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Texas Instruments 12-V Battery Monitoring in an Automotive Module Application notes
12-V Battery Monitoring in an Automotive Module
Peter Iliya
Monitoring current off an automotive 12-V battery
provides critical data for a variety of applications such
as module current consumption, load diagnostics, and
load feedback control. The TI current sensing portfolio
can address this space with analog and digital current
sense amplifier (CSA) devices that come automotive
qualified, contain integrated features, and operate in
12-V environments even though powered with lowvoltage rails. This document provides recommended
devices and architectures to address current sensing
in this space.
{1.8 V to 5 V}
VS
VBAT
(12 V)
+
OUT
±
Load
Diagnostic
Control /
ADC
GND
Current Sense Amplifier (CSA)
GND
Figure 1. Current Sense Amplifier on 12-V Rail
There are constraints in this space that stem from
conditions such as electrical transient protection
regulations ISO7637-2 and ISO16750-2, jump-starts,
reverse-polarity, and cold-cranking. In general,
system-level protection and suppression schemes can
be used to protect downstream circuitry from these
voltage surge conditions. Types of devices included in
these solutions are smart high-side switches, smart
diodes, or other discrete implementations. These
products may come with internal integrated current
sensing features, but they often are not very accurate
(±3% to ±20% maximum error) and have limited
dynamic range.
Dedicated TI current sensors are low in power
consumption and highly accurate (<1% error) in
automotive environments even across temperature.
A matched internal gain network plus input offset
zeroing provides lower measurement drift across
temperature compared to either discrete solutions or
ICs with supplemental integrated current sensing. This
amplifier integration and technology can remove the
need for temperature and system calibrations, all at
low cost.
Usually, general system protection schemes do not
fully suppress or protect against voltage surges, so
these primary regulations translate into typical voltage
survivability requirements. Depending on the system, a
current sensor may need to survive load dumps,
reverse battery protection, fast load-switching, and
inductive kickback voltages. For example, working on
a 12-V battery rail requires at least 40-V survivability
during load dump conditions. It is important to choose
a current sensor that has an input common-mode
voltage (VCM) rating that complies with the worst-case
VCM condition of the system. Otherwise, input voltage
clamping schemes are needed to protect the device
during such conditions.
There are multiple TI Current (Power) Sensing
amplifiers that can operate on a 12-V automotive
battery and survive crucial voltage levels up to 40 V
and more. Ultimately, they provide very accurate, zerodrift, high bandwidth, and low-cost solutions. Using TI's
Product selection tool online, Table 1 tabulates
candidates for high-side current sensing on an
automotive 12-V battery rail requiring 40-V
survivability. It should be noted that all devices in
Table 1 have multiple gain variants ranging from 20
V/V to 500 V/V.
Table 1. Current Sense Amplifiers for Monitoring 12-V Automotive Battery
TI CURRENT SENSE
AMPLIFIER
VCM
SURVIVABILITY
VOS_MAX
(25 °C)
BW
GAIN ERROR
MAX (25 °C)
IQ_MAX
(25 °C)
FEATURES
INA240-Q1
-6 V to +90 V
±25 µV
400 kHz
±0.2%
2.4 mA
PWM rejection (very high CMRR), AEC Q100 (temperature
grades 1 and 0)
INA190-Q1
-0.3 V to +42 V
±10 µV
45 kHz
±0.3%
65 µA
More accurate version of INA186-Q1. Wide dynamic range.
INA186-Q1
-0.3 V to +42 V
±50 µV
45 kHz
±1%
65 µA
Low input bias current (IB = ±500 pA typical). Wide dynamic
range. Operates with supply voltage (VS) of 1.7 V.
INA180-Q1 (INA181Q1)
-0.3 V to +28 V
±500 µV
350 kHz
±1%
0.5 mA
Single, dual, and quad channel. Uni- or bi-directional versions
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According to Table 1, the INA240-Q1 provides the best
performance, but is not optimized to monitor a 12-V
battery compared to INA186-Q1, which requires less
power, cost, and package size. The INA186-Q1 does
have high AC CMRR (140 dB) and large dynamic
range (VOUT swings to VS - 40 mV over temperature).
