The construction plan of an efficient 2200mah 18650 battery management
system
Suppose you were assigned the task of designing a monitor circuit for a new
and battery-based power system. What strategy would you adopt to optimize the
cost and manufacturability of this design? Initial considerations will be to
determine the preferred structure of the system and the location of the
batteries and associated electronic components. After the basic structure is
clear, the next issue that must be considered is the trade-off and coordination
of the circuit topology, for example, how to optimize the communication and
interconnection of the final product.
The external dimensions of the 2200mah 18650 battery will have a
significant impact on the power system structure. Want to use a large number of
small cells to fit into a complex-shaped 2200mah 18650 battery module (or
2200mah 18650 battery pack)? Or do you need to use batteries with very large
dimensions, which would limit the number of batteries due to weight or cause
other size constraints? This is perhaps the most variable part of the design, as
new 2200mah 18650 battery designs continue to come to market and efforts
continue to make 2200mah 18650 battery modules or packs more consistent with the
overall product concept when integrated into a product. For example, in the case
of a car design, batteries may end up dispersed in certain spaces on the vehicle
that would be inefficiently utilized without the batteries.
Another consideration is the interconnection of test signals and/or
telemetry signals between the 2200mah 18650 battery (or modular 2200mah 18650
battery pack), the 2200mah 18650 battery management system (or its subsystem),
and the end application interface. In most cases, a housing can be made to
integrate some data acquisition circuitry in the 2200mah 18650 battery module or
2200mah 18650 battery pack, so that if replacement is needed, important
information such as production ID, calibration, usage specifications, etc. can
be brought with the replaceable components. Walk. This type of information may
be useful for 2200mah 18650 battery management systems (BMS) or service
equipment and minimizes the number of high-voltage rated wires required in the
wiring harness.
Next, for a given mechanical concept design, the monitoring hardware
topology is determined by the precisely defined number of cells that need to be
supported. In automotive applications, there are typically more than 100 2200mah
18650 battery measurement points in total, and the modularity of the system will
determine how many cells a given circuit system measures. The most common
situation is to separate all batteries into at least two sub-groups by safely
disconnecting "service plugs". By keeping the voltage below 200V during a fault
condition, this approach minimizes the risk of electrocution that service
personnel may encounter. The larger 2200mah 18650 battery pack size means two
separate data acquisition systems, each supporting perhaps 50 2200mah 18650
battery taps. In some cases, all electronic components are on an affordable
printed circuit board, but this requires a large number of interconnects, as
shown in Figure 1(a). Alternatively, the electronic components could be
dispersed and more tightly integrated within the 2200mah 18650 battery module,
but this would require a telemetry linking approach. To achieve reliable data
integrity, remote measurement circuits built into automotive wiring harnesses
must use a ruggedized protocol such as the widely used CAN bus. Although the
real CAN bus interface involves several network layers, the pHY layer can be
easily used to form a BMSLAN structure for efficient communication within the
module. This type of distributed structure is shown in Figure 1(b). This
topology allows the computing workload to be distributed among several small
processors, thereby reducing the required data transfer rate and mitigating EMI
issues that can arise from LAN approaches. The final BMS application interface
is likely to be a CAN bus connection to a main system management processor, and
will need to define (or specify at the outset) specific message
transactions.
Other factors may also affect the physical structure and monitoring
circuitry. In the case of lithium-ion batteries, cell capacity balancing is
required, resulting in additional thermal management issues (heat removal), and
if active balancing is required, power conversion circuitry is required.
Temperature probes are often distributed throughout the module to provide a way
to correlate voltage readings with state of charge, requiring some supporting
circuitry and connection schemes. An often overlooked design consideration is
that 2200mah 18650 battery leakage should be minimal when the product is idle or
stored on shelves prior to installation. In some cases, additional control
wiring is necessary.
Across the structures implemented above, there is a common measurement
functionality building block that includes a multi-channel ADC, safety isolation
barriers, and some degree of local processing. The circuit in Figure 2 shows a
scalable design platform that implements data acquisition functions. In this
diagram, the core component that enables the functionality is Linear
Technology's LTC6803 2200mah 18650 battery pack monitor IC, along with an SpI
data isolator and some optional special-purpose circuitry shown. This circuit
includes the input filter and passive balancing functions, forming a complete
12-cell data acquisition solution. If desired, this type of circuitry can be
simply replicated to support more 2200mah 18650 battery measurement schemes
while sharing the local SpI port of the main microcontroller, which in turn
provides the external CAN bus or other LAN type data link required. need.
