AD7616-PBSTZ datasheet(22/47 Pages) AD

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Data Sheet

AD7616-P

Rev. 0 | Page 21 of 46

THEORY OF OPERATION

CONVERTER DETAILS

The AD7616-P is a DAS that employs a high speed, low power,

charge redistribution, SAR ADC, and allows dual simultaneous

sampling of 16 analog input channels. The analog inputs on the

AD7616-P can accept true bipolar input signals. Analog input

range options include ±10 V, ±5 V, and ±2.5 V. The AD7616-P

operates from a single 5 V supply.

The AD7616-P contains input clamp protection, input signal

scaling amplifiers, a first-order antialiasing filter, an on-chip

reference, a reference buffer, a dual high speed ADC, a digital

filter, a flexible sequencer, and a high speed parallel interface.

The AD7616-P can be operated in hardware or software mode

by controlling the HW_RNGSELx pins. In hardware mode, the

AD7616-P is configured by pin control. In software mode, the

AD7616-P is configured by the control registers accessed via the

parallel interface.

ANALOG INPUT

Analog Input Channel Selection

The AD7616-P contains dual, simultaneous sampling, 16-bit

ADCs. Each ADC has eight analog input channels for a total of

16 analog input channels. Additionally, the AD7616-P has on-chip

diagnostic channels to monitor the VCC supply and an on-chip

adjustable LDO regulator. Channels can be selected for conversion

by using the CHSELx pins in hardware mode or via the channel

sample the diagnostic channels. Channels can be selected dynami-

cally or the AD7616-P has an on-chip sequencer to allow the

channels for conversion to be preprogrammed. In hardware mode,

simultaneous sampling is limited to the corresponding ADC A

and ADC B analog input channels. For example, Channel V0A

is always sampled with Channel V0B. In software mode, it is

possible to select any ADC A channel with any ADC B channel

for simultaneous sampling.

Analog Input Ranges

The AD7616-P can handle true bipolar, single-ended input

voltages. The logic levels on the range select pins, HW_RNGSEL0

and HW_RNGSEL1, determine the analog input range of all

analog input channels. If both range select pins are tied to a

logic low, the analog input range is determined in software mode

via the input range registers (see the Register Summary section

for more details). In software mode, it is possible to configure

an individual analog input range per channel.

Table 7. Analog Input Range Selection

Analog Input Range

HW_RNGSEL1

HW_RNGSEL0

Configured via the Input

Range Registers

±2.5 V

±5 V

±10 V

In hardware mode, a logic change on these pins has an immediate

effect on the analog input range; however, there is typically a

settling time of approximately 120 µs in addition to the normal

acquisition time requirement. The recommended practice is to

hardwire the range select pins according to the desired input

range for the system signals.

Analog Input Impedance

The analog input impedance of the AD7616-P is 1 MΩ, a fixed

input impedance that does not vary with the AD7616-P sampling

frequency. This high analog input impedance eliminates the need

for a driver amplifier in front of the AD7616-P, allowing direct

connection to the source or sensor.

Analog Input Clamp Protection

Figure 40 shows the analog input circuitry of the AD7616-P.

Each analog input of the AD7616-P contains clamp protection

circuitry. Despite single 5 V supply operation, this analog input

clamp protection allows an input overvoltage of between −20 V

and +20 V.

Figure 40. Analog Input Circuitry

Figure 41 shows the input clamp current vs. source voltage

characteristic of the clamp circuit. For source voltages between

−20 V and +20 V, no current flows in the clamp circuit. For input

voltages that are greater than +20 V and less than −20 V, the

AD7616-P clamp circuitry turns on.

Figure 41. Input Protection Clamp Profile, Input Clamp Current vs. Source Voltage

Place a series resistor on the analog input channels to limit the

current to ±10 mA for input voltages greater than +20 V and less

than −20 V. In an application where there is a series resistance

on an analog input, VxA or VxB, a corresponding resistance is

required on the analog input ground channel, VxAGND or

VxBGND (see Figure 42). If there is no corresponding resistor on

1MΩ

CLAMP

Vxx

1MΩ

CLAMP

VxxGND

FIRST-

ORDER

LPF

RFB

–0.25

–0.20

–0.15

–0.10

–0.05

0.05

0.10

0.15

0.20

0.25

–30

–20

–10

SOURCE VOLTAGE (V)

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