CN113391252A - Current sensor for mobile charging system - Google Patents
Current sensor for mobile charging system Download PDFInfo
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- CN113391252A CN113391252A CN202010179925.2A CN202010179925A CN113391252A CN 113391252 A CN113391252 A CN 113391252A CN 202010179925 A CN202010179925 A CN 202010179925A CN 113391252 A CN113391252 A CN 113391252A
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- 230000005611 electricity Effects 0.000 claims 1
- 238000010586 diagram Methods 0.000 description 11
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- 238000003869 coulometry Methods 0.000 description 2
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- 238000004364 calculation method Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
- G01R35/005—Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
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Abstract
The invention provides a current sensor for a mobile charging system. It includes shunt resistance, shunt, band gap reference circuit, dynamic calibration circuit and ADC circuit, shunt resistance and removal charging system's power is established ties, the shunt is used for measuring shunt resistance's electric current, dynamic calibration circuit is used for according to band gap reference circuit's reference current corrects measuring current, finally measuring current flow to ADC circuit carries out analog-to-digital conversion and exports. The current sensor adopts a current divider made of a metal layer, and provides a corresponding temperature compensation scheme, so that the accuracy of the sensor can be improved, and a dynamic error correction method is provided, so that an error source of a dynamic band gap reference circuit can be effectively inhibited.
Description
Technical Field
The invention relates to the field of energy storage, in particular to a current sensor for a mobile charging system.
Background
In recent years, energy storage materials have been developed rapidly, and more mobile energy storage is applied. The most widely used method for estimating the state of charge of a battery at present is coulometry. Coulometry determines the net charge flow of a battery by measuring the battery current, but a current sensor is the one that has a critical effect on the current measurement error (gain error or offset). The current loss of the current sensor and the current sensing deviation are preferably lower than the battery self-discharge rate. Assuming a conservative self-discharge rate of 1% per month for the handheld device and a standard battery capacity of 5000mAh, the current deviation required to accurately estimate the battery state of charge is preferably below 50 μ Α. However, if the bi-directional current is as high as ± 7A, the deviation of the existing various current sensors is substantially over 500 μ a, and the gain error is ± 3%. Therefore, the accuracy of the current sensor affects the detection result of the battery charge.
Disclosure of Invention
In order to solve the above-mentioned disadvantages of the prior art, an object of the present invention is to provide a current sensor for a mobile charging system to solve the problem of low accuracy of the current sensor.
The patent provides a current sensor for removing charging system, its characterized in that, including shunt resistance, shunt, band gap reference circuit, dynamic calibration circuit and ADC circuit, shunt resistance is used for establishing ties with the power that removes charging system, the shunt is used for measuring the electric current of shunt resistance, dynamic calibration circuit is used for the basis band gap reference circuit's reference current is rectified the measuring current, the measuring current flow to ADC circuit carries out analog-to-digital conversion and exports.
Preferably, the current sensor is obtained by calculating a shunt resistance, and obtains the shunt resistance RshuntVoltage drop V overshuntThe measurement of the battery current is performed.
Preferably, a shunt made of a metal layer is used, consisting of 4 parallel metal layers (M2-M5) with an area of 600 μ M x 800 μ M and a nominal value of 6M Ω of the shunt.
Preferably, the temperature of the shunt is measured by reusing the PNP transistor of the dynamic bandgap reference circuit, and then the shunt resistance R is dividedshuntThe digital value of the voltage drop is subjected to polynomial correction, so that the influence of dynamic errors is eliminated.
Preferably, the shunt is placed directly on the PNP transistor, and the coupling is further lifted by thermal vias between the shunt and the M1 plane near the PNP transistor.
Preferably, the switch is driven by the lowest voltage, if IbatGround if > 0, or V if Ibat < 0+shunt, to obtain from the output of the ADC the Ibat polarity required for the minimum selection scheme.
Preferably, the bandgap reference circuit provides a reference voltage V for the ADCRefAnd detecting the temperature T required by the shunt temperature compensation scheme, wherein the working specified range of the band gap reference voltage at the minimum power supply voltage of 1.35V is 1.35-1.65V.
Preferably, the permissible digitization temperatures T and V are usedshuntError occurred and by the modified coefficient alpha1And alpha2For temperatures T and VshuntAnd (5) correcting, namely indirectly correcting the curvature g (T) to realize the overall dynamic control.
