Datasheet

Input AINx
AVDD
BAT54SWTI
AVSS
10kW
typ.
ADS1158
www.ti.com SBAS429D –JUNE 2008– REVISED MARCH 2011
APPLICATION INFORMATION
c. Input Overload Protection: Overdriving the
multiplexer inputs may affect the conversions of
HARDWARE CONSIDERATIONS
other channels. In the case of input overload,
The following summarizes the design and layout
external Schottky diode clamps and series
considerations when using the ADS1158:
resistor are recommended, as shown in
a. Power Supplies: The converter accepts a single
Figure 49.
+5V supply (AVDD = +5V and AVSS = AGND) or
dual, bipolar supplies (typically AVDD = +2.5V,
AVSS = –2.5V). Dual supply operation
accommodates true bipolar input signals, within a
±2.5V range. Note that the maximum negative
input voltage to the multiplexer is limited to
AVSS – 100mV, and the maximum positive input
voltage is limited to AVDD + 100mV. The range
for the digital power supply (DVDD) is 2.7V to
5.25V. For all supplies, use a 10μF tantalum
Figure 49. Input Overload Protection
capacitor, bypassed with a 0.1μF ceramic
capacitor, placed close to the device pins.
d. ADC Inputs: The external multiplexer loop of the
Alternatively, a single 10μF ceramic capacitor can
ADS1158 allows for the inclusion of signal
be used. The supplies should be relatively free
conditioning between the output of the multiplexer
from noise and should not be shared with devices
and the input of the ADC. Typically, an amplifier
that produce voltage spikes (such as relays, LED
provides gain, buffering, and/or filtering to the
display drivers, etc.). If a switching power supply
input signal. For best performance, the ADC
is used, the voltage ripple should be low (< 2mV).
inputs should be driven differentially. A differential
The analog and digital power supplies may be
in/differential out or a single-ended-to-differential
sequenced in any order.
driver is recommended. If the driver uses higher
b. Analog (Multiplexer) Inputs: The 16-channel
supply voltages than the device itself (for
analog input multiplexer can accommodate 16
example, ±15V), attention should be paid to
single-ended inputs, eight differential input pairs,
power-supply sequencing and potential
or combinations of either. These options permit
over-voltage fault conditions. Protection resistors
freedom in choosing the input channels. The
and/or external clamp diodes may be used to
channels do not have to be used consecutively.
protect the ADC inputs. A 1nF or higher capacitor
Unassigned channels are skipped by the device.
should be used directly across the ADC inputs.
In the Fixed-Channel mode, any of the analog
e. Reference Inputs: It is recommended to use a
inputs (AIN0 to AIN15) can be addressed for the
10μF tantalum capacitor with a 0.1μF ceramic
positive input and for the negative input. The
capacitor directly across the reference pins,
full-scale range of the device is 2.13V
REF
, but the
VREFP and VREFN. The reference inputs should
absolute analog input voltage is limited to 100mV
be driven by a low-impedance source. For rated
beyond the analog supply rails. Input signals
performance, the reference should have less than
exceeding the analog supply rails (for example,
3μV
RMS
broadband noise. For references with
±10V) must be divided prior to the multiplexer
higher noise, external filtering may be necessary.
inputs.
Note that when exiting the sleep mode, the
device begins to draw a small current through the
reference pins. Under this condition, the transient
response of the reference driver should be fast
enough to settle completely before the first
reading is taken, or simply discard the first
several readings.
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