AD4693 datasheet(23/77 Pages) AD

23 / 77 page

Data Sheet

AD4693/AD4694

THEORY OF OPERATION

analog.com

Rev. 0 | 23 of 77

TRANSFER FUNCTION

Figure 48 shows the ideal transfer function of the AD4693/AD4694

SAR ADC core. The ADC core encodes the sampled voltage as

a fraction of the full-scale range (FSR) into a 16-bit digital code.

The transfer function consists of 216 LSBs, where 1 LSB is the

smallest discrete voltage step that can be resolved by the ADC

and is equal to (VREF/216)V. The AD4693/AD4694 input range is

unipolar (0 to VREF), and its output codes are in straight binary

format ranging from 0 to 65,535. Table 12 shows the ideal transfer

function mapping from input voltage to output code for each LSB

using VREF = 5V as an example.

Figure 48. ADC Ideal Transfer Function (FSR Is Full-Scale Range)

Table 12. ADC Input Voltage to Output Code Mapping

Description

Input Voltage

Digital Output Code

FSR − 1 LSB

(65535/65536) × VREF 0xFFFF

...

Midscale + 1 LSB

(32769/65536) × VREF 0x8001

Midscale

(½) × VREF

0x8000

Midscale − 1 LSB

(32767/65536) × VREF 0x7FFF

...

−FSR + 1 LSB

(1/65536) × VREF

0x0001

−FSR

0 V

0x0000

EASY DRIVE FEATURES

Traditional multiplexed SAR ADCs typically exhibit aggressive

charge and voltage transients on their analog inputs that require the

addition of high-speed, low-noise, and power-hungry ADC driver

amplifiers per channel. The need for dedicated ADC drivers per

channel drastically increases the system size and power dissipa-

tion, compromising the goal for small and power-efficient multichan-

nel precision measurements. The AD4693/AD4694 are equipped

with several Easy Drive features which ease the signal chain design

challenges associated with multiplexed SAR ADCs and enable

power- and space-efficient multichannel precision measurement

solutions.

The AD4693/AD4694 include analog input precharge buffers that

dramatically reduce the input transients typical of multiplexed SAR

ADCs. The smaller transients allow the AD4693/AD4694 to tolerate

higher impedance signal sources without compromised sampling

accuracy, thereby enabling direct interfacing with precision-focused

amplifiers without high-speed ADC drivers. The reduced transient

also allows for lower capacitance and higher resistance in the RC

input filters, reducing instability concerns and power dissipation for

the front-end amplifiers. See the Analog Input Precharge section for

more information.

The AD4693/AD4694 also include a precharge buffer on the REF

input to reduce transients on the VREF signal. The reference input

precharge buffer reduces the voltage reference transient response

requirements for directly driving the ADC REF input without a dedi-

cated reference buffer. The reduced average REF current reduces

also allows the ADC to tolerate larger series resistance between

the reference source and the REF input without compromising

accuracy.

The WLCSP package option for AD4693/AD4694 features a true

buffered reference input (REFIN). The internal reference buffer

is useful in applications using unbuffered, low power reference

sources, for references that require external noise filtering, or where

multiple devices share a common reference source. See the Inter-

nal Reference Buffer section for more information.

The AD4693/AD4694 include overvoltage protection clamps on

IN0 to IN7 and COM to reduce the risk of device damage from

sustained DC overvoltage events. These clamps eliminate the need

for external clamping diodes in systems where the input driving

circuitry positive supply rail is greater than VREF. See the Input

Overvoltage Protection Clamps section for more information.

AD4693 Datasheet(PDF) 23 Page - Analog Devices

AD4693 Datasheet(HTML) 23 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77

Datasheet Download

Link URL