Meanwhile, the invention also provides a method for correcting data under the condition of the characteristic temperature T, which comprises the following specific steps:
m1: determining VRef，nomA and B, known external voltages are used for ADC, generating muT(T) and μIbat(T)。
M2: determining alpha of a splitter1And alpha2The known current (3A) flows through the shunt, while the ADC is used to measure μT(T) and μIbat(T). The temperature of the shunt is obtained. Will Ibat、VRef，nomAnd muIbatAfter (T) is substituted into the formula, the shunt resistance R can be obtainedshunt。
M3: by making the shunt resistance RshuntDetermination of the temperature coefficient α by fitting to a second order polynomial1And alpha2. After obtaining batch correction data (alpha)1、α2、VRef，nomA and B), the individual chips were calibrated at room temperature.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention adopts the shunt made of the metal layer and provides a corresponding temperature compensation scheme, thereby improving the accuracy of the sensor.
(2) The invention provides a dynamic error correction method which can effectively restrain an error source of a dynamic band gap reference circuit.
Drawings
Fig. 1 is a structural diagram of a current sensor for a mobile charging system according to the present invention;
fig. 2 is a schematic diagram of current acquisition of the current sensor according to the present invention;
fig. 3 is a diagram illustrating a shunt structure of a current sensor for a mobile charging system according to the present invention;
fig. 4 is a schematic diagram of current leakage at the front end of a current sensor for a mobile charging system according to the present patent;
FIG. 5 is a circuit diagram of current leakage suppression on the front end of the sensor provided by this patent;
FIG. 6 is a bandgap reference circuit for a current sensor provided by this patent;
fig. 7 is a circuit diagram of a dynamic calibration circuit provided in this patent.
Detailed Description
To further understand the structure, characteristics and other objects of the present invention, the following detailed description is given with reference to the accompanying preferred embodiments, which are only used to illustrate the technical solutions of the present invention and are not to limit the present invention.
Fig. 1 is a block diagram of a current sensor for a mobile charging system according to the present invention. The current sensor for the mobile charging system comprises a shunt resistor, a current divider, a band-gap reference circuit, a dynamic calibration circuit and an ADC (analog-to-digital converter) circuit. The dynamic calibration circuit is used for correcting the measurement current according to the reference current of the band gap reference circuit, and finally the measurement current is sent to the ADC circuit to be subjected to analog-to-digital conversion for output.
Fig. 2 shows a schematic diagram of current acquisition for a mobile charging system according to the present invention. Wherein the current sensor is obtained by calculating the shunt resistance to obtain the shunt resistance RshuntVoltage drop V overshuntThe measurement of the battery current is performed. The cost is lower when the measurement is carried out by using the methodLow and compatible with standard CMOS processes. However, the main reason why the gain error is large is that RshuntTemperature dependence, and the spread of the ADC reference voltage. Therefore, it is necessary to further compensate for the error.
Fig. 3 is a diagram illustrating a shunt structure of a current sensor for a mobile charging system according to the present invention. In order to be fully compatible with standard packaging processes, shunts made of metal layers are used, which are composed of 4 parallel connected metal layers (M2-M5) with an area of 600 μ M × 800 μ M, which are able to handle relatively large currents (up to 8A) well and to make low ohmic contact with the outside, and which have a nominal value of 6M Ω.
For a standard plastic package (100 ℃/W of connection environment thermal resistance), an 8A current through a 6m Ω shunt would result in a 25 ℃ temperature rise. Significant measurement error can be caused due to the shunt's TCR of 0.35%/deg.c. Therefore, there is a need for an improved dynamic correction of measurement errors using dynamic error correction shunt diffusion to within ± 15%.
To address this error, this patent proposes a temperature compensation scheme that measures the temperature of the shunt by reusing the PNP transistor of the dynamic bandgap reference circuit, and then for VshuntThe digital values of (a) are polynomial corrected to mitigate dynamic error effects.
Under the condition of temperature T, the shunt resistance Rshunt(T) can be approximately expressed as:
Rshunt(T)＝Rshunt(T0_shunt)[1+α1(T-T0_shunt)+α2(T-T0_shunt)2](1)
in the formula, alpha1And alpha2Respectively representing first-order and second-order temperature coefficients of the resistor, wherein the temperature coefficients are constant in a given process; t is0_shuntIndicating the temperature at which the shunt was calibrated. T can be detected by an on-chip PNP transistor0_shuntTherefore, it is not necessary to perform correction in an environment where the temperature is stable, thereby reducing the correction time and cost.
