AD7923BRUZ Analog Devices Inc, AD7923BRUZ Datasheet - Page 14

• Manufacturer Part Number: AD7923BRUZ
• Description: IC ADC 12BIT 4CH W/SEQ 16TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7923BRUZ

• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Bits: 12
• Sampling Rate (per Second): 200k
• Number Of Converters: 1
• Power Dissipation (max): 7.5mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP (0.173", 4.40mm Width)
• Resolution (bits): 12bit
• Sampling Rate: 200kSPS
• Input Channel Type: Single Ended
• Supply Voltage Range - Analog: 2.7V To 5.25V
• Supply Current: 2.7mA
• Number Of Elements: 1
• Resolution: 12Bit
• Architecture: SAR
• Sample Rate: 200KSPS
• Input Polarity: Unipolar
• Input Type: Voltage
• Rated Input Volt: 2.5/5V
• Differential Input: No
• Power Supply Requirement: Analog and Digital
• Single Supply Voltage (typ): 3/5V
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 5.25V
• Dual Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Power Dissipation: 7.5mW
• Differential Linearity Error: ±1.5LSB
• Integral Nonlinearity Error: ±1LSB
• Operating Temp Range: -40C to 125C
• Operating Temperature Classification: Automotive
• Mounting: Surface Mount
• Pin Count: 16
• Package Type: TSSOP
• Input Signal Type: Single-Ended
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7923CBZ - BOARD EVAL FOR AD7923
• Lead Free Status / Rohs Status: Compliant

AD7923
THEORY OF OPERATION
CIRCUIT INFORMATION
The AD7923 is a high speed, 4-channel, 12-bit single-supply
ADC. The part can be operated from a 2.7 V to 5.25 V supply.
When operated from either a 5 V or 3 V supply, the AD7923 is
capable of throughput rates of 200 kSPS. The conversion time
can be as short as 800 ns when provided with a 20 MHz clock.
The AD7923 provides the user with an on-chip track-and-hold
ADC and with a serial interface housed in a 16-lead TSSOP
package. The AD7923 has four, single-ended input channels
with a channel sequencer, allowing the user to select a channel
sequence through which the ADC can cycle with each conse-
utive CS falling edge. The serial clock input accesses data from
the part, controls the transfer of data written to the ADC, and
provides the clock source for the successive approximation
ADC. The analog input range is 0 V to REF
REF
register. For the 0 to 2 × REF
from a 4.75 V to 5.25 V AV
The AD7923 provides flexible power management options to
allow the user to achieve the best power performance for a
given throughput rate. These options are selected by program-
ming the power management bits, PM1 and PM0, in the control
register.
CONVERTER OPERATION
The AD7923 is a 12-bit successive approximation ADC based
around a capacitive DAC. It can convert analog input signals in
the range 0 V to REF
Figure 14 show simplified schematics of the ADC. The ADC is
comprised of a control logic, SAR, and capacitive DAC, which
are used to add and subtract fixed amounts of charge from the
sampling capacitor to bring the comparator back into a balanced
condition. Figure 13 shows the ADC during its acquisition phase.
SW2 is closed and SW1 is in Position A. The comparator is held
in a balanced condition and the sampling capacitor acquires the
signal on the selected V
When the ADC starts a conversion (see Figure 14), SW2 opens
and SW1 moves to Position B, causing the comparator to
become unbalanced. The control logic and the capacitive DAC
are used to add and subtract fixed amounts of charge from the
sampling capacitor to bring the comparator back into balance.
V
V
IN
IN
AGND
0
3
IN
, depending on the status of the RANGE bit in the control
SW1
A
Figure 13. ADC Acquisition Phase
B
IN
or 0 V to 2 × REF
IN
channel.
SW2
4kΩ
DD
IN
supply.
range, the part must be operated
COMPARATOR
IN
. Figure 13 and
IN
or 0 V to 2 ×
CAPACITIVE
DAC
CONTROL
LOGIC
Rev. B | Page 14 of 24
When the comparator is rebalanced, the conversion is complete.
The control logic generates the ADC output code. Figure 16 and
Figure 17 show the ADC transfer functions.
Analog Input
Figure 15 shows an equivalent circuit of the analog input
structure of the AD7923. The two diodes D1 and D2 provide
ESD protection for the analog inputs. Care must be taken to
ensure that the analog input signal never exceeds the supply
rails by more than 200 mV; otherwise these diodes become
forward-biased and start conducting current into the substrate.
10 mA is the maximum current these diodes can conduct
without causing irreversible damage to the part. Capacitor C1,
shown in Figure 15, is typically around 4 pF and can primarily
be attributed to pin capacitance. The resistor R1 is a lumped
component made up of the on resistance of the track-and-hold
switch and includes the on resistance of the input multiplexer.
The total resistance is typically about 400 Ω. Capacitor C2 is the
ADC sampling capacitor and has a capacitance of 30 pF typi-
cally. For ac applications, removing high frequency components
from the analog input signal is recommended by using an RC
low-pass filter on the relevant analog input pin. In applications
where harmonic distortion and the signal-to-noise ratio are
critical, the analog input should be driven from a low impe-
dance source. Large source impedances significantly affect the
ac performance of the ADC. This may necessitate the use of an
input buffer amplifier. The choice of the op amp is a function of
the particular application.
When no amplifier is used to drive the analog input, the source
impedance should be limited to low values. The maximum
source impedance depends on the amount of THD that can be
tolerated. The THD increases as the source impedance increases
and performance degrades (see Figure 8).
V
V
IN
IN
AGND
0
3
V
IN
4pF
C1
SW1
A
Figure 15. Equivalent Analog Input Circuit
Figure 14. ADC Conversion Phase
B
D1
D2
AV
DD
SW2
4kΩ
CONVERSION PHASE: SWITCH OPEN
TRACK PHASE: SWITCH CLOSED
COMPARATOR
R1
CAPACITIVE
30pF
C2
DAC
CONTROL
LOGIC