max9934faua Maxim Integrated Products, Inc., max9934faua Datasheet - Page 15

• Manufacturer Part Number: max9934faua
• Description: High-precision, Low-voltage, Current-sense Amplifier With Current Output And Chip Select For Multiplexing
• Manufacturer: Maxim Integrated Products, Inc.

Three components are to be selected to optimize the
current-sense system: R
MAX9934 gain option (G
Tables 1 and 2 are gain tables for unidirectional and
bidirectional operation, respectively. They offer a few
examples for both MAX9934 options having an output
range of 3.1V unidirectional and ±1.65V bidirectional.
Note that the output current of the MAX9934 adds to its
quiescent current. This can be calculated as follows:
When selecting R
tude of I
power dissipation in R
R
designed for current-sense applications.
Finally, in selecting the appropriate MAX9934 gain option
(G
Once all three component values have been selected in
the current-sense application, the system performance
is represented by:
In a first-order analysis of accuracy there are two
MAX9934 specifications that contribute to output error,
input offset (V
a maximum V
Note that the tolerance and temperature coefficient of
the chosen resistors directly affect the precision of any
measurement system.
At high-current levels, the I
significant. Take this into consideration when choosing
the resistor value and its power dissipation (wattage)
rating. Also, the sense resistor’s value drifts if it is
allowed to self-heat excessively. The precision V
the MAX9934 allows the use of a small sense resistor to
reduce power dissipation and eliminate hot spots.
Due to the high currents that flow through R
care to prevent trace resistance in the load current path
from causing errors in the sense voltage. Use a four ter-
minal current-sense resistor or Kelvin contacts (force
and sense) PCB layout techniques.
High-Precision, Low-Voltage, Current-Sense Amplifier
SENSE
with Current Output and Chip Select for Multiplexing
M
), consider both the required V
is typically a low-value resistor specifically
LOAD
R
SENSE
Efficiency and Power Dissipation
V
OS
OS
I
G
OUT,MAX
OUT
V
M
and the required V
SENSE
) and gain error (GE). The MAX9934 has
of 10µV and a maximum GE of 0.25%.
SENSE
= I
______________________________________________________________________________________
= V
= V
OUT,MAX
SENSE
SENSE,MAX
SENSE
= R
= V
, consider the expected magni-
and
SENSE
M
OUT,MAX
2
:
R losses in R
/V
SENSE
x G
= 25µA/mV or 5µA/mV).
SENSE,MAX
M
x I
/I
SENSE
LOAD,MAX
Kelvin Contacts
x R
LOAD
/R
, R
SENSE
OUT
OUT
OUT
and I
SENSE
Accuracy
SENSE
to manage
, and the
OUT
can be
:
, take
OS
of
Since the MAX9934 is essentially a high-output imped-
ance current-source, its output termination resistor,
R
ADC channel. Most successive approximation register
(SAR) architecture ADCs specify a maximum source
resistance to avoid compromising the accuracy of their
readings. Choose the output termination resistor R
such that it is less than that required by the ADC speci-
fication (10kΩ or less). If the R
source resistance specified, the ADC internal sampling
capacitor can momentarily load the amplifier output
and cause a drop in the voltage reading.
If R
consider using a ceramic capacitor from ADC input to
GND. This input capacitor supplies momentary charge
to the internal ADC sampling capacitor, helping hold
V
period. Use of this capacitor reduces the noise in the
output signal to improve sensitivity of measurement.
Table 1. Unidirectional Gain Table*
* All calculations were made with V
V
Table 2. Bidirectional Gain Table*
* All calculations were made with V
V
nal reference voltage of V
OUT
CC
OH
OUT
MAX9934T
MAX9934F
MAX9934T
MAX9934F
OUT
PART
PART
- V
= 3.1V, V
, acts like a source impedance when driving an
Interfacing the MAX9934 to SAR ADCs
constant to within ±1/2 LSB during the acquisition
OH
is larger than the source resistance specified,
= 3.1V.
OUT(MIN)
V
±11.6
V
SENSE
(mV)
±5.8
±24
±29
±58
±72
SENSE
(mV)
12.4
24.8
62
75
= V
REF
OL
CURRENT
OUTPUT
, and OUT connected to an exter-
= 1.65V through R
±145
±290
±600
±145
±290
±360
CURRENT
(µA)
OUTPUT
(µA)
310
620
310
375
CC
CC
= 3.3V, V
OUT
= 3.3V and V
R
(kΩ)
2.4
OUT
10
10
is larger than the
5
5
4
R
(kΩ)
OUT(MAX)
OUT
10
10
OUT
5
8
OUT(MAX)
.
GAIN (V/V)
250
125
60
50
25
20
= V
GAIN
(V/V)
250
125
50
40
OUT
CC
15
=
-