This patent places the shunt directly on the PNP transistor and then utilizes the thermal via lift-off coupling between the shunt and the M1 plane near the PNP transistor. Based on this way the thermal coupling can be enhanced, the enhanced thermal coupling between the shunt and the temperature sensing PNP pipe ensures that the self-heating effect of the shunt can be accurately evaluated. After correction, the accuracy of shunt temperature rise due to joule heating is improved by a factor of 3.
Parasitic resistance is minimized by:
s1: the chip was mounted directly on the PCB and connected to the shunt using 32 short (length < 1mm) and thin (diameter 25 μm) package wires;
s2: the chip was packaged in a smaller (3mm x 6mm x 0.85mm) heat resistant enhanced 32-pin QFN package (HVQFN32) and connected to the shunt using eight short (length about 1mm) and thick (diameter 50 μm) package wires.
Through steps S1 and S2, the total parasitic resistance may be lower than 10m Ω.
As shown in fig. 4, this patent provides a schematic of current leakage at the front end of the sensor. Leakage current IleakFrom IbatInitially, the current flows through the on-resistance R of the input switchON. Assuming that the 4 input switches are all matched, pass RONWill result in a voltage drop across CS1Is subjected to differential error Ve＝2RON*Ileak. To avoid current sensing errors, RshuntThe connected switch should be able to minimize leakage current. I isleakIs Vshunt(or I)bat) Is a non-linear function of (a). If IbatIn the nanoampere range, at high temperatures (> 125 ℃) and negative numbers IbatThis error is particularly pronounced (up to 0.5%) under conditions.
In order to solve the current leakage error, the input switch is implemented by a low leakage high threshold voltage NMOS transistor.
As shown in fig. 5, this patent provides a circuit diagram for suppressing current leakage at the front end of the sensor. Since the leakage phenomenon of the advanced disconnection MOS switch is remarkably reduced, the OFF switch is driven by the lowest voltage if IbatGround if > 0, or V if Ibat < 0+shunt, to obtain from the output of the ADC the Ibat polarity required for the minimum selection scheme. Since its off-resistance is about 15 times higher than that of a normal NMOS transistor, the factor I is reducedleakResulting gain error in worst case conditions: is less than 0.01 percent.
As shown in fig. 6, the present patent provides a bandgap reference circuit for a current sensor. The band-gap reference circuit provides a reference voltage V for the ADCRefAnd detecting the temperature T required by the shunt temperature compensation scheme. Further, the bandgap reference voltage must operate at a minimum power supply voltage of 1.35V (specified range is 1.5V ± 10%). The PNP transistor with the smaller emitter area is used in the invention, the equal PNP transconductance can be obtained, and the total bias current can be minimized, so that the VBE and the delta VBE can be accurately and stably sampled.
As illustrated in fig. 7, the present patent provides a dynamic calibration circuit diagram. To reduce the current I and the diffusion in VBE, the offset of the operational amplifier is reduced by chopping and by applying DEM techniques to the PNP transistor it is ensured that the avbe becomes more accurate. Thus, use of RONA sufficiently low wide MOS switch reduces the occurrence of large errors. However, this method may result in a large leakage current under high temperature conditions. For this purpose, the invention uses a digital-enabled T and VshuntError occurred and by modifying the coefficient alpha in equation (1)1And alpha2For T and VshuntCorrection is performed to indirectly correct the curvature g (T). And the increase in current sensing error is negligible (< 0.01%).
Calibration procedures and digital back-end calculations for the current sensor. It should be noted that the curvature g (t) is not explicitly taken into account when performing the following correction steps. Batch calibration data was obtained by characterizing the chip at temperature T as follows:
m1: determining VRef，nomA and B, knowing the external voltage used for ADC, able to generate μT(T) and μIbat(T). Mu toT(T) is substituted into the following equation:
T＝A*μT-B (2)
in the formula, A is 600, B is 270. Use ofAfter linear fitting, a and B can be obtained. V can be obtained according to formula (3)Ref(T) and a reference voltage V at room temperatureRef，nom。
M2: determining alpha of a splitter1And alpha2The known current (3A) flows through the shunt, while the ADC is used to measure μT(T) and μIbat(T). The temperature of the shunt can be obtained according to equation (3). Will Ibat、VRef，nomAnd muIbatAfter (T) is substituted into the formula, R can be obtainedshunt(T)。
μIbat＝Vshunt/VRef＝Rshunt*Ibat/VRef (3)
M3: by reacting Rshunt(T) determination of the temperature coefficient α by fitting to a second order polynomial1And alpha2. After obtaining batch correction data (alpha)1、α2、VRef，nomA and B), the individual chips were calibrated at room temperature.
