Battery temperature detection and parasitic resistance compensation system
The present application provides systems and methods for battery temperature detection and parasitic resistance compensation. Compensation circuitry is provided to generate a compensation current, proportional to a battery charging or discharging current, to compensate for the parasitic resistance associated with the line connection between a charger/monitor and a battery pack. The compensation current operates to adjust a reference current supplied to a temperature sensor, to enable accurate temperature measurement of the battery pack while reducing or eliminating influence from the parasitic resistance. The compensation circuitry can be utilized in a battery charger topology to enhance battery charging control and/or a battery monitoring topology to enhance battery discharge control.
1. A battery charger system, comprising:
charger controller circuitry configured to generate a controllable charging current to charge a battery coupled to the charger controller, the charger controller comprising a temperature sensing node configured to be coupled to temperature sensor circuitry, associated with the battery, to monitor a voltage drop proportional to the temperature of the battery, wherein when the battery charger circuitry is coupled to the battery, a parasitic resistance is generated; and
compensation circuitry coupled to the temperature sensing node and configured to generate a compensation current that sinks current from the temperature sensing node in an amount proportional to a voltage drop of the controllable charging current across the parasitic resistance,
wherein the charger controller circuitry further comprises current source circuitry configured to supply a temperature sensing current, based on a reference current, to the temperature sensor circuitry, and
wherein the current source circuitry comprises:
amplifier circuitry having a first input configured to receive a reference voltage and a second input coupled to a reference resistor;
a first transistor configured to be controlled by an output of the amplifier circuitry; and
a current mirror, wherein the first transistor is coupled between the current mirror and the reference resistor to generate the reference current, and
wherein the output of the amplifier circuitry controls the resistance of the first transistor so that the voltage at the first input substantially matches the voltage at the second input.
2. The battery charger system of claim 1 , wherein the temperature sensor circuitry comprises a thermistor coupled adjacent to the battery and configured to change resistance in response to a change in temperature of the battery.
3. The battery charger system of claim 1 , wherein the value of the temperature sensing current is determined by the reference current and the compensation current.
4. The battery charger system of claim 1 , further comprising a sense resistor configured to generate a voltage drop proportional to the controllable charging current,
wherein the compensation circuitry comprises an amplifier, a second transistor and a resistor component,
wherein the amplifier has a first input coupled to a first side of the sense resistor and a second input coupled to an output of the second transistor, and the amplifier has an output coupled to the second transistor to control the conduction state of the second transistor,
wherein the second transistor and the resistor component are coupled in series between the temperature sensing node and a second side of the sense resistor, and
wherein the output of the amplifier controls the resistance of the second transistor so that the voltage at the first input of the amplifier substantially matches the voltage at the second input of the amplifier.
5. A battery discharging system, comprising:
monitoring circuitry configured to control a discharge current from a battery, the monitoring circuitry comprising;
a temperature sensing node configured to be coupled to temperature sensor circuitry, associated with the battery, to monitor a voltage drop proportional to the temperature of the battery; and
current source circuitry configured to supply a temperature sensing current, based on a reference current, to the temperature sensor circuitry, wherein when the monitoring circuitry is coupled to the battery, a parasitic resistance is generated; and
compensation circuitry coupled to the current source monitoring circuitry and configured to generate a compensation current that sources current into the current source monitoring circuitry in an amount proportional to a voltage drop of the discharge current across the parasitic resistance,
wherein the current source circuitry comprises:
amplifier circuitry having a first input configured to receive a reference voltage and a second input coupled to a reference resistor;
a first transistor configured to be controlled by an output of the amplifier circuitry; and
a current minor, wherein the first transistor is coupled between the current minor and the reference resistor to generate the reference current, and
wherein the output of the amplifier circuitry controls the resistance of the first transistor so that the voltage at the first input substantially matches the voltage at the second input.
6. The battery discharging system of claim 5 , wherein the temperature sensor circuitry comprises a thermistor coupled adjacent to the battery and configured to change resistance in response to a change in temperature of the battery.
7. The battery discharging system of claim 5 , wherein the value of the temperature sensing current is determined by the reference current and the compensation current.
8. The battery discharging system of claim 5 , further comprising a sense resistor configured to generate a voltage drop proportional to the discharge current,
wherein the compensation circuitry comprises an amplifier, a second transistor and a resistor component,
wherein the amplifier has a first input coupled to a first side of the sense resistor and a second input coupled to an output of the second transistor, and the amplifier has an output coupled to the second transistor to control the conduction state of the second transistor,
wherein the second transistor and the resistor component are coupled in series between the current source monitoring circuitry and a second side of the sense resistor, and
wherein the output of the amplifier controls the resistance of the second transistor so that the voltage at the first input of the amplifier substantially matches the voltage at the second input of the amplifier.
