ADS1208
www.ti.com
SBAS348A–MARCH 2005–REVISED MARCH 2005
modulator. An external reference could vary from
0.5V to 3V. The modulator input range is defined to
±VREFIN/20. For a 2.5V reference, the full-scale range
is ±125mV. The REFIN pin is decoupled from the
modulator with a buffer.
also directly proportional to the reference voltage, the
drift of the reference is actually cancelled out. Be
aware that this is only the case if the application is
using IOUT to drive the Hall sensor and if REFIN is
connected to REFOUT.
1
RADJ
YOUT
X
Current Source for the Hall Element
Internal circuitry (see Figure 36) forces the IADJ pin
to a potential of:
This means that trimming the resistor can calibrate
the gain of the entire system. The resistor can be
chosen to be stable over temperature, or to compen-
sate any temperature behavior of the Hall sensor.
VREFOUT
VIADJ + AVDD*
5
DIGITAL OUTPUT
+5V
AVDD
A differential analog input signal of 0V ideally pro-
duces a stream of 1s and 0s that are high 50% of the
time and low 50% of the time. A differential analog
input of +100mV produces a stream of 1s and 0s that
are high 80% of the time. A differential analog input
of –100mV produces a stream of 1s and 0s that are
high 20% of the time. The input voltage versus the
output modulator signal is shown in Figure 37.
VREF/5
RADJ
e.g., 100
for 5mA
VADJ = 0.5V
IADJ
Ω
Ω
RI = 0.3
IOUT
ROUT
DIGITAL INTERFACE
Introduction
Figure 36. Current Source
This means that the voltage drop of the resistor RADJ
The analog signal that is connected to the input of the
delta-sigma modulator is converted using the clock
signal that is applied to the modulator. The result of
the conversion, or modulation, is the output signal
MDATA from the delta-sigma modulator. In most
applications, the two standard signals (MCLK and
MDATA) are provided from the modulator to an ASIC,
FPGA, DSP, or µC (each with an implemented filter,
respectively). A single wire interface is provided in
Mode 2, where the data stream is Manchester
encoded. This configuration reduces the costs for
galvanic isolation.
is equal to the current source reference VADJ
.
VREFOUT
VADJ
+
+ 0.5 V
5
With resistor RADJ placed between AVDD and IADJ, a
current of:
VREFOUT
IOUT
+
ǒ
Ǔ
5 @ RADJ)0.3W
is sourced out of the IOUT pin. The current should be
set between 1mA and 8mA. However, it is also
possible to leave the pin open. As the Hall voltage is
directly proportional to this current, the input voltage
to the modulator VIN is directly proportional to the
internal reference voltage VREFOUT. As the filtered
digital output data word YOUT from the modulator is
The interface also provides the inverted outputs
MDATA and MCLK for the signals MDATA and
MCLK, respectively. These inverted outputs are use-
ful for systems with high common-mode noise at the
digital data transmission. The digital interface is
specified for the voltage range of 2.7V to 5.5V.
Modulator Output
+FS (Analog Input)
−
FS (Analog Input)
Analog Input
Figure 37. Analog Input vs Modulator Output of the ADS1208
16
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