Texas Instruments | Turbo Mode 1.0 Setup Steps | Application notes | Texas Instruments Turbo Mode 1.0 Setup Steps Application notes

Texas Instruments Turbo Mode 1.0 Setup Steps Application notes
Application Report
SLUA803 – December 2016
Turbo Mode 1.0 Setup Steps
Swaminathan Ramanathan
ABSTRACT
This document details the method used to obtain and implement the Turbo Mode 1.0 parameters required
to accurately determine peak power deliverables from a power source (battery pack).
1
2
3
Contents
Introduction ................................................................................................................... 2
Setup Steps................................................................................................................... 2
Turbo Mode 1.0 SBS Commands ......................................................................................... 8
List of Figures
1
2
3
4
.....................................................................................
Measuring High-Frequency Resistance ..................................................................................
Measuring Pack and System Resistance.................................................................................
Measuring Cell Interconnect Resistance .................................................................................
Computing Turbo Adjustment Factor
3
5
6
7
List of Tables
1
Min Turbo Power............................................................................................................. 2
2
Max C-Rate ................................................................................................................... 2
3
Turbo Adjustment Factor
4
Reserve Energy %........................................................................................................... 3
5
High-Frequency Resistance ................................................................................................ 4
6
Pack Resistance ............................................................................................................. 5
7
System Resistance .......................................................................................................... 6
8
Cell 1 to 4 Interconnect Resistance ....................................................................................... 6
9
Term Voltage ................................................................................................................. 7
10
Gauging Configuration ...................................................................................................... 7
...................................................................................................
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1
Introduction
1
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Introduction
Turbo Mode 1.0, along with a combination of 8 SBS commands and 10 data flash registers, allows the
bq40zxx gas gauge to provide necessary data for the MCU. The MCU must decide what level of peak
power consumption can be exercised without causing a system reset, or transient battery voltage level
excursion to trigger termination flags.
2
Setup Steps
An example of implementation in the bq40z DF registers is referenced as follows (all values must
correspond to the customer configuration of number of cells and measurements made in the following
section). These values must be set up for the proper operation of Turbo Mode 1.0.
• Min Turbo Power
Minimum Turbo mode level after all higher levels are disabled (expected at the end of discharge, see
Table 1). The negative value is expected. Units: cW.
Table 1. Min Turbo Power
Class
Gas Gauging
•
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Turbo Cfg
Min Turbo
Power
I2
–32767
32767
0
cW
This value is application dependent, and the customer must determine at which power level turbo
mode will no longer be applicable in their application. The default is set to 0 only as a demonstration of
the Turbo mode down to 0 power, but typically this is a nonzero negative value equal to the base
discharge power.
10 mSec Max C-Rate
Maximum discharge current for 10 ms (see Table 2). Units: 0.1C-Rate Ω
Table 2. Max C-Rate
Class
Gas Gauging
•
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Turbo Cfg
10 mSec Max
C-Rate
I1
–12.7
0
–4.0
0.1 C-Rate
This value is typically set to –4.0C. This value is used to guide the maximum peak power (MPP) of the
system (for 10 ms). If required, this value can be adjusted to better reflect the application requirements
for the discharge rate that must be sustained for 10 ms.
Turbo Adjustment Factor
The resistance correction factor, that if used would be a one-time adjustment that the customer would
compute from a 10-s pulse test (see Table 3). Units: none
Table 3. Turbo Adjustment Factor
Class
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Gas Gauging
Turbo Cfg
Turbo
Adjustment
Factor
U1
0.5
1.5
1.00
—
Turbo adjustment factor is a data flash parameter used to enhance the accuracy of the reported peak
powers and currents. This parameter is defined as the ratio of the reported sustained peak power
(SPP) to the applied power, or the sustained peak power current (SPPC) to the applied current at the
instant when the system voltage becomes equal to the minimum system voltage (DF. Term Voltage).
This adjustment factor is modified by the user if the reported SPP or SPPC exceeds the applied power
or current, which causes the system voltage to hit termination. This factor is primarily used to account
for the error associated with the 10-second effective resistance arising from the unaccounted rate
dependence.
