AD7939 Analog Devices, AD7939 Datasheet - Page 15

• Manufacturer Part Number: AD7939
• Description: 8-Channel, 1.5 MSPS, 10-Bit Parallel ADCs with a Sequencer
• Manufacturer: Analog Devices

Specifications of AD7939

• Resolution (bits): 10bit
• # Chan: 8
• Sample Rate: 1.5MSPS
• Interface: Byte,Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref) p-p,5V p-p,Uni (Vref),Uni (Vref) x 2,Uni 2.5V,Uni 5.0V
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

Data Sheet
ON-CHIP REGISTERS
The AD7938/AD7939 have two on-chip registers that are
necessary for the operation of the device. These are the control
register, which is used to set up different operating conditions,
and the shadow register, which is used to program the analog
input channels to be converted.
Table 7. Control Register Bits
MSB
DB11
PM1
Table 8. Control Register Bit Function Description
Bit No.
11, 10
9
8
7 to 5
4, 3
2
1
0
Table 9. Power Mode Selection Using the Power Management Bits in the Control Register
PM1
0
0
1
1
PM0
0
1
0
1
Mnemonic
PM1, PM0
CODING
REF
ADD2 to
ADD0
MODE1,
MODE0
SHDW
SEQ
RANGE
DB10
PM0
Mode
Normal Mode
Autoshutdown
Autostandby
Full Shutdown
DB9
CODING
Description
Power Management Bits. These two bits are used to select the power mode of operation. The user can choose
between either normal mode or various power-down modes of operation, as shown in Table 9.
This bit selects the output coding of the conversion result. If this bit is set to 0, the output coding is straight
(natural) binary. If this bit is set to 1, the output coding is twos complement.
This bit selects whether the internal or external reference is used to perform the conversion. If this bit is Logic 0, an
external reference should be applied to the V
Reference section.
These three address bits are used to either select which analog input channel is converted in the next conversion if
the sequencer is not used, or to select the final channel in a consecutive sequence when the sequencer is used, as
described in Table 11. The selected input channel is decoded as shown in Table 10.
The two mode pins select the type of analog input on the eight V
single-ended inputs, four fully differential inputs, four pseudo differential inputs, or seven pseudo differential
inputs. See Table 10.
The SHDW bit in the control register is used in conjunction with the SEQ bit to control the sequencer function and
access the SHDW register. See Table 11.
The SEQ bit in the control register is used in conjunction with the SHDW bit to control the sequencer function and
access the SHDW register. See Table 11.
This bit selects the analog input range of the AD7938/AD7939. If it is set to 0, the analog input range extends from
0 V to V
be 4.75 V to 5.25 V if a 2.5 V reference is used; otherwise, care must be taken to ensure that the analog input remains
within the supply rails. See the Analog Inputs section for more information.
REF
Description
When operating in normal mode, all circuitry is fully powered up at all times.
When operating in autoshutdown mode, the AD7938/AD7939 enter full shutdown mode at the end of
each conversion. In this mode, all circuitry is powered down.
When the AD7938/AD7939 enter this mode, all circuitry is powered down except for the reference and
reference buffer. This mode is similar to autoshutdown mode, but it allows the part to power up in 7 µs (or
600 ns if an external reference is used). See the Power Modes of Operation section for more information.
When the AD7938/AD7939 enter this mode, all circuitry is powered down. The information in the control
register is retained.
. If it is set to 1, the analog input range extends from 0 V to 2 × V
DB8
REF
DB7
ADD2
DB6
ADD1
Rev. C | Page 15 of 36
DB5
ADD0
REF
pin. If this bit is Logic 1, the internal reference is selected. See the
CONTROL REGISTER
The control register on the AD7938/AD7939 is a 12-bit, write-
only register. Data is written to this register using the CS and
WR pins. The control register is shown in Table 7 and the
functions of the bits are described in Table 8. At power up, the
default bit settings in the control register are all 0s.
DB4
MODE1
IN
pins. The AD7938/AD7939 can have either eight
DB3
MODE0
REF
. When this range is selected, V
DB2
SHDW
AD7938/AD7939
DB1
SEQ
LSB
DB0
RANGE
DD
must