AD7927BRUZ Analog Devices Inc, AD7927BRUZ Datasheet - Page 16

• Manufacturer Part Number: AD7927BRUZ
• Description: IC ADC 12BIT 8CH 200KSPS 20TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7927BRUZ

• 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 ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-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: 1.5mA
• 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: -0.9LSB/1.5LSB
• Integral Nonlinearity Error: ±1LSB
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 20
• Package Type: TSSOP
• Input Signal Type: Single-Ended
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7927CBZ - BOARD EVALUATION FOR AD7927
• Lead Free Status / Rohs Status: Compliant

AD7927
In this mode the power consumption of the part is greatly reduced
with the part entering shutdown at the end of each conversion.
When the Control Register is programmed to move into Auto
Shutdown, it does so at the end of the conversion. The user can
move the ADC in and out of the low power state by controlling
the CS signal.
Powering Up the AD7927
When supplies are first applied to the AD7927, the ADC may
power up in any of the operating modes of the part. To ensure that
the part is placed into the required operating mode, the user
should perform a dummy cycle operation as outlined in Figure 15.
The three dummy conversion operation outlined in Figure 15
must be performed to place the part into the Auto Shutdown
Mode. The first two conversions of this dummy cycle operation
are performed with the DIN line tied high, and for the third con-
version of the dummy cycle operation, the user should write the
desired Control Register configuration to the AD7927 in order to
place the part into the Auto Shutdown mode. On the third CS
rising edge after the supplies are applied, the Control Register
will contain the correct information and valid data will result from
the next conversion.
Therefore, to ensure the part is placed into the correct operating
mode, when supplies are first applied to the AD7927, the user
must first issue two serial write operations with the DIN line tied
high, and on the third conversion cycle the user can then write
to the Control Register to place to part into any of the operating
modes. The user should not write to the Shadow Register until
the fourth conversion cycle after the supplies are applied to the
ADC, in order to guarantee the Control Register contains the
correct data.
If the user wishes to place the part into either the Normal or
Full Shutdown Mode, the second dummy cycle with DIN tied
high can be omitted from the three dummy conversion operation
outlined in Figure 15.
POWER VERSUS THROUGHPUT RATE
In Auto Shutdown Mode, the average power consumption of the
ADC may be reduced at any given throughput rate. The power
saving will depend on the SCLK frequency used, i.e., conversion
time. In some cases where the conversion time is quite a propor-
tion of the cycle time, the throughput rate would need to be
reduced in order to take advantage of the power-down modes.
Assuming a 20 MHz SCLK is used, the conversion time is
DOUT
SCLK
DIN
CS
KEEP DIN LINE TIED HIGH FOR FIRST TWO DUMMY CONVERSIONS
1
Figure 15. To Place AD7927 into the Required Operating Mode after Supplies Are Applied
DUMMY CONVERSION
INVALID DATA
12
16
1
DUMMY CONVERSION
INVALID DATA
–16–
800 ns but the cycle time is 5 ms when the sampling rate is at a
maximum of 200 kSPS. If the AD7927 is placed into shutdown
for the remainder of the cycle time, then on average far less
power will be consumed in every cycle compared to leaving the
device in Normal Mode. Furthermore, Figure 16 shows how as
the throughput rate is reduced, the part remains in its shutdown
longer and the average power consumption drops accordingly
over time.
For example, if the AD7927 is operated in a continuous sampling
mode, with a throughput rate of 200 kSPS and an SCLK of
20 MHz (AV
Mode i.e., if PM1 = 0 and PM0 = 1, then the power consumption
is calculated as follows:
The maximum power dissipation during the conversion time is
13.5 mW (I
from Auto Shutdown is 1 ms and the remaining conversion time
is another cycle, i.e., 800 ns, the AD7927 can be said to dissipate
13.5 mW for 1.8 ms during each conversion cycle. For the remain-
der of the conversion cycle, 3.2 ms, the part remains in Shutdown.
The AD7927 can be said to dissipate 2.5 mW for the remaining
3.2 ms of the conversion cycle. If the throughput rate is 200 kSPS,
the cycle time is 5 ms and the average power dissipated during each
cycle is (1.8/5) ¥ (13.5 mW) + (3.2/5) ¥ (2.5 mW) = 4.8616 mW.
Figure 16 shows the maximum power versus throughput rate
when using the Auto Shutdown mode with 3 V and 5 V supplies.
12
0.01
0.1
10
1
0
Figure 16. Power vs. Throughput Rate
DD
16
DD
= 2.7 mA max, AV
20
= 5 V), and the device is placed in Auto Shutdown
AV
DD
40
= 5V
CONTROL REGISTER IS LOADED ON THE FIRST
12 CLOCK EDGES
1
60
THROUGHPUT – kSPS
DATA IN TO CONTROL REGISTER
80
100
DD
INVALID DATA
= 5 V). If the power-up time
CORRECT VALUE IN CONTROL
REGISTER, VALID DATA FROM
NEXT CONVERSION, USER CAN
WRITE TO SHADOW REGISTER
IN NEXT CONVERSION
120
140
12
160
AV
DD
180
16
= 3V
200
REV. 0