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Setup Steps
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Figure 1 shows a scenario where the gauge over estimates the SPPC. The turbo adjustment factor can
be computed from a 10-second pulse test. The reported SPPC consists of two parts: the first part
which is constrained by the maximum discharge rate (until around the 5-hour mark), and the remaining
part where the reported SPPC is the current that causes the system voltage to reach termination. The
ends of the pulses, marked in squares and circles, indicate where the system voltage hits termination.
In this particular scenario, it can be seen that the system voltage hits termination even while the SPPC
is confined by the maximum discharge rate (square) which is an indication of a slightly high error.
Because the true SPPC, which causes system shutdown, is not reported during this time, it is
important to not choose this SPPC (square), to compute the adjustment factor; instead choose the
SPPC that is responsible for voltage termination (circle). The adjustment factor can be computed at the
end of each pulse (circle) as the ratio of the reported SPPC (red) to that of the applied current (blue).
The user must write the worst (highest) value in the data flash.
Figure 1. Computing Turbo Adjustment Factor
•
Reserve Energy %
Energy that remains at the present average discharge rate (as defined in DF.Load Select) until the
maximal peak power reaches the value reported by the MAX_POWER command (see Table 4).
Table 4. Reserve Energy %
Class
Gas Gauging
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Turbo Cfg
Reserve
Energy %
I1
0
100
2
%
This value is a safety factor to ensure that there is some head room with respect to the predicted SPP
and MPP. The default value of 2% works well for most systems.
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Setup Steps
•
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High-Frequency Resistance
Cell high-frequency resistance (see Table 5), Units: mΩ
Table 5. High-Frequency Resistance
Class
Gas Gauging
•
•
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Turbo Cfg
HighFrequency
Resistance
I2
0
32767
20
mΩ
The procedure to obtain the high-frequency cell resistance RHF parameter follows (see Figure 2).
If the ID was released for this cell:
– Obtain RHF from the chemistry selection table. Divide the value by the number of parallel cells used.
If the chem. ID selection procedure is set up by the customer, the following procedure is required:
1. Perform the selection test like before using rel-dis-rel, and select chem. ID using the mathcad tool.
2. Perform a 4C, 10-ms pulse discharge test, and collect 1 ms or higher sampled data with the
oscilloscope (see reference waveform).
3. Use Equation 1 to find high-frequency resistance:
Rhf _ cell _ mOhm = (1000 * (Vbefore _ pulse – V _ end _ of _ pulse ) / (I before _ pulse – I _ pulse )) – Rsys _ mOhm – Rpack _ mOhm) / N _ serial _ cells
(1)
4. Pulse must have a 10-ms duration, and measure at the load terminals (so the discharge path
includes R(sys) and R(pack)).
The setup guidelines:
– Discharge current: C/4 rate
– Pulse duration: 10 ms with 4C discharge
– Pulse frequency: 1 second
– Sampling rate: 1 ms or higher
– Voltage measurement performed at load inputs (same point used earlier to find system resistance)
– If the customer does not have an oscilloscope that can collect data, 10-ms capable load, or has
some difficulty with this test, do the following:
• Send the cell to TI.
• TI runs the OCV/relaxation test with HF sampling.
• The results are used to obtain both the chem. ID selection and RHF value.
• The RHF value and ID selection is sent to customer.
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Setup Steps
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Figure 2 is a point of reference for voltage and current measurements for the high-frequency
resistance RHF measurements.
