MAX9934FART+TG0Y Maxim Integrated, MAX9934FART+TG0Y Datasheet - Page 16

• Manufacturer Part Number: MAX9934FART+TG0Y
• Description: Special Purpose Amplifiers
• Manufacturer: Maxim Integrated
• Series: MAX9934r

The MAX9934 has extremely low CMOS input-bias cur-
rents at both RS+ and RS- (0.1nA) when the input com-
mon-mode voltage is less than the supply voltage.
When the input common-mode voltage becomes higher
than the supply voltage, it draws the input stage operat-
ing current from RS-, 35µA (typ). RS+ maintains its
CMOS input characteristics.
Low-input-bias currents are extremely useful in design
of input filters for current-sense amplifiers. Input differ-
ential filters are sometimes required to average out
rapidly varying load currents. An example of such load
currents are those consumed by a processor, or
switching power supply. Large bias and offset currents
can interact with resistors used in these external filters
to generate large input offset voltages and gain errors.
For more detailed information, see Application Note
AN3888: Performance of Current-Sense Amplifiers with
Input Series Resistors .
Due to the low-input-bias currents, resistors as large as
10kΩ can be easily used without impact on error speci-
fications with the MAX9934. For applications where the
input common-mode voltage is below V
differential filter can be used. For applications where
the input common-mode voltage extends above V
use a one-sided filter with a capacitor between RS+
and RS-, and a filter resistor in series with RS+ to main-
tain the excellent performance of the MAX9934. See
Figure 7.
For applications where the input common-mode voltage
extends above V
and RS- influences the effective V
voltage drop developed across the trace resistance by
the 35µA input bias current at RS-.
The accuracy of the MAX9934 leads to a wide dynamic
range. This applies to both unidirectional mode and
bidirectional mode. This is made possible in the unidi-
rectional mode because the output maintains gain
accuracy below 1mV as shown in the V
(V
High-Precision, Low-Voltage, Current-Sense Amplifier
with Current Output and Chip Select for Multiplexing
MAX9934
16
OUT
< 5mV) graph in the Typical Operating Char-
Monitoring Very Low Currents
CC
Effect of Input-Bias Currents
, trace resistance between R
OS
error due to the
OUT
CC
PCB Layout
, a balanced
vs. V
SENSE
SENSE
CC
,
acteristics . Extending the useful output below 1mV
makes it possible for the MAX9934 to accurately moni-
tor very low currents.
When the input common-mode voltage is below V
the input bias current of the RS- input drops to the
10pA range, the same range as the RS+ input. This
low-input-bias current in combination with the rail-to-rail
common-mode input range, the extremely high com-
mon-mode rejection, and low V
make it ideally suited for use as a precision instrumen-
tation amplifier. In addition, the MAX9934 is stable into
an infinite capacitive load, allowing filtering flexibility.
Figure 8 shows the MAX9934 in a multiplexed arrange-
ment of strain-gauge amplifiers.
Figure 7. One-Sided Input Filter
CONTROLLER
BUCK
Instrumentation Amplifier
RS+
MAX9934
Use as Precision
OS
of the MAX9934
RS-
Maxim Integrated
ASIC
CC
,