9. A battery charger system, comprising:
charger controller circuitry configured to generate a controllable charging current to charge a battery coupled to the charger controller, the charger controller comprising a temperature sensing node configured to be coupled to temperature sensor circuitry, associated with the battery, to monitor a voltage drop proportional to the temperature of the battery, wherein when the battery charger circuitry is coupled to the battery, a parasitic resistance is generated;
a sense resistor configured to generate a voltage drop proportional to the controllable charging current; and
compensation circuitry comprising an amplifier, a first transistor and a resistor component, wherein the amplifier includes:
a first input coupled to a first side of the sense resistor and a second input coupled to an output of the first transistor; and
an output coupled to the first transistor to control the conduction state of the first transistor,
wherein the first transistor and the resistor component are coupled in series between the temperature sensing node and a second side of the sense resistor, and
wherein the output of the amplifier controls the resistance of the first transistor so that the voltage at the first input substantially matches the voltage at the second input.
10. The battery charger system of claim 9 , wherein the temperature sensor circuitry comprises a thermistor coupled adjacent to the battery and configured to change resistance in response to a change in temperature of the battery.
11. The battery charger system of claim 9 , further comprising temperature sensing circuitry coupled to the temperature sensing node and configured to supply a temperature sensing current to the temperature sensor circuitry.
12. The battery charger system of claim 11 , wherein the charger controller circuitry is further configured to generate a reference voltage,
wherein the temperature sensing circuitry comprises a resistor coupled between the reference voltage and the temperature sensing node to generate a reference current, and
wherein the value of the reference current is determined by the temperature sensing current and the compensation current.
13. The battery charger system of claim 9 , wherein the charger controller circuitry further comprises current source circuitry configured to supply a temperature sensing current, based on a reference current, to the temperature sensor circuitry.
14. The battery charger system of claim 13 , wherein the current source circuitry comprises:
amplifier circuitry having a first input configured to receive a reference voltage and a second input coupled to a reference resistor;
a second transistor configured to be controlled by an output of the amplifier circuitry; and
a current mirror, wherein the second transistor is coupled between the current mirror and the reference resistor to generate the reference current, and
wherein the output of the amplifier circuitry controls the resistance of the second transistor so that the voltage at the first input of the amplifier circuitry substantially matches the voltage at the second input of the amplifier circuitry.
15. A battery discharging system, comprising:
monitoring circuitry configured to control a discharge current from a battery, the monitoring circuitry comprising a temperature sensing node configured to be coupled to temperature sensor circuitry, associated with the battery, to monitor a voltage drop proportional to the temperature of the battery, wherein when the monitoring circuitry is coupled to the battery, a parasitic resistance is generated;
a sense resistor configured to generate a voltage drop proportional to the discharge current; and
compensation circuitry comprising an amplifier, a first transistor and a resistor component,
wherein the amplifier has:
a first input coupled to a first side of the sense resistor, a second input coupled to an output of the first transistor; and
an output coupled to the first transistor to control the conduction state of the first transistor,
wherein the first transistor and the resistor component are coupled in series between the current source monitoring circuitry and a second side of the sense resistor, and
wherein the output of the amplifier controls the resistance of the first transistor so that the voltage at the first input substantially matches the voltage at the second input.
16. The battery discharging system of claim 15 , wherein the temperature sensor circuitry comprises a thermistor coupled adjacent to the battery and configured to change resistance in response to a change in temperature of the battery.
17. The battery discharging system of claim 15 , wherein the monitoring circuitry further comprises current source circuitry configured to supply a temperature sensing current, based on a reference current, to the temperature sensor circuitry.
18. The battery discharging system of claim 17 , wherein the current source circuitry comprises:
amplifier circuitry having a first input configured to receive a reference voltage and a second input coupled to a reference resistor;
a second transistor configured to be controlled by an output of the amplifier circuitry; and
a current mirror, wherein the second transistor is coupled between the current mirror and the reference resistor to generate the reference current, and
wherein the output of the amplifier circuitry controls the resistance of the second transistor so that the voltage at the first input of the amplifier circuitry substantially matches the voltage at the second input of the amplifier circuitry.