AD7654 Analog Devices, AD7654 Datasheet - Page 14

• Manufacturer Part Number: AD7654
• Manufacturer: Analog Devices

Specifications of AD7654

• Resolution (bits): 16bit
• # Chan: 4
• Sample Rate: 500kSPS
• Interface: Par,Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref) x 2,Uni 5.0V
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

AD7654
APPLICATION INFORMATION
CIRCUIT INFORMATION
The AD7654 is a very fast, low power, single-supply, precise,
simultaneous sampling 16-bit ADC.
The AD7654 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 AD7654 can also be used as a
4-channel ADC with two pairs simultaneously sampled.
The AD7654 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 tiny 48-lead LFCSP that combines space
savings and allows flexible configurations as either a serial or
parallel interface. The AD7654 is pin-to-pin compatible with
PulSAR ADCs.
MODES OF OPERATION
The AD7654 features two modes of operation, normal and
impulse. Each of these modes is more suitable for specific
applications.
Normal mode is the fastest mode (500 kSPS). 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 444 kSPS. When operating at
10 kSPS, for example, it typically consumes only 2.6 mW. This
feature makes the AD7654 ideal for battery-powered
applications.
Rev. B | Page 14 of 28
TRANSFER FUNCTIONS
The AD7654 data format is straight binary. The ideal transfer
characteristic for the AD7654 is shown in Figure 17 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
This is also the code for underrange analog input (V
(V
INx
– V
INxN
111...111
111...110
111...101
000...010
000...001
000...000
above 2 × (V
–FS
–FS + 0.5 LSB
Figure 17. ADC Ideal Transfer Function
REF
–FS + 1 LSB
REF
/65536, which is about 76.3 μV.
Analog Input
V
4.999924 V
4.999847 V
2.500076 V
2.5 V
2.499924 V
−76.29 μV
0 V
− V
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
).