By the aid of the method, accuracy of the current sensor for the mobile charging system can be improved.
It should be noted that the above summary and the detailed description are intended to demonstrate the practical application of the technical solutions provided by the present invention, and should not be construed as limiting the scope of the present invention. Various modifications, equivalent substitutions, or improvements may be made by those skilled in the art within the spirit and principles of the invention. The scope of the invention is to be determined by the appended claims.
Claims (9)
1. A current sensor for a mobile charging system, the current sensor comprising a shunt resistor, a shunt, a bandgap reference circuit, a dynamic calibration circuit and an ADC circuit; wherein, the shunt with shunt resistance, band gap reference circuit, dynamic calibration circuit electricity is connected, shunt resistance and mobile charging system's power are established ties, the shunt is used for measuring shunt resistance's electric current, dynamic calibration circuit is used for correcting the measuring current according to band gap reference circuit's reference current, the measuring current reaches ADC circuit carries out analog-to-digital conversion and exports.
2. The current sensor of claim 1, wherein the current sensor is equivalent to a current of a power source of the mobile charging system by measuring a current of the shunt resistor.
3. The current sensor of claim 1, wherein the shunt is made of a metal layer, the shunt consisting of 4 parallel metal layers, the metal layers having an area of 600 μm x 800 μm, the shunt having a nominal value of 6m Ω.
4. The current sensor of claim 1, wherein the dynamic bandgap reference circuit comprises a PNP transistor, and wherein the dynamic bandgap reference circuit measures the temperature of the shunt a plurality of times through the PNP transistor by performing a polynomial correction on the digital value of the voltage drop across the shunt resistance.
5. The current sensor of claim 1, wherein the shunt is placed directly above the PNP transistor, and wherein the shunt and the plane of the PNP transistor are coupled to each other via a thermal via.
6. The current sensor of claim 1, wherein the dynamic calibration circuit employs MOS switches that are voltage driven.
7. The current sensor of claim 1, wherein the bandgap reference circuit provides a reference voltage for the ADC, the bandgap reference circuit is configured to compensate the shunt for temperature, the minimum reference voltage of the bandgap reference circuit is 1.35V, and the operating specification range of the bandgap reference circuit is 1.35-1.65V.
8. The current sensor of claim 1, wherein the current sensor employs digitized temperature to correct for errors in voltage differences generated across the shunt resistor, temperature corrected by modified coefficients, and dynamic control of current measurement achieved by indirect curvature correction.
9. A data correction method for a current sensor according to claim 1, characterized in that the data correction method comprises the steps of:
m1: calculating a temperature condition with known external voltage, resulting in a voltage drop and leakage voltage;
m2: determining the temperature coefficient of the current divider, and calculating the shunt resistance on the assumption that the measured current flowing through the current divider is 3A;
m3: and determining a temperature coefficient suitable for a second-order polynomial through the shunt resistance, and correcting the measurement data of the current sensor at room temperature.
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| CN202010179925.2A CN113391252A (en) | 2020-03-13 | 2020-03-13 | Current sensor for mobile charging system |
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20160059204A (en) * | 2014-11-18 | 2016-05-26 | 현대모비스 주식회사 | Battery sensor for vehicle and mehtod for compensating error of shunt resistor comprised in the sensor |
| CN107728094A (en) * | 2017-10-23 | 2018-02-23 | 宁德时代新能源科技股份有限公司 | Current calibration coefficient measuring device and method, and current detecting device and method |
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2020
- 2020-03-13 CN CN202010179925.2A patent/CN113391252A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20160059204A (en) * | 2014-11-18 | 2016-05-26 | 현대모비스 주식회사 | Battery sensor for vehicle and mehtod for compensating error of shunt resistor comprised in the sensor |
| CN107728094A (en) * | 2017-10-23 | 2018-02-23 | 宁德时代新能源科技股份有限公司 | Current calibration coefficient measuring device and method, and current detecting device and method |
Non-Patent Citations (3)
| Title |
|---|
| 王兴隆等: "巨磁电阻电流传感器空间位置特性调控与校正", 《传感器与微系统》 * |
| 辛守乔等: "巨磁阻传感器输出非线性与温漂的补偿", 《高电压技术》 * |
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