0.0
I_before
7.5
V_before
Current (A)
Voltage (V)
-5
7.0
-10
V_end_of_pulse
6.5
I_pulse
6.0
-15
0.01
0.02
0.03
Time (seconds)
Figure 2. Measuring High-Frequency Resistance
Calculation method for RHF parameter:
1000 ´
High _ Frequency _ Re sis tance =
•
V _ before - V _ end _ of _ pulse
- Rsys - Rpack
I _ before - I _ pulse
N _ serial
(2)
– Voltage is measured in volts
– Current is measured in amperes
– R(sys) is measured in mΩ
– R(pack) is measured in mΩ
– N_serial is the number of cells in series
– Resulting high-frequency resistance is in mΩ
Pack Resistance
Initial value of Pack Resistance (see Table 6). Units: mΩ
Table 6. Pack Resistance
Class
Gas Gauging
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Turbo Cfg
Pack
Resistance
I2
0
32767
30
mΩ
How to measure R(pack) for the pack side resistance parameter follows (see Figure 3).
– A to B: Measure the impedance from the positive terminal of the cell pack on the PCB (point B) to
the Pack+ connector pin on the pack side of the PCB (point A).
– Factors to consider when obtaining this parameter:
• Total RDS(on) of CHG + DSG FETs for Tj = 125C (from data sheet or measured value)
• R(cell) resistance is factored in the RLF and RHF DF registers
– C to D: Measure the impedance from the negative terminal of the cell pack (point C) on the PCB to
the Pack– connector pin on the pack side of the PCB (point D).
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Setup Steps
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A
H
G
Rtrace_sys
Rtrace_pack
PACK+
+
Voltage Reg
V (minimum)
VMIN_SYS
FETs RDS(ON)
Connector
Interface
F
-
B
Rcell
Rcell
CPU
Rsense
C
EC
Fuel Gauge
Rtrace_pack
Connector
Interface
Rtrace_sys
PACK-
D
E
R(pack) Resistance = A to B + C to D
R(sys) Resistance = E to F + G to H
Figure 3. Measuring Pack and System Resistance
•
System Resistance
Initial value of system resistance (see Table 7). Units: mΩ
Table 7. System Resistance
Class
Gas Gauging
•
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Turbo Cfg
System
Resistance
I2
0
32767
0
mΩ
How to measure R(sys) for the system-side resistance parameter follows (see Figure 4).
– G to H: Measure the impedance from the Pack+ connector pin on the system side of the PCB (point
H) to voltage regulator positive input of Vcore supply (point G).
– E to F: Measure the impedance from the voltage regulator negative pin of Vcore supply (point F) to
Pack– of connector (point E).
Cell 1 to 4 Interconnect Resistance
Interconnects between cells must be measured from the point where the measurement line branches
out to the top of the lower cell and separately to the bottom of the next cell (see Table 8). Units: mΩ
Table 8. Cell 1 to 4 Interconnect Resistance
6
Class
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Gas Gauging
Turbo Cfg
System
Resistance
I2
0
32767
0
mΩ
Turbo Mode 1.0 Setup Steps
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Setup Steps
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To determine the cell interconnect resistance, the following resistance must be measured in the
configuration of the circuit.
H
BAT
G
F
E
VC3
VC2
D
C
VC1
A
Rsense
B
Cell Side of Sense
Resistor
Cell 1 Interconnect Resistance = A to B + (C to D) /2
Cell 2 Interconnect Resistance = (C to D) /2 + (E to F) /2
Cell 3 Interconnect Resistance = (E to F) /2 + G to H
Figure 4. Measuring Cell Interconnect Resistance
NOTE: C, E, and G are the points where the Cell +ve is going to the gauge voltage measurement,
and not the Cell +ve tabs.
•
How to measure the cell 1 to 4 interconnect resistance parameter follows:
– A to B: Measure the impedance from the Rsens connector on the cell side of the PCB (point A) to
Cell1 –ve tab (point B).
– C to D: Measure the impedance from the Cell1 +ve tab that goes to the bq40zxx device pin VC1
(point C) to Cell2 –ve tab (point D).
– E to F: Measure the impedance from the Cell2 +ve tab that goes to the bq40zxx device pin VC2
(point E) to Cell3 –ve tab (point F).
– G to H: Measure the impedance from the Cell3 +ve tab that goes to the bq40zxx device pin VC3
(point G) to BAT (point H).
