參數(shù)資料
型號(hào)： AD7939BCP
廠商： ANALOG DEVICES INC
元件分類： ADC
英文描述： 8-Channel, 1.5 MSPS, 12-Bit and 10-Bit Parallel ADCs with a Sequencer
中文描述： 8-CH 10-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, QCC32
封裝： MO-220-VHHD-2, LFCSP-32
文件頁(yè)數(shù)： 16/32頁(yè)
文件大?。?/td> 1332K
代理商： AD7939BCP
AD7938/AD7939
Preliminary Technical Data
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.
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 below and the functions of the bits are described in
register are all 0s.
Table 6. Control Register Bits
MSB
D11
D10
D9
D8
D7
D6
D5
PM1
PM0
CODING
REF
ADD2
ADD1
ADD0
. At power up, the default bit settings in the control
Table 7
Table 7. Control Register Bit Function Description
Bit No.
Mnemonic 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 8.
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
REF
pin, and if this bit is Logic 1, the internal reference is selected (see
the 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 10. The selected input channel is decoded as shown in
The two mode pins select the type of analog input on the eight V
IN
pins. The AD7938/AD7939 can have either
eight single-ended inputs, four fully differential inputs, four pseudo-differential inputs, or seven pseudo-
differential inputs (see Table 9).
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 10).
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 10).
This bit selects the analog input range of the AD7938/AD7939. If it is set to 0, then the analog input range extends
from 0 V to V
REF
. If it is set to 1, then the analog input range extends from 0 V to 2 × V
REF
. When this range is
selected, AV
DD
must 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
Table 8. Power Mode Selection using the Power Management Bits in the Control Register
PM1
PM0
Mode
Description
0
0
Normal
Mode
0
1
Auto
Shutdown
each conversion. In this mode, all circuitry is powered down.
1
0
Auto
Standby
auto-shutdown mode, but it allows the part to power-up in 1 μsec.
1
1
Full
Shutdown
register is retained.
D4
MODE1
D3
MODE0
D2
SHDW
D1
SEQ
LSB
D0
RANGE
11, 10
PM1, PM0
9
CODING
8
REF
7 to 5
ADD2 to
ADD0
.
4, 3
MODE1,
MODE0
2
SHDW
1
SEQ
0
RANGE
section for more information.
Analog Inputs
Table 9
When operating in normal mode, all circuitry is fully powered up at all times.
When operating in auto-shutdown mode, the AD7938/AD7939 will enter full shutdown mode at the end of
When the AD7938/AD7939 enter this mode, all circuitry is partially powered down. This mode is similar to
When the AD7938/AD7939 enter this mode, all circuitry is powered down. The information in the control
Rev. PrN | Page 16 of 32
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