AD7655AST Analog Devices Inc, AD7655AST Datasheet - Page 14

• Manufacturer Part Number: AD7655AST
• Description: IC ADC 16BIT 1MSPS QUAD 48-LQFP
• Manufacturer: Analog Devices Inc
• Series: PulSAR®r

Specifications of AD7655AST

• 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): 135mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• For Use With: EVAL-AD7655CBZ - BOARD EVALUATION FOR AD7655

AD7655
APPLICATION INFORMATION
CIRCUIT INFORMATION
The AD7655 is a very fast, low power, single-supply, precise
simultaneous sampling 16-bit ADC.
The AD7655 provides the user with two on-chip, track-and-
hold, successive approximation ADCs that do not exhibit any
pipeline or latency, making it ideal for multiple multiplexed
channel applications. The AD7655 can also be used as a
4-channel ADC with two pairs simultaneously sampled.
The AD7655 can be operated from a single 5 V supply and be
interfaced to either 5 V or 3 V digital logic. It is housed in a
48-lead LQFP or a tiny, 48-lead LFCSP that combines space
savings and allows flexible configurations as either a serial or
parallel interface. The AD7655 is pin-to-pin compatible with
PulSAR ADCs.
MODES OF OPERATION
The AD7655 features two modes of operation, normal mode
and impulse mode. Each of these modes is suitable for specific
applications.
Normal mode is the fastest mode (1 MSPS). Except when it is
powered down (PD = HIGH), the power dissipation is almost
independent of the sampling rate.
Impulse mode, the lowest power dissipation mode, allows
power saving between conversions. The maximum throughput
in this mode is 888 kSPS. When operating at 20 kSPS, for
example, it typically consumes only 2.6 mW. This feature makes
the AD7655 ideal for battery-powered applications.
Rev. B | Page 14 of 28
TRANSFER FUNCTIONS
The AD7655 data format is straight binary. The ideal transfer
characteristic for the AD7655 is shown in Figure 16 and Table 7.
The LSB size is 2 × V
Table 7. Output Codes and Ideal Input Voltages
Description
FSR − 1 LSB
FSR − 2 LSB
Midscale + 1 LSB
Midscale
Midscale − 1 LSB
−FSR + 1 LSB
−FSR
1
2
This is also the code for overrange analog input:
(V – V
This is also the code for underrange analog input (V
INx
INxN
111...111
111...110
111...101
000...010
000...001
000...000
above 2 × (V
–FS
–FS + 0.5 LSB
Figure 16. ADC Ideal Transfer Function
–FS + 1 LSB
REF
REF
Analog Input
V
4.999924 V
4.999847 V
2.500076 V
2.5 V
2.499924 V
−76.29 μV
0 V
– V
/65536, which is about 76.3 μV.
REF
REFGND
= 2.5 V
ANALOG INPUT
)).
+FS – 1.5 LSB
Digital Output Code
0xFFFF
0xFFFE
0x8001
0x8000
0x7FFF
0x0001
0x0000
INx
below V
+FS – 1 LSB
1
2
INxN
).