Datasheet LTC1605 (Analog Devices) - 9

LTC1605
APPLICATIONS INFORMATION Conversion Details
the end of a conversion, the DAC output balances the VIN The LTC1605 uses a successive approximation algo- input charge. The SAR contents (a 16-bit data word) that rithm and an internal sample-and-hold circuit to convert represents the VIN are loaded into the 16-bit output latches. an analog signal to a 16-bit or two byte parallel output.
Driving the Analog Inputs
The ADC is complete with a precision reference and an internal clock. The control logic provides easy interface The nominal input range for the LTC1605 is ±10V to microprocessors and DSPs. (Please refer to the Digital or (±4 • VREF) and the input is overvoltage protected to Interface section for the data format.) ±25V. The input impedance is typically 20kΩ, therefore, it should be driven with a low impedance source. Wideband Conversion start is controlled by the CS and R/C inputs. noise coupling into the input can be minimized by placing At the start of conversion the successive approximation a 1000pF capacitor at the input as shown in Figure 2. An register (SAR) is reset. Once a conversion cycle has begun NPO-type capacitor gives the lowest distortion. Place the it cannot be restarted. capacitor as close to the device input pin as possible. If During the conversion, the internal 16-bit capacitive DAC an amplifier is to be used to drive the input, care should output is sequenced by the SAR from the most significant be taken to select an amplifier with adequate accuracy, bit (MSB) to the least significant bit (LSB). Referring to linearity and noise for the application. The following list Figure 1, VIN is connected through the resistor divider to the is a summary of the op amps that are suitable for driving sample-and-hold capacitor during the acquire phase and the LTC1605. More detailed information is available at the comparator offset is nulled by the autozero switches. www.linear.com. In this acquire phase, a minimum delay of 2µs will provide enough time for the sample-and-hold capacitor to acquire 200Ω AIN VIN the analog signal. During the convert phase, the autozero 1000pF 33.2k switches open, putting the comparator into the compare CAP mode. The input switch switches CSAMPLE to ground, 1605 • F02 injecting the analog input charge onto the summing junc-
Figure 2. Analog Input Filtering
tion. This input charge is successively compared with the binary-weighted charges supplied by the capacitive DAC.
LT®1007:
Low noise precision amplifier. 2.7mA supply Bit decisions are made by the high speed comparator. At current ±5V to ±15V supplies. Gain bandwidth product 8MHz. DC applications. SAMPLE
LT1097:
Low cost, low power precision amplifier. 300µA C SI supply current. ±5V to ±15V supplies. Gain bandwidth RIN1 SAMPLE SAMPLE V product 0.7MHz. DC applications. IN – HOLD R
LT1227:
140MHz video current feedback amplifier. 10mA IN2 + C supply current. ±5V to ±15V supplies. Low noise and low DAC COMPARATOR DAC distortion. VDAC S A
LT1360:
37MHz voltage feedback amplifier. 3.8mA supply R current. ±5V to ±15V supplies. Good AC/DC specs. 16-BIT
LT1363:
50MHz voltage feedback amplifier. 6.3mA supply LATCH current. Good AC/DC specs. 1605 • F01
Figure 1. LTC1605 Simplified Equivalent Circuit LT1364/LT1365:
Dual and quad 50MHz voltage feedback amplifiers. 6.3mA supply current per amplifier. Good AC/ DC specs. 1605fd For more information www.linear.com/LTC1605 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Converter Characteristics Analog Input Dynamic Accuracy Internal Reference Characteristics Digital Inputs and Outputs Timing Characteristics Power Requirements Typical Performance Characteristics Pin Functions Test Circuit Functional Block Diagram Applications Information Package Description Revision History Package Description Related Parts