AD7653AST Analog Devices Inc, AD7653AST Datasheet - Page 15

• Manufacturer Part Number: AD7653AST
• Description: IC ADC 16BIT 1MSPS W/REF 48-LQFP
• Manufacturer: Analog Devices Inc
• Series: PulSAR®r

Specifications of AD7653AST

• Rohs Status: RoHS non-compliant
• Number Of Bits: 16
• Sampling Rate (per Second): 1M
• Data Interface: Serial, Parallel
• Number Of Converters: 1
• Power Dissipation (max): 145mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• For Use With: EVAL-AD7653CBZ - BOARD EVALUATION FOR AD7653

CIRCUIT INFORMATION
The AD7653 is a very fast, low power, single supply, precise
16-bit analog-to-digital converter (ADC). The AD7653 features
different modes to optimize performance according to the
application. In Warp mode, the part can convert 1 million
samples per second.
The AD7653 provides the user with an on-chip track/hold,
successive approximation ADC that does not exhibit any
pipeline or latency, making it ideal for multiple multiplexed
channel applications.
The AD7653 can be operated from a single 5 V supply and can
be interfaced to either 5 V or 3 V digital logic. It is housed in
either a 48-lead LQFP or a 48-lead LFCSP that saves space and
allows flexible configurations as either a serial or a parallel
interface. The AD7653 is a pin-to-pin compatible upgrade of the
AD7651/AD7652.
CONVERTER OPERATION
The AD7653 is a successive approximation ADC based on a
charge redistribution DAC. F
schematic of the ADC. The capacitive DAC consists of an array
of 16 binary weighted capacitors and an additional LSB
capacitor. The comparator’s negative input is connected to a
dummy capacitor of the same value as the capacitive DAC array.
During the acquisition phase, the common terminal of the array
tied to the comparator’s positive input is connected to AGND
via SWA. All independent switches are connected to the analog
input IN. Thus, the capacitor array is used as a sampling
capacitor and acquires the analog signal on IN. Similarly, the
dummy capacitor acquires the analog signal on INGND.
When CNVST goes LOW, a conversion phase is initiated. When
the conversion phase begins, SWA and SWB are opened. The
capacitor array and dummy capacitor are then disconnected
REFGND
INGND
REF
IN
igure 20
32,768C
shows a simplified
16,384C
MSB
4C
Figure 20. ADC Simplified Schematic
Rev. A | Page 15 of 28
2C
65,536C
C
from the inputs and connected to REFGND. Therefore, the
differential voltage between IN and INGND captured at the end
of the acquisition phase is applied to the comparator inputs,
causing the comparator to become unbalanced. By switching
each element of the capacitor array between REFGND and REF,
the comparator input varies by binary weighted voltage steps
(VREF/2, VREF/4, …VREF/65536). The control logic toggles
these switches, starting with the MSB, to bring the comparator
back into a balanced condition.
After this process is completed, the control logic generates the
ADC output code and brings the BUSY output LOW.
Modes of Operation
The AD7653 features three modes of operations: Warp, Normal,
and Impulse. Each mode is best suited for specific applications.
Warp mode allows the fastest conversion rate up to 1 MSPS.
However in this mode and this mode only, the full specified
accuracy is guaranteed only when the time between conversions
does not exceed 1 ms. If the time between two consecutive
conversions is longer than 1 ms (e.g., after power-up), the first
conversion result should be ignored. This mode makes the
AD7653 ideal for applications where both high accuracy and
fast sample rate are required.
Normal mode is the fastest mode (800 kSPS) without any
limitations on the time between conversions. This mode makes
the AD7653 ideal for asynchronous applications such as data
acquisition systems, where both high accuracy and fast sample
rate are required.
Impulse mode, the lowest power dissipation mode, allows power
saving between conversions. When operating at 1 kSPS, for
example, it typically consumes only 138 µW. This feature makes
the AD7653 ideal for battery-powered applications.
C
LSB
SW
SW
COMP
A
B
SWITCHES
CONTROL
CONTROL
CNVST
LOGIC
OUTPUT
BUSY
CODE
02966-0-005
AD7653