Additionally, the INA186-Q1 possesses a unique
capacitively-coupled input architecture that increases
differential input-resistance by 3 orders of magnitude
compared to majority of CSAs. High input-impedance
allows the user to filter current noise at the device
input with minimal effect on gain. Using the datasheet
equation if R1 = 1 kΩ, the effective gain is reduced
43.5 m% for all variants except A1 (25 V/V). Figure 2
shows use of INA186-Q1 in battery monitoring.
Filtering at the input (instead of output) means current
noise is not amplified and the INA186-Q1 can drive a
cleaner signal into the ADC without an output filter
loading down the ADC.
VPEAK G 42 V
f-3dB =
1/(4‹R1C)
VBAT
+
R1 ” 1k
VBAT
RSHUNT
+
RSHUNT
±
±
R1 ” 1k
INA186-Q1
Noisy
load
Load
INA186-Q1
GND
GND
Figure 2. INA186-Q1 On 12-V Battery With and
Without Noise Filtering
The breadth of the current sense portfolio enables the
user to optimize tradeoffs when incorporating common
input protection schemes. If the chosen device states
that the Absolute Maximum Common-Mode Voltage
rating cannot exceed your maximum expected voltage
surge, then it needs input protection. Along with some
passives, the current sensor needs transient voltage
suppression (TVS) or Zener diodes at the inputs for
protection. Figure 3 shows an example using the costoptimized current sensor INA181-Q1.
VPEAK > 28 V
D1
INA181-Q1
R1
VBAT
R2 optional
+
RSHUNT
±
R1
Load
R2 optional
D1
GND
Figure 3. INA181-Q1 with Input Protection for VCM >
28 V
2
In Figure 3, diodes D1 clamp the input VCM of the
device to less than 28 V, which is the absolute
maximum for INA181-Q1. R2 is optional and can be
included to prevent simultaneous turn-on for D1 and
the internal ESD structure of the CSA, but it is usually
not needed. If it is needed, R2 should be small
compared to R1. The power rating of diodes depends
on the maximum expected voltage rise, but more
importantly on the turn-on current. The diode current
can be reduced by increasing R1 resistance, but this
reduces the effective gain of the circuit and, more
critically, increases gain error variation for most current
sensors (except INA186-Q1).
Given the internal resistor gain network and input
differential resistance of the INA181-Q1, an engineer
can calculate the effective circuit gain with R1 using the
equation in the datasheet. Keep in mind that adding
external resistors broaden the system gain error
variance beyond the datasheet limits. This is due to
the fact that INA181-Q1 internal resistors are matched
to be ratiometric, but are not trimmed to their typical
values, so their absolute values can vary by ±20%.
Overall, an engineer can choose the INA181-Q1
because total cost with input protection is lower and
increase in gain error variation is acceptable; however,
devices with higher rated VCM are more straightforward
solutions that provide accurate current sensing over
temperature with less complexity and fewer
components.
Alternate Device Recommendations
See Table 2 for applications that need either larger
VCM ranges or integrated features such as shunt
resistors or comparators.
Table 2. Alternate Device Recommendations
Device
Optimized Parameters
Performance
Tradeoff
INA253
Integrated 2 mΩ shunt resistor (included in Gain Error
spec). Enhanced PWM rejection
IQ
INA301-Q1
BW and slew rate. Internal comparator with adjustable
threshold and 1 µs alert response time
40 V VCM max
INA302-Q1,
INA303-Q1
BW and slew rate. Dual comparator output with
adjustable thresholds and 1 µs alert response time
40 V VCM max
LMP8278QQ1
-12 V to +50 V VCM survivability. Adjustable gain and
filtering. Buffered output
VOS
INA1x8-Q1,
INA1x9-Q1
≥60 VCM. Current output (adjustable gain). Trimmed
input resistors. Low IB when powered off
VOS
Table 3. Related Technical Documentation
TIDA-00302
Transient Robustness for Current Shunt Monitor
SBOA162
Measuring Current To Detect Out-of-Range
Conditions
SBOA165
Precision current measurements on high-voltage
power-supply rails
SBOA167
Integrating the Current Sensing Signal Path
SBAA324
Shunt-based Current-Sensing Solutions for BMS
applications in HEVs and EVs
12-V Battery Monitoring in an Automotive Module Peter Iliya
Copyright © 2019, Texas Instruments Incorporated
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