AD7778 데이터 시트보기 (PDF) - Analog Devices
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AD7778 Datasheet PDF : 12 Pages
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LC2MOS, High Speed
1-, 4-, and 8-Channel 10-Bit ADCs
AD7776/AD7777/AD7778*
FEATURES
AD7776: 1-Channel
AD7777: 4-Channel
AD7778: 8-Channel
Fast 10-Bit ADC: 2.5 s Worst Case
+5 V Only
Half-Scale Conversion Option
Fast Interface Port
Power-Down Mode
APPLICATIONS
HDD Servos
Instrumentation
GENERAL DESCRIPTION
The AD7776/AD7777/AD7778 are a family of high speed,
multichannel, 10-bit ADCs primarily intended for use in R/W
head positioning servos found in high density hard disk drives.
They have unique input signal conditioning features that make
them ideal for use in such single supply applications.
By setting a bit in a control register within both the four-channel
version, AD7777, and the eight-channel version, AD7778, the
input channels can either be independently sampled or any two
channels can be simultaneously sampled. For all versions, the
specified input signal range is of the form VBIAS ± VSWING.
However, if the RTN pin is biased at, for example, 2 V the
analog input signal range becomes 0 V to +2 V for all input
channels. This is covered in more detail under the section
Changing the Analog Input Voltage Range. The voltage VBIAS is
the offset of the ADC’s midpoint code from ground and is
supplied either by an onboard reference available to the user
(REFOUT) or by an external voltage reference applied to
REFIN. The full-scale range (FSR) of the ADC is equal to
2 VSWING where VSWING is nominally equal to REFIN/2. Addi-
tionally, when placed in the half-scale conversion mode, the
value of REFIN is converted. This allows the channel offset(s)
to be measured.
Control register loading and ADC register reading, channel select
and conversion start are under the control of the µP. The twos
complement coded ADCs are easily interfaced to a standard 16-bit
MPU bus via their 10-bit data port and standard microprocessor
control lines.
The AD7776/AD7777/AD7778 are fabricated in linear compat-
ible CMOS (LC2MOS), an advanced, mixed technology process
that combines precision bipolar circuits with low power CMOS
logic. The AD7776 is available in a 24-lead SOIC package; the
AD7777 is available in both 28-lead DIP and 28-lead SOIC
packages; the AD7778 is available in a 44-lead PQFP package.
*Protected by U.S. Patent No. 4,990,916.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
FUNCTIONAL BLOCK DIAGRAMS
CLKIN
VCC
AIN1
RTN
MUX
REFIN
CONTROL
REGISTER
10
10-BIT
ADCREG1
T/H
ADC
10
DB0–DB9
CREFIN
VBIAS
REFIN
CONTROL LOGIC
VSWING
AGND
REF
AD7776
REFOUT
CS RD WR BUSY/INT
DGND
AGND
CLKIN
VCC
AIN1
AIN2
AIN3
AIN4
MUX T/H
1
1
CONTROL
REGISTER
10-BIT
ADC
ADCREG2
10
ADCREG1
10
DB0–DB9
CREFIN
VBIAS
REFIN
RTN
REFIN
MUX
2
T/H
2
VSWING
AGND
REF
CONTROL LOGIC
AD7777
REFOUT
DGND AGND
CLKIN
VCC
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AIN8
MUX T/H
1
1
CONTROL
REGISTER
10-BIT
ADC
ADCREG2
10
ADCREG1
10
DB0–DB9
CREFIN
VBIAS
REFIN
RTN
MUX T/H
2
2
VSWING
AGND
REF
REFOUT
REFIN
CONTROL LOGIC
AD7778
CS RD WR BUSY/INT DGND AGND
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 2002
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