AD7654 Data Sheet
Rev. D | Page 14 of 27
APPLICATIONS 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.
TRANSFER FUNCTIONS
The AD7654 data format is straight binary. The ideal transfer
characteristic for the AD7654 is shown in Figure 18 and Table 7.
The LSB size is 2 × V
REF
/65536, which is about 76.3 µV.
000...000
000...001
000...010
111...101
111...110
111...111
ANALOG INPUT
+FS – 1.5 LSB
+FS – 1 LSB
–FS + 1 LSB–FS
–FS + 0.5 LSB
ADC CODE (Straight Binary)
03057-017
Figure 18. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Description
Analog Input
V
REF
= 2.5 V Digital Output Code
FSR − 1 LSB 4.999924 V 0xFFFF
1
FSR − 2 LSB 4.999847 V 0xFFFE
Midscale + 1 LSB 2.500076 V 0x8001
Midscale 2.5 V 0x8000
Midscale − 1 LSB 2.499924 V 0x7FFF
−FSR + 1 LSB −76.29 µV 0x0001
−FSR 0 V 0x0000
2
1
This is also the code for overrange analog input
(VINx – VINxN above 2 × (VREF − VREFGND)).
2
This is also the code for underrange analog input (V
INx
below V
INxN
).
