AD7276BRMZ Analog Devices Inc, AD7276BRMZ Datasheet - Page 16

• Manufacturer Part Number: AD7276BRMZ
• Description: IC ADC 12BIT 3MSPS HS LP 8MSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7276BRMZ

• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Bits: 12
• Sampling Rate (per Second): 3M
• Number Of Converters: 1
• Power Dissipation (max): 19.8mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• Resolution (bits): 12bit
• Sampling Rate: 3MSPS
• Input Channel Type: Single Ended
• Supply Current: 5.5mA
• Digital Ic Case Style: SOP
• No. Of Pins: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7276CBZ - BOARD EVALUATION FOR AD7276
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

AD7276/AD7277/AD7278
THEORY OF OPERATION
CIRCUIT INFORMATION
The AD7276/AD7277/AD7278 are fast, micropower, 12-/10-/
8-bit, single-supply ADCs, respectively. The parts can be operated
from a 2.35 V to 3.6 V supply. When operated from a supply
voltage within this range, the AD7276/AD7277/AD7278 are
capable of throughput rates of 3 MSPS when provided with a
48 MHz clock.
The AD7276/AD7277/AD7278 provide the user with an on-
chip track-and-hold ADC and a serial interface housed in a tiny
6-lead TSOT or an 8-lead MSOP package, which offers the user
considerable space-saving advantages over alternative solutions.
The serial clock input accesses data from the part and provides
the clock source for the successive approximation ADC. The
analog input range is 0 V to V
required for the ADC, and there is no reference on-chip. The
reference for the AD7276/AD7277/AD7278 is derived from the
power supply, resulting in the widest dynamic input range.
The AD7276/AD7277/AD7278 also feature a power-down
option to save power between conversions. The power-down
feature is implemented across the standard serial interface as
described in the Modes of Operation section.
CONVERTER OPERATION
The AD7276/AD7277/AD7278 are successive approximation
ADCs that are based on a charge redistribution DAC. Figure 19
and Figure 20 show simplified schematics of the ADC. Figure 19
shows the ADC during its acquisition phase, where SW2 is closed,
SW1 is in Position A, the comparator is held in a balanced con-
dition, and the sampling capacitor acquires the signal on V
When the ADC starts a conversion, SW2 opens and SW1 moves
to Position B, causing the comparator to become unbalanced
(see Figure 20). The control logic and the charge redistribution
DACs are used to add and subtract fixed amounts of charge
from the sampling capacitor to bring the comparator back into
a balanced condition. When the comparator is rebalanced, the
conversion is complete. The control logic generates the ADC
output code.
V
IN
SW1
A
AGND
B
Figure 19. ADC Acquisition Phase
CAPACITOR
SAMPLING
ACQUISITION
PHASE
V
DD
/2
DD
. An external reference is not
SW2
COMPARATOR
REDISTRIBUTION
CHARGE
CONTROL
DAC
LOGIC
IN
Rev. B | Page 16 of 28
.
ADC TRANSFER FUNCTION
The output coding of the AD7276/AD7277/AD7278 is straight
binary. The designed code transitions occur midway between
successive integer LSB values, such as 0.5 LSB and 1.5 LSB. The
LSB size is V
and V
for the AD7276/AD7277/AD7278 is shown in Figure 21.
TYPICAL CONNECTION DIAGRAM
Figure 22 shows a typical connection diagram for the AD7276/
AD7277/AD7278. V
V
of 0 V to V
with two leading zeros followed by the 12-bit, 10-bit, or 8-bit
result. The 12-bit result from the AD7276 is followed by two
trailing zeros; the 10-bit and 8-bit results from the AD7277 and
AD7278 are followed by four and six trailing zeros, respectively.
Alternatively, because the supply current required by the AD7276/
AD7277/AD7278 is so low, a precision reference can be used as the
supply source for the AD7276/AD7277/AD7278. A REF19x voltage
reference (REF193 for 3 V) can be used to supply the required
voltage to the ADC (see Figure 22). This configuration is especially
useful if the power supply is noisy or the system’s supply voltage is a
value other than 3 V (for example, 5 V or 15 V). The REF19x
outputs a steady voltage to the AD7276/AD7277/AD7278. If the
low dropout REF193 is used, it must supply a current of typically
1 mA to the AD7276/AD7277/AD7278. When the ADC is
converting at a rate of 3 MSPS, the REF193 must supply a maxi-
mum of 5 mA to the AD7276/AD7277/AD7278.
DD
should be decoupled. This provides an analog input range
V
DD
IN
Figure 21. AD7276/AD7277/AD7278 Transfer Characteristics
/256 for the AD7278. The ideal transfer characteristic
SW1
DD
000...010
000...001
000...000
111...111
111...110
111...000
011...111
DD
A
. The conversion result is output in a 16-bit word
/4,096 for the AD7276, V
AGND
B
Figure 20. ADC Conversion Phase
CAPACITOR
0V
SAMPLING
ACQUISITION
REF
0.5LSB
PHASE
V
is taken internally from V
DD
/2
ANALOG INPUT
1LSB = V
1LSB = V
1LSB = V
SW2
COMPARATOR
REF
REF
REF
DD
+V
/4096 (AD7278)
/1024 (AD7277)
/256 (AD7276)
/1,024 for the AD7277,
DD
REDISTRIBUTION
– 1.5LSB
CHARGE
CONTROL
DD
DAC
LOGIC
; therefore,