HI7191IBZ-T Intersil, HI7191IBZ-T Datasheet - Page 12

• Manufacturer Part Number: HI7191IBZ-T
• Description: CONV A/D 24BIT SIGMA/DLTA 20SOIC
• Manufacturer: Intersil

Specifications of HI7191IBZ-T

• Number Of Bits: 24
• Data Interface: Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 32.5mW
• Voltage Supply Source: Analog and Digital, Dual ±
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-SOIC (0.300", 7.50mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: HI7191IBZ-TTR

range where the internal operational amplifiers remain in the
linear, high gain region of operation. The HI7191 is designed to
have a range of AV
this range on the V
performance.
Transducer Burn-Out Current Source
The V
source which can be turned on/off via the Control Register.
This current source can be used in checking whether a
transducer has burnt-out or become open before attempting
to take measurements on that channel. When the current
source is turned on an additional offset will be created
indicating the presence of a transducer. The current source is
controlled by the BO bit (Bit 4) in the Control Register and is
disabled on power up. See Figure 7 for an applications circuit.
Digital Section Description
A block diagram of the digital section of the HI7191 is shown
in Figure 8. This section includes a low pass decimation
filter, conversion controller, calibration logic, serial interface,
and clock generator.
MODULATOR
LOAD CELL
FIGURE 7. BURN-OUT CURRENT SOURCE CIRCUIT
INHI
SYNC
CLOCK
FIGURE 8. DIGITAL SECTION BLOCK DIAGRAM
DIGITAL
FILTER
input of the HI7191 contains a 500nA (Typ) current
CM
SS
AND CONTROL
CALIBRATION
+1.8V < V
pin will compromise the device
CONFIGURATION
12
RATIOMETRIC
CM
< AV
SERIAL I/O
DD
GENERATOR
RESET
CLOCK
- 1.8V. Exceeding
V
V
AV
AV
V
CURRENT
V
INLO
INHI
RHI
SOURCE
RLO
SS
DD
HI7191
OSC
OSC
SDO
SDIO
SCLK
CS
DRDY
2
1
HI7191
Digital Filtering
One advantage of digital filtering is that it occurs after the
conversion process and can remove noise introduced during
the conversion. It can not, however, remove noise present
on the analog signal prior to the ADC (which an analog filter
can).
One problem with the modulator/digital filter combination is
that excursions outside the full scale range of the device
could cause the modulator and digital filter to saturate. This
device has headroom built in to the modulator and digital
filter which tolerates signal deviations up to 33% outside of
the full scale range of the device. If noise spikes can drive
the input signal outside of this extended range, it is
recommended that an input analog filter is used or the
overall input signal level is reduced.
Low Pass Decimation Filter
The digital low-pass filter is a Hogenauer (sinc
filter. This filter was chosen because it is a cost effective low
pass decimating filter that minimizes the need for internal
multipliers and extensive storage and is most effective when
used with high sampling or oversampling rates. Figure 9
shows the frequency characteristics of the filter where f
the -3dB frequency of the input signal and f
programmed notch frequency. The analog modulator sends
a one bit data stream to the filter at a rate of that is
determined by:
f
f
The filter then converts the serial modulator data into 40-bit
words for processing by the Hogenauer filter. The data is
decimated in the filter at a rate determined by the CODE
word FP10-FP0 (programed by the user into the Control
Register) and the external clock rate. The equation is:
f
The Control Register has 11 bits that select the filter cutoff
frequency and the first notch of the filter. The output data
update rate is equal to the notch frequency. The notch
frequency sets the Nyquist sampling rate of the device while
the -3dB point of the filter determines the frequency
spectrum of interest (f
10 through 2047 where 10 yields a 1.953kHz Nyquist rate.
The Hogenauer filter contains alias components that reflect
around the notch frequency. If the spectrum of the frequency
of interest reaches the alias component, the data has been
aliased and therefore undersampled.
Filter Characteristics
Please note: We have recently discovered a
performance anomaly with the HI7191. The problem
occurs when the digital code for the notch filter is
programmed within certain frequencies. We believe the
error is caused by the calibration logic and the digital
MODULATOR
MODULATOR
NOTCH
= f
OSC
= f
= 78.125kHz for f
/(512 x CODE).
OSC
/128
S
). The FP bits have a usable range of
OSC
= 10MHz.
N
is the
3
) decimating
June 1, 2006
FN4138.8
C
is