MAX9937EVKIT+ Maxim Integrated Products, MAX9937EVKIT+ Datasheet - Page 8

• Manufacturer Part Number: MAX9937EVKIT+
• Description: EVAL KIT FOR MAX9937
• Manufacturer: Maxim Integrated Products

Specifications of MAX9937EVKIT+

• Channels Per Ic: 1 - Single
• Amplifier Type: Current Sense
• Output Type: Single-Ended
• -3db Bandwidth: 350kHz
• Current - Output / Channel: 22mA
• Operating Temperature: -40°C ~ 125°C
• Current - Supply (main Ic): 20µA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 5.5 V
• Board Type: Fully Populated
• Utilized Ic / Part: MAX9937
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Slew Rate: -

Automotive Current-Sense Amplifier
with Reverse-Battery Protection
The MAX9937 unidirectional high-side, current-sense
amplifier features a 4V to 28V input common-mode volt-
age range that is independent of supply voltage (V
2.7V to 5.5V). The MAX9937 monitors the current through
a current-sense resistor by converting the sense voltage
to a current output (OUT). Gain is set by the ratio of an
output resistor (R
side current monitoring with the MAX9937 does not inter-
fere with the ground path of the load, making it useful for
a variety of automotive battery/ECU monitoring.
Robust input ESD structure allows input common-mode
voltages to exceed the 28V maximum operating input
range for short durations, making the MAX9937 ideal
for applications that need to withstand short-duration
load-dump conditions. The MAX9937 is able to with-
stand reverse-battery conditions by a suitable choice of
input resistors (R
Mode Voltages > 28V and < 0V section .
The MAX9937 current-sense amplifier operation is best
understood as a specialized op-amp circuit with a
p-channel FET in the feedback path. The op amp
forces a current through an external gain resistor at
RSP (R
its voltage drop equals the voltage drop across the
external sense resistor, R
RSP the same as RSN. An external resistor at RSN
(R
offset voltage due to input bias currents.
The current through R
voltage p-channel FET into an external resistor (R
at OUT. This produces an output voltage whose magni-
tude is given by the following equations:
8
RSN
PIN
_______________________________________________________________________________________
1
2
3
4
5
) has the same value as R
RSP
, see the Typical Application Circuit ) so that
Current-Sense Amplifier Operation
NAME
GND
OUT
RSN
V
RSP
CC
OUT
RSN
) and an input resistor (R
Power Supply. Bypass to GND with a
0.1µF capacitor.
Ground
Current Output
Load-Side Connection Through
External R
Supply-Side Connection Through
External R
, R
RSP
Detailed Description
RSP
SENSE
is now sourced by the high-
). See the Input Common-
RSN
RSP
Pin Description
, making the voltage at
FUNCTION
RSP
Resistor
Resistor
to minimize input
RSP
). High-
CC
OUT
=
)
The gain accuracy is primarily determined by the
matching of the two gain resistors, R
voltage gain error of the MAX9937 is less than 1.5%.
Low temperature drift of input bias currents and input
offset currents minimizes their impact on total input off-
set voltage of the current-sense amplifier.
To measure lower currents more accurately, use a high
value for R
sense voltage that reduces the effect of offset voltage
errors of the internal op amp. In applications monitoring
very high currents, however, R
dissipate the I
dissipation is exceeded, its value may drift or it may fail
altogether, causing large differential voltages to devel-
op between RSP and RSN.
To minimize the effect of input offset voltage by produc-
tion calibration, see the Skewed Input Offset Voltage for
Production Calibration section. This can help reduce
the size of the sense resistor in high-current applica-
tions, as well as measure wide-dynamic-range currents
without sacrificing accuracy.
If I
mize the inductance of R
tial filters (see the Flexible EMI Filtering section) .
Low-inductance metal-film resistors are best suited for
these applications.
Because of the use of op-amp style architecture, calcu-
lation of total input offset voltage involves the same
methodology as is used for any standard op-amp cir-
cuit. Interaction of the input bias currents and tolerance
of the external resistors, combined with the core input
offset voltage of the op amp, are important to consider.
Finally, RSS (root-sum-of-squares) calculation for all
these uncorrelated sources of error gives the final input
offset voltage.
(
SENSE
Calculation of Total Input Offset Voltage
V
OS FINAL
−
Total gain = 20V/V with R
has a large high-frequency component, mini-
SENSE
V
V
SENSE
OUT
)
2
2
Applications Information
R losses. If the resistor’s rated power
=
(
=
. The high value develops a higher
and R
V
V
OS
=
SENSE
I
LOAD
)
2
RSP
+
SENSE
(
I
B
×
×
= 500Ω.
×
R
R
R
Δ
OUT
SENSE
RSP
SENSE
R
and use input differen-
Choosing R
RS
OUT
RSP
)
2
= 10kΩ
+
must be able to
(
and R
Δ
I
B
×
R
OUT
SENSE
RS
)
. The
2