Datasheet AD7606, AD7606-6, AD7606-4 (Analog Devices) - 22

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AD7606/AD7606-6/AD7606-4 Data Sheet THEORY OF OPERATION CONVERTER DETAILS Analog Input Clamp Protection
The AD7606/AD7606-6/AD7606-4 are data acquisition systems Figure 34 shows the analog input structure of the AD7606/ that employ a high speed, low power, charge redistribution, AD7606-6/AD7606-4. Each analog input of the AD7606/ successive approximation analog-to-digital converter (ADC) AD7606-6/AD7606-4 contains clamp protection circuitry. and allow the simultaneous sampling of eight/six/four analog input Despite single 5 V supply operation, this analog input clamp channels. The analog inputs on the AD7606/AD7606-6/AD7606-4 protection al ows for an input over voltage of up to ±16.5 V. can accept true bipolar input signals. The RANGE pin is used to
RFB
select either ±10 V or ±5 V as the input range. The AD7606/
1MΩ
AD7606-6/AD7606-4 operate from a single 5 V supply.
Vx CLAMP 1MΩ
The AD7606/AD7606-6/AD7606-4 contain input clamp
VxGND CLAMP SECOND-
protection, input signal scaling amplifiers, a second-order anti-
ORDER
032
R LPF FB
aliasing filter, track-and-hold amplifiers, an on-chip reference, 08479- Figure 34. Analog Input Circuitry reference buffers, a high speed ADC, a digital filter, and high speed parallel and serial interfaces. Sampling on the AD7606/ Figure 35 shows the voltage vs. current characteristic of the AD7606-6/AD7606-4 is controlled using the CONVST signals. clamp circuit. For input voltages of up to ±16.5 V, no current flows in the clamp circuit. For input voltages that are above ±16.5 V,
ANALOG INPUT
the AD7606/AD7606-6/AD7606-4 clamp circuitry turns on.
Analog Input Ranges AV 30 CC, VDRIVE = 5V
The AD7606/AD7606-6/AD7606-4 can handle true bipolar,
TA = 25°C
single-ended input voltages. The logic level on the RANGE pin
20
determines the analog input range of all analog input channels.
mA) ( 10
If this pin is tied to a logic high, the analog input range is ±10 V
NT
for all channels. If this pin is tied to a logic low, the analog input
0
range is ±5 V for al channels. A logic change on this pin has an
CURRE P –10
immediate effect on the analog input range; however, there is
AM –20
typical y a settling time of approximately 80 µs, in addition to
CL UT
the normal acquisition time requirement. The recommended
–30 INP
practice is to hardwire the RANGE pin according to the desired
–40
input range for the system signals.
–50
During normal operation, the applied analog input voltage
–20 –15 –10 –5 0 5 10 15 20
033
SOURCE VOLTAGE (V)
should remain within the analog input range selected via the 08479- Figure 35. Input Protection Clamp Profile RANGE pin. A RESET pulse must be applied after power up to ensure the analog input channels are configured for the range A series resistor should be placed on the analog input channels selected. to limit the current to ±10 mA for input voltages above ±16.5 V. When in a power-down mode, it is recommended to tie the In an application where there is a series resistance on an analog analog inputs to GND. Per the Analog Input Clamp Protection input channel, Vx, a corresponding resistance is required on the section, the overvoltage clamp protection is recommended for analog input GND channel, VxGND (see Figure 36). If there is use in transient overvoltage conditions and should not remain no corresponding resistor on the VxGND channel, an offset active for extended periods. Stressing the analog inputs outside error occurs on that channel. It is recommended that the input of the conditions mentioned here may degrade the bipolar zero overvoltage clamp protection circuitry be used to protect the AD7606/AD7606-6/AD7606-4 against transient overvoltage code error and THD performance of the AD7606/AD7606-6/ events. It is not recommended to leave the AD7606/AD7606-6/ AD7606-4. AD7606-4 in a condition where the clamp protection circuitry
Analog Input Impedance
is active in normal or power-down conditions for extended The analog input impedance of the AD7606/AD7606-6/ periods because this may degrade the bipolar zero code error AD7606-4 is 1 MΩ. This is a fixed input impedance that does performance of the AD7606/AD7606-6/AD7606-4. not vary with the AD7606 sampling frequency. This high analog input impedance eliminates the need for a driver amplifier in front of the AD7606/AD7606-6/AD7606-4, allowing for direct connection to the source or sensor. With the need for a driver amplifier eliminated, bipolar supplies (which are often a source of noise in a system) can be removed from the signal chain. Rev. C | Page 22 of 36 Document Outline Features Applications Functional Block Diagram Revision History General Description Specifications Timing Specifications Timing Diagrams Absolute Maximum Ratings Thermal Resistance ESD Caution Pin Configurations and Function Descriptions Typical Performance Characteristics Terminology Theory of Operation Converter Details Analog Input Analog Input Ranges Analog Input Impedance Analog Input Clamp Protection Analog Input Antialiasing Filter Track-and-Hold Amplifiers ADC Transfer Function Internal/External Reference Typical Connection Diagram Power-Down Modes Conversion Control Simultaneous Sampling on All Analog Input Channels Simultaneously Sampling Two Sets of Channels Digital Interface Parallel Interface (PAR/SER/BYTE SEL = 0) Parallel Byte (PAR/SER/BYTE SEL = 1, DB15 = 1) Serial Interface (PAR/SER/BYTE SEL = 1) Reading During Conversion Digital Filter Layout Guidelines Outline Dimensions Ordering Guide