a
2.7 V to 5.5 V, 350 kSPS, 10-Bit
4-/8-Channel Sampling ADCs
AD7811/AD7812
FEATURES
10-Bit ADC with 2.3 s Conversion Time
The AD7811 has Four Single-Ended Inputs that
Can Be Configured as Three Pseudo Differential
Inputs with Respect to a Common, or as Two Independent Pseudo Differential Channels
The AD7812 has Eight Single-Ended Inputs that Can
Be Configured as Seven Pseudo Differential Inputs
with Respect to a Common, or as Four Independent
Pseudo Differential Channels
Onboard Track and Hold
Onboard Reference 2.5 V ؎ 2.5%
Operating Supply Range: 2.7 V to 5.5 V
Specifications at 2.7 V–3.6 V and 5 V ؎ 10%
DSP-/Microcontroller-Compatible Serial Interface
High Speed Sampling and Automatic Power-Down Modes
Package Address Pin on the AD7811 and AD7812 Allows
Sharing of the Serial Bus in Multipackage Applications
Input Signal Range: 0 V to VREF
Reference Input Range: 1.2 V to VDD
GENERAL DESCRIPTION
The AD7811 and AD7812 are high speed, low power, 10-bit
A/D converters that operate from a single 2.7 V to 5.5 V supply.
The devices contain a 2.3 µs successive approximation A/D
converter, an on-chip track/hold amplifier, a 2.5 V on-chip reference and a high speed serial interface that is compatible with the
serial interfaces of most DSPs (Digital Signal Processors) and
microcontrollers. The user also has the option of using an external reference by connecting it to the VREF pin and setting the
EXTREF bit in the control register. The VREF pin may be tied
to VDD. At slower throughput rates the power-down mode may
be used to automatically power down between conversions.
The control registers of the AD7811 and AD7812 allow the
input channels to be configured as single-ended or pseudo
differential. The control register also features a software convert
start and a software power-down. Two of these devices can
share the same serial bus and may be individually addressed in
a multipackage application by hardwiring the device address pin.
The AD7811 is available in a small, 16-lead 0.3" wide, plastic
dual-in-line package (mini-DIP), in a 16-lead 0.15" wide, Small
Outline IC (SOIC) and in a 16-lead, Thin Shrink Small Outline Package (TSSOP). The AD7812 is available in a small,
20-lead 0.3" wide, plastic dual-in-line package (mini-DIP), in a
20-lead, Small Outline IC (SOIC) and in a 20-lead, Thin Shrink
Small Outline Package (TSSOP).
PRODUCT HIGHLIGHTS
1. Low Power, Single Supply Operation
Both the AD7811 and AD7812 operate from a single 2.7 V
to 5.5 V supply and typically consume only 10 mW of power.
The power dissipation can be significantly reduced at
lower throughput rates by using the automatic powerdown mode e.g., 315 µW @ 10 kSPS, VDD = 3 V—see
Power vs. Throughput.
2. 4-/8-Channel, 10-Bit ADC
The AD7811 and AD7812 have four and eight single-ended
input channels respectively. These inputs can be configured
as pseudo differential inputs by using the Control Register.
3. On-chip 2.5 V (± 2.5%) reference circuit that is powered
down when using an external reference.
4. Hardware and Software Control
The AD7811 and AD7812 provide for both hardware and
software control of Convert Start and Power-Down.
FUNCTIONAL BLOCK DIAGRAMS
CREF
REFIN
VDD
1.23V
REF
BUF
CLOCK
OSC
MUX
VDD /3
CREF
DGND
BUF
DOUT
SERIAL
PORT
REFIN
VDD
1.23V
REF
AD7811
CHARGE
REDISTRIBUTION
DAC
VIN1
VIN2
VIN3
VIN4
AGND
DIN
RFS
TFS
SCLK
CONTROL
LOGIC
COMP
A0 CONVST
VIN1
VIN2
VIN3
VIN4
VIN5
VIN6
VIN7
VIN8
AGND DGND
AD7812
CLOCK
OSC
CHARGE
REDISTRIBUTION
DAC
DOUT
SERIAL
PORT
TFS
SCLK
MUX
VDD /3
COMP
DIN
RFS
CONTROL
LOGIC
A0 CONVST
REV. B
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reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
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© Analog Devices, Inc., 2000
