Datasheet LTC6362 (Analog Devices) - 10

LTC6362
APPLICATIONS INFORMATION Functional Description General Amplifier Applications
The LTC6362 is a low power, low noise, high DC accuracy In Figure 1, the gain to VOUTDIFF from VINP and VINM is fully differential operational amplifier/ADC driver. The given by: amplifier is optimized to convert a fully differential or single-ended signal to a low impedance, balanced differ-  R  V F ( ) ential output suitable for driving high performance, low OUTDIFF = V+OUT − V–OUT ≈  RI  • VINP – VINM power differential successive approximation register (SAR) ADCs. The balanced differential nature of the amplifier Note from the previous equation, the differential output also provides even-order harmonic distortion cancella- voltage (V+OUT – V–OUT) is completely independent of tion, and low susceptibility to common mode noise (like input and output common mode voltages, or the voltage power supply noise). at the common mode pin. This makes the LTC6362 ideally suited for pre-amplification, level shifting and conversion The outputs of the LTC6362 are capable of swinging rail- of single-ended signals to differential output signals for to-rail and can source or sink up to 35mA of current. The driving differential input ADCs. LTC6362 is optimized for high bandwidth and low power applications. Load capacitances above 10pF to ground or
Output Common Mode and VOCM Pin
5pF differentially should be decoupled with 10Ω to 100Ω of series resistance from each output to prevent oscilla- The output common mode voltage is defined as the aver- tion or ringing. Feedback should be taken directly from age of the two outputs: the amplifier output. Higher voltage gain configurations  V+OUT + V–OUT  tend to have better capacitive drive capability than lower VOUTCM = VOCM =  2  gain configurations due to lower closed-loop bandwidth. As the equation shows, the output common mode voltage
Input Pin Protection
is independent of the input common mode voltage, and The LTC6362 input stage is protected against differential is instead determined by the voltage on the VOCM pin, by input voltages which exceed 1.4V by two pairs of series means of an internal common mode feedback loop. diodes connected back-to-back between +IN and –IN. If the V Moreover, all pins have clamping diodes to both power OCM pin is left open, an internal resistor divider develops a default voltage of 2.5V with a 5V supply. The supplies. If any pin is driven to voltages which exceed V either supply, the current should be limited to under 10mA OCM pin can be overdriven to another voltage if desired. For example, when driving an ADC, if the ADC makes a to prevent damage to the IC. reference available for setting the common mode volt-
SHDN Pin
age, it can be directly tied to the VOCM pin, as long as the ADC is capable of driving the 170k input resistance The LTC6362 has a SHDN pin which when driven to within presented by the VOCM pin. The Electrical Characteristics 0.8V above the negative rail, will shut down amplifier op- table specifies the valid range that can be applied to the eration such that only 70µA is drawn from the supplies. VOCM pin (VOUTCMR). Pull-down circuitry should be capable of sinking at least 4µA to guarantee complete shutdown across all condi- tions. For normal operation, the SHDN pin should be left floating or tied to the positive rail. 6362fa 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Package Description Revision History Typical Application Related Parts