MAX34406 Maxim, MAX34406 Datasheet - Page 9

• Manufacturer Part Number: MAX34406
• Description: The MAX34406 is a quad, high-side, unidirectional, current-sense amplifier that offers precision accuracy
• Manufacturer: Maxim

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 might drift if it is
allowed to heat up excessively. The precision V
device allows the use of small sense resistors to reduce
power dissipation and reduce hot spots.
Because of the high currents that flow through R
take care to eliminate parasitic trace resistance from
causing errors in the sense voltage. Either use a four-
terminal current-sense resistor or use Kelvin (force and
sense) PCB layout techniques.
PCB trace resistance from R
contributes to gain error in the current-sense amplifiers.
Care should be taken to minimize this resistance (shown
as R
trace resistance can be calculated as follows:
For example, assume a gain of 100V/V, as in the
MAX34406H. From
Then every 10mI of PCB trace resistance adds -0.01%
gain error.
When designing a system that uses a sample-and-hold
stage in the ADC, the sampling capacitor momentarily
loads OUTx and causes a drop in the output voltage. If
sampling time is very short (less than a microsecond),
Figure 1. Input Trace Resistance
TRC
in
Figure
Optional Output Filter Capacitor
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1). Total gain including error caused by
R
Table
TRC
Minimizing Trace Resistance
G
Efficiency and Power Dissipation
INx+
with Overcurrent Threshold Comparators
=
MAX34406
1, R1 = 100I and R
R1 R
R
GND
SENSE
R
2
+
OUTx
R losses in R
SENSE
INx-
TRC
OUTx
Kelvin Connections
to the INx+ inputs
LOAD
SENSE
OUTx
OS
= 10kI.
Quad Current-Sense Amplifier
can be
SENSE
of the
,
consider using a ceramic capacitor across OUTx and
GND to hold V
decreases the small-signal bandwidth of the current-
sense amplifier and reduces noise at OUTx.
Some applications of current-sense amplifiers need to
measure currents accurately even in the presence of
both differential and common-mode ripple, as well as a
wide variety of input transient conditions. For example,
high-frequency ripple at the output of a switching buck or
boost regulator results in a common-mode voltage at the
device’s inputs. Alternatively, the fast load-current tran-
sients, when measuring at the input of a switching buck
or boost regulator, can cause high-frequency differential
sense voltages to occur at the device’s inputs, although
the signal of interest is the average DC value. Such high-
frequency differential sense voltages can result in a volt-
age offset at the device output.
The device allows a method of filtering to help improve
performance in the presence of input common-mode
voltage and input differential voltage transients.
shows a differential input filter.
The capacitor C
resistor R
filter against input differential voltages and prevents them
from reaching the device.
The corner frequency of this filter is determined by the
choice of R
at INx- (R1). See
gain options.
The value of R
on the input offset voltage due to the bias current at INx-.
Figure 2. Differential Input Filter
IN
IN
between the sense resistor and INx- helps
, C
IN
OUTx
IN
IN
should be chosen to minimize its effect
Table 1
, and the value of the input resistance
between INx+ and INx- along with the
constant during sampling. This also
INx+
MAX34406
R
SENSE
GND
C
for R1 values at the different
IN
INx-
MAX34406
R
OUTx
IN
Input Filters
LOAD
Figure 2