Term Voltage
The minimum voltage in which the system still operates at the system power converter input (see
Table 9). A capacity gauging algorithm uses this value to converge to 0 remaining capacity at this
voltage. This value is also used to compute MAX_POWER. Term Voltage can be overwritten with
command MIN_SYS_V. Units: mV.
Table 9. Term Voltage
•
Class
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Gas Gauging
IT Cfg
Term Voltage
I2
0
32767
9000
mV
Gauging Configuration: TDELTAV
1: Enable calculating Delta Voltage, which corresponds to the power spike defined in DF.Min Turbo
Power (see Table 10).
0: Enable use of DF.Delta Voltage learned as maximal difference between the instantaneous and
average voltages.
Location: Settings, Configuration, IT Gauging Configuration, 2 bytes, bit 13 (lowest bit counted as zero)
Table 10. Gauging Configuration
Class
Settings
Subclass
Name
Type
Minimum
Maximum
Default
Unit
Configuration
IT Gauging
Config
H2
0x0
0xFFFF
0x5FE
Hex
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Turbo Mode 1.0 SBS Commands
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3
Turbo Mode 1.0 SBS Commands
3.1
AC Peak Power Mode (Turbo Mode 1.0)
The bq40zxx supports Turbo mode 1.0 operation by providing the host MCU with information about the
ability of the battery pack to deliver peak power. This method of operation is based on the host MCU
reading register 0x59 (MAX_POWER) to determine if the selected power level for Turbo mode is below
the maximum power reported by the gas gauge. Several data flash registers are associated with the Turbo
mode operation. A listing of the registers for system configuration follows. The following additions to the
extended SBS commands are required to implement this feature.
• MaxPeakPower()
Block read: command 0x59
Reads the maximum peak power value (cW) for the 10-ms pulse occurring on top of a pulse of
magnitude DF.Ten Second Max C Rate. The gauge computes a new RAM value, MaxPeakPower,
every second. The value is expected to be negative. MaxPeakPower is initialized to present the value
of MaxPeakPower on reset or power up. The intended use of this command is for the system to read
the value for maximum peak power and to decide on switching to a system operation mode with power
requirements below the value for reported maximum peak power.
• MPPCurrent()
Block read: command 0x5e
Reads the maximum peak current value, MPPCurrent (mA), that can occur on top of a pulse of
magnitude DF. Ten Second Max C Rate. The gauge computes a new RAM value, MPPCurrent, every
second. The value is expected to be negative. MPPCurrent is initialized to present the value of
MPPCurrent on reset or power up. The intended use of this command is for the system to read the
maximum peak current and to make a decision about switching to a current mode below the reported
maximum peak current value.
• PackResistance()
Block read/write: command 0x5b
Read/write in Unsealed mode, Read in Sealed mode
Sets the RAM value of the battery pack serial resistance that includes FETs, traces, sense resistor,
and so on, inside the battery pack R(pack), in mΩ. PackResistance() is initialized to data flash value:
DF.Pack Resistance. Writing to this command overwrites the DF value.
• SysResistance()
Block read/write: command 0x5c
Read/write in Unsealed mode, Read in Sealed mode
Sets the RAM value of the system serial resistance along the path from the battery to the system
power converter input that includes FETs, traces, and so on, R(sys), in mΩ. SysResistance() is initialized
to data flash value: DF.System Resistance. Writing to this command overwrites the DF value.
• MinSysVoltage7()
Block write: command 0x5d
Read/write
Sets the minimum voltage at the system power converter input in which the system still operates, in
mV. MIN_SYS_V is initialized to data flash the value: DF.Terminate Voltage. Writing to this command
overwrites the DF value. The intended use of this command is to write it once on the first use to adjust
for possible changes in the system design from the time the battery pack was designed.
• TURBO_FINAL()
Block write: command 0x60
Read/write
Sets the DF.Min Turbo Power, which represents the minimum turbo-mode power level during active
operation (nonsleep), after all higher turbo-mode levels are disabled (expected at the end of
discharge), Unit: cW. A negative value is expected. Writing to this command overwrites the DF value.
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Turbo Mode 1.0 Setup Steps
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