AD9231BCPZ-20 Analog Devices Inc, AD9231BCPZ-20 Datasheet - Page 26

• Manufacturer Part Number: AD9231BCPZ-20
• Description: 12 Bit, 20 MSPS Dual Low Power ADC
• Manufacturer: Analog Devices Inc

Specifications of AD9231BCPZ-20

• Number Of Bits: 12
• Sampling Rate (per Second): 20M
• Data Interface: Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 73.3mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 64-LFCSP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9231
The AD9231 is placed in power-down mode either by the SPI
port or by asserting the PDWN pin high. In this state, the ADC
typically dissipates 2.2 mW. During power-down, the output
drivers are placed in a high impedance state. Asserting the
PDWN pin low returns the AD9231 to its normal operating
mode. Note that PDWN is referenced to the digital output
driver supply (DRVDD) and should not exceed that supply
voltage.
Low power dissipation in power-down mode is achieved by
shutting down the reference, reference buffer, biasing networks,
and clock. Internal capacitors are discharged when entering power-
down mode and then must be recharged when returning to normal
operation. As a result, wake-up time is related to the time spent
in power-down mode, and shorter power-down cycles result in
proportionally shorter wake-up times.
When using the SPI port interface, the user can place the ADC
in power-down mode or standby mode. Standby mode allows
the user to keep the internal reference circuitry powered when
faster wake-up times are required. See the Memory Map section
for more details.
DIGITAL OUTPUTS
The AD9231 output drivers can be configured to interface with
1.8 V to 3.3 V CMOS logic families. Output data can also be
multiplexed onto a single output bus to reduce the total number
of traces required.
The CMOS output drivers are sized to provide sufficient output
current to drive a wide variety of logic families. However, large
drive currents tend to cause current glitches on the supplies
and may affect converter performance.
Applications requiring the ADC to drive large capacitive loads
or large fanouts may require external buffers or latches.
The output data format can be selected to be either offset binary
or twos complement by setting the SCLK/DFS pin when operating
in the external pin mode (see Table 11).
Table 12. Output Data Format
Input (V)
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
Condition (V)
< −VREF − 0.5 LSB
= −VREF
= 0
= +VREF − 1.0 LSB
> +VREF − 0.5 LSB
Offset Binary Output Mode
0000 0000 0000
0000 0000 0000
1000 0000 0000
1111 1111 1111
1111 1111 1111
Rev. A | Page 26 of 36
As detailed in the AN-877 Application Note, Interfacing to High
Speed ADCs via SPI, the data format can be selected for offset
binary, twos complement, or gray code when using the SPI control.
Table 11. SCLK/DFS Mode Selection (External Pin Mode)
Voltage at Pin
AGND
DRVDD
Digital Output Enable Function (OEB)
The AD9231 has a flexible three-state ability for the digital
output pins. The three-state mode is enabled using the OEB pin
or through the SPI interface. If the OEB pin is low, the output
data drivers and DCOs are enabled. If the OEB pin is high, the
output data drivers and DCOs are placed in a high impedance
state. This OEB function is not intended for rapid access to the
data bus. Note that OEB is referenced to the digital output
driver supply (DRVDD) and should not exceed that supply
voltage.
When using the SPI interface, the data outputs and DCO of
each channel can be independently three-stated by using the
output disable (OEB) bit (Bit 4) in Register 0x14.
TIMING
The AD9231 provides latched data with a pipeline delay of
9 clock cycles. Data outputs are available one propagation
delay (t
Minimize the length of the output data lines and loads placed
on them to reduce transients within the AD9231. These
transients can degrade converter dynamic performance.
The lowest typical conversion rate of the AD9231 is 3 MSPS. At
clock rates below 3 MSPS, dynamic performance can degrade.
Data Clock Output (DCO)
The AD9231 provides two data clock output (DCO) signals
intended for capturing the data in an external register. The CMOS
data outputs are valid on the rising edge of DCO, unless the DCO
clock polarity has been changed via the SPI. See Figure 2 and
Figure 3 for a graphical timing description.
PD
) after the rising edge of the clock signal.
Twos Complement Mode
1000 0000 0000
1000 0000 0000
0000 0000 0000
0111 1111 1111
0111 1111 1111
SCLK/DFS
Offset binary (default)
Twos complement
SDIO/DCS
DCS disabled(default)
DCS enabled
OR
1
0
0
0
1