A major improvement over previous generation monitoring devices, the
LTC6803 supports power shutdown and/or power from a 2200mah 18650 battery pack
alone. When power is removed from the V+ pin, the 2200mah 18650 battery loading
drops to zero (only nA level semiconductor leakage). Operating power can be
provided by the connected 2200mah 18650 battery pack voltage, or from a separate
source to V+, as long as the voltage is always at least as high as the 2200mah
18650 battery pack. For simplicity, the LTC6803 can also draw power directly
from the 2200mah 18650 battery pack, in which case the lowest power state (i.e.
standby) will draw only 12uA. The LTM2883 data isolator is powered from the main
processor through an internally isolated DC-DC converter, so the device will
automatically power down along with the main processor. A very useful feature of
the LTM2883 is that it can also deliver a lot of host-derived power to isolated
electronic components (i.e., the 2200mah 18650 battery side). A small boost
power supply function component (LT3495-1 in Figure 2) is driven in this way to
independently power the LTC6803 so that the 2200mah 18650 battery provides only
the ADC measurement input current (i.e. <200nA average at active conversion).
This circuit has the absolute lowest parasitic 2200mah 18650 battery leakage
while eliminating any 2200mah 18650 battery operating current mismatch that
could otherwise progressively cause a 2200mah 18650 battery capacity
imbalance.
Suppose you were assigned the task of designing a monitor circuit for a new
and battery-based power system. What strategy would you adopt to optimize the
cost and manufacturability of this design? Initial considerations will be to
determine the preferred structure of the system and the location of the
batteries and associated electronic components. After the basic structure is
clear, the next issue that must be considered is the trade-off and coordination
of the circuit topology, for example, how to optimize the communication and
interconnection of the final product.
The external dimensions of the 2200mah 18650 battery will have a
significant impact on the power system structure. Want to use a large number of
small cells to fit into a complex-shaped 2200mah 18650 battery module (or
2200mah 18650 battery pack)? Or do you need to use batteries with very large
dimensions, which would limit the number of batteries due to weight or cause
other size constraints? This is perhaps the most variable part of the design, as
new 2200mah 18650 battery designs continue to come to market and efforts
continue to make 2200mah 18650 battery modules or packs more consistent with the
overall product concept when integrated into a product. For example, in the case
of a car design, batteries may end up dispersed in certain spaces on the vehicle
that would be inefficiently utilized without the batteries.
Another consideration is the interconnection of test signals and/or
telemetry signals between the 2200mah 18650 battery (or modular 2200mah 18650
battery pack), the 2200mah 18650 battery management system (or its subsystem),
and the end application interface. In most cases, a housing can be made to
integrate some data acquisition circuitry in the 2200mah 18650 battery module or
2200mah 18650 battery pack, so that if replacement is needed, important
information such as production ID, calibration, usage specifications, etc. can
be brought with the replaceable components. Walk. This type of information may
be useful for 2200mah 18650 battery management systems (BMS) or service
equipment and minimizes the number of high-voltage rated wires required in the
wiring harness.
Next, for a given mechanical concept design, the monitoring hardware
topology is determined by the precisely defined number of cells that need to be
supported. In automotive applications, there are typically more than 100 2200mah
18650 battery measurement points in total, and the modularity of the system will
determine how many cells a given circuit system measures. The most common
situation is to separate all batteries into at least two sub-groups by safely
disconnecting "service plugs". By keeping the voltage below 200V during a fault
condition, this approach minimizes the risk of electrocution that service
personnel may encounter. The larger 2200mah 18650 battery pack size means two
separate data acquisition systems, each supporting perhaps 50 2200mah 18650
battery taps. In some cases, all electronic components are on an affordable
printed circuit board, but this requires a large number of interconnects, as
shown in Figure 1(a). Alternatively, the electronic components could be
dispersed and more tightly integrated within the 2200mah 18650 battery module,
but this would require a telemetry linking approach. To achieve reliable data
integrity, remote measurement circuits built into automotive wiring harnesses
must use a ruggedized protocol such as the widely used CAN bus. Although the
real CAN bus interface involves several network layers, the pHY layer can be
easily used to form a BMSLAN structure for efficient communication within the
module. This type of distributed structure is shown in Figure 1(b). This
topology allows the computing workload to be distributed among several small
processors, thereby reducing the required data transfer rate and mitigating EMI
issues that can arise from LAN approaches. The final BMS application interface
is likely to be a CAN bus connection to a main system management processor, and
will need to define (or specify at the outset) specific message
transactions.
