AS8501 Datasheet, PDF (1/40 Pages) ams AG – High precision voltage and current measurement sensor interface

1.1
AS8501
Preliminary Data Sheet
2 _{High precision voltage and current measurement senso}3 _{r interface}
DATA SHEET
1 Features
ƒ 16 bits resolution
ƒ Differential inputs
ƒ Single + 5V supply
ƒ Low power 15 mW
ƒ SOIC16 package
ƒ Self- and system-calibration
with auto-calibration on power up
ƒ 16 kHz maximum sampling frequency
ƒ Internal temperature measurement
ƒ Internal factory trimmed precision reference
ƒ Programmable current sources
ƒ Digital comparator
ƒ Active wake-up
ƒ PGA gains 1, 6, 24, 50, 100
ƒ Zero offset
ƒ Zero offset TC
ƒ Extremely low noise
ƒ Internal oscillator with comparator for active wake up
ƒ 3-wire serial interface, μP compatible
ƒ Temperature range – 40 to + 125 °C
ƒ Individual 24-bit serial number
2 Applications
ƒ Battery management for automotive systems
ƒ Power management
ƒ mV/µV-meter
ƒ High-precision voltage and current measurement
3 General description
The AS8501 is a complete, low power data acquisition system
for very small signals (i.e. voltages from shunt resistors,
thermocouples) that operates on a single 5 V power supply. The
chip powers up with a set of default conditions at which time it
can be operated as a read-only-converter. Reprogramming is at
any time possible by just writing into two internal registers via
the serial interface.
The AS8501 has four ground refering inputs which can be
switched separately to the internal PGA. Two input channels can
also be operated as a fully differential ground free input. The
system can measure both positive and negative input signals.
The PGA amplification ranges from 6 to 100 which enables the
system to measure signals from 7mV to 120 mV full scale range
with high accuracy, linearity and speed.
The chip contains a high precision bandgap reference and an
active offset compensation that makes the system offset free
(better than 0,5 μV) and the offset-TC value negligible. The built-
in programmable digital filter allows an effective noise
suppression if the high speed is not necessary in the application.
The input noise density is only 35 nV / Hz and due to
ETR
ETS
VBAT
RSHH
RSHL
REF
AGND VDDA VSSA
INTERNAL TEMPERATURE
1.26 V
REFERENCE
INPUT MUX
CHOPPER
PROTECTION
BUF
16 BIT - CONVERTER
PGA
and
LEVEL SHIFT
CALIBRATION
DATA
DSP
CONTROLLER
FILTER
INT. CLOCK
TIMER
COMPARATOR
CURRENT
SOURCES
SERIAL INTERFACE / CONTROL REGISTERS
VDDD
VSSD
CLK
EZPRG
SCLK
SDAT
INTN
Figure 1: Functional Block Diagram
the high internal chopping frequency the system is free of 1/f-noise down
to DC.The 0-10 Hz noise is typical below 1 µV i.e. as good or better than
any other available chopper amplifier.
For high speed synchronous measurements the chip can run in an
automatic switching mode between two input channels with pre-
programmed parameter sets.
The circuit has been optimised for the application in battery management
systems in automotive systems. As a front end data acquisition system it
allows an high quality measurement of current, voltage and temperature
of the battery.
With a high quality 100 μΩ resistor the system can handle the starter
current of up to 1500 A, a continuous current of ± 300 A as well as the
very low idle current of a few mA in the standby mode.
For external temperature measurement the chip can use a wide variety of
different temperature sensors such as RTD, PTC, NTC, thermocouples or
even diodes or transistors. A built-in programmable current source can be
switched to any input and activate these sensors without the need of
other external components.
The measurement of the chip temperature with the integrated internal
temperature sensor allows in addition the temperature compensation of
sensitive parameters which increases the total accuracy considerably.
Sensor specific data can be stored in the internal Zener-Zap memory and
are used to calibrate each measurement in the internal data processing
unit before transmission to the external µC via the serial SDI interface.
The flexibility of the system is further increased by a digital comparator
that can be assigned to any measured property
(current, voltage, temperature) and an active wake-up in the sleep-mode.
All analog input-terminals can be checked for wire break via the SDI-
interface.
Revision 1.1, 04-April-06
www.austriamicrosystems.com
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