chip, temperature 1111 1111 1110 and 0111 1111 1111 1111. Figure 6b compensated, curvature corrected, bandgap reference, shows the bipolar transfer characteristics of the LTC1605-2. which is factory trimmed to 2.50V. The full-scale range of the ADC is equal to (1.6VREF) or nominally 0V to 4V
DC Performance
for the LTC1605-1 and (±1.6VREF) or nominally ±4V for One way of measuring the transition noise associated with the LTC1605-2. The output of the reference is connected a high resolution ADC is to use a technique where a DC to the input of a unity-gain buffer through a 4k resistor signal is applied to the input of the ADC and the result- (see Figure 3). The input to the buffer or the output of the ing output codes are collected over a large number of reference is available at REF (Pin 3). The internal refer- conversions. For example, in Figure 7 the distribution of ence can be overdriven with an external reference if more output code is shown for a DC input that has been digitized accuracy is needed. The buffer output drives the internal 10000 times. The distribution is Gaussian and the RMS DAC and is available at CAP (Pin 4). The CAP pin can be code transition is about 1LSB. used to drive a steady DC load of less than 2mA. Driving an AC load is not recommended because it can cause the performance of the converter to degrade. 160512fa For more information www.linear.com/LTC1605-1 9