Other factors may also affect the physical structure and monitoring
circuitry. In the case of lithium-ion batteries, cell capacity balancing is
required, resulting in additional thermal management issues (heat removal), and
if active balancing is required, power conversion circuitry is required.
Temperature probes are often distributed throughout the module to provide a way
to correlate voltage readings with state of charge, requiring some supporting
circuitry and connection schemes. An often overlooked design consideration is
that 2200mah 18650 battery leakage should be minimal when the product is idle or
stored on shelves prior to installation. In some cases, additional control
wiring is necessary.
Across the structures implemented above, there is a common measurement
functionality building block that includes a multi-channel ADC, safety isolation
barriers, and some degree of local processing. The circuit in Figure 2 shows a
scalable design platform that implements data acquisition functions. In this
diagram, the core component that enables the functionality is Linear
Technology's LTC6803 2200mah 18650 battery pack monitor IC, along with an SpI
data isolator and some optional special-purpose circuitry shown. This circuit
includes the input filter and passive balancing functions, forming a complete
12-cell data acquisition solution. If desired, this type of circuitry can be
simply replicated to support more 2200mah 18650 battery measurement schemes
while sharing the local SpI port of the main microcontroller, which in turn
provides the external CAN bus or other LAN type data link required. need.
A major improvement over previous generation monitoring devices, the
LTC6803 supports power shutdown and/or power from a 2200mah 18650 battery pack
alone. When power is removed from the V+ pin, the 2200mah 18650 battery loading
drops to zero (only nA level semiconductor leakage). Operating power can be
provided by the connected 2200mah 18650 battery pack voltage, or from a separate
source to V+, as long as the voltage is always at least as high as the 2200mah
18650 battery pack. For simplicity, the LTC6803 can also draw power directly
from the 2200mah 18650 battery pack, in which case the lowest power state (i.e.
standby) will draw only 12uA. The LTM2883 data isolator is powered from the main
processor through an internally isolated DC-DC converter, so the device will
automatically power down along with the main processor. A very useful feature of
the LTM2883 is that it can also deliver a lot of host-derived power to isolated
electronic components (i.e., the 2200mah 18650 battery side). A small boost
power supply function component (LT3495-1 in Figure 2) is driven in this way to
independently power the LTC6803 so that the 2200mah 18650 battery provides only
the ADC measurement input current (i.e. <200nA average at active conversion).
This circuit has the absolute lowest parasitic 2200mah 18650 battery leakage
while eliminating any 2200mah 18650 battery operating current mismatch that
could otherwise progressively cause a 2200mah 18650 battery capacity
imbalance.
A convenient feature of the LTC6803 is that it has two free ADC inputs with
similar accuracy to the 2200mah 18650 battery inputs. This convenient feature
allows auxiliary measurements, including temperature, calibration signal, or
load current measurements, to be made with little additional circuitry. A
particularly useful measurement is to use a gated resistor divider to measure
the voltage across the 2200mah 18650 battery pack, as shown in Figure 2 (using a
12:1 ratio, connected to the VTEMp1 input). When the circuit is powered down,
the associated FET is disconnected so that the current measurement does not
unnecessarily tax the battery. Since the filtering of this port can be
customized independently of the 2200mah 18650 battery input, true Nyquist
sampling rates up to 200sps are possible for accurate charge current
calculations. Individual cell measurements can be used to periodically provide
software calibration of the voltage divider across the entire 2200mah 18650
battery pack, eliminating the need for expensive resistors. Another very useful
use of the auxiliary input is to measure a very accurate calibrated power supply
(such as Linear Technology's LT6655-3.3, a reference with 0.025% accuracy), in
which case the software can be Inherent match to channel, corrects for all other
channels. Note that thermistor temperature probes do not have to be referenced
to the 2200mah 18650 battery potential, nor do these probes typically require
12-bit resolution. This type of probe is often suitable for interfacing directly
with a microcontroller, leaving the auxiliary input of the high-performance
LTC6803 free for more demanding functions.
In summary, there are many factors to consider in 2200mah 18650 battery
management system circuits, especially those that determine packaging
limitations. When packaging design ideas come together, it is also important to
consider the structure of the electronic circuitry and information flow (e.g.,
connectorization and wire count) that may also have mechanical effects. Once
these factors are weighed and the package design is mature, simply plug in an
LTC6803 platform and you're ready for a well-established, scalable and
cost-effective data acquisition solution.
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