Battery protection circuits

An overvoltage battery protection circuit includes a voltage comparator configured to compare a scaled version of a voltage with a voltage reference and indicate an overvoltage condition when the scaled voltage exceeds the voltage reference. The voltage comparator is powered by a first voltage domain. The circuit further includes a first transistor coupled to an output of the voltage comparator and configured to turn on when the voltage comparator indicates the overvoltage condition and generate an overvoltage signal for at least one external device. The circuit further includes a second transistor coupled to the overvoltage signal and configured to turn on when the overvoltage signal is asserted and force the overvoltage signal to remain asserted independent of the first voltage domain. The first and second transistors are powered by a second voltage domain.

FIELD OF THE DESCRIBED EMBODIMENTS

The described embodiments relate generally to personal electronic devices, and more particularly, to battery protection circuits for personal electronic devices.

BACKGROUND

Generally, high capacity rechargeable batteries are popular choices to power personal electronic devices. Depending upon a particular chemistry of the battery, different over or under-voltage conditions can cause battery failure. For example, in Lithium-ion and Lithium polymer batteries, certain over-voltage conditions may cause battery failure and can result in an explosion. Therefore, the Institute of Electrical and Electronics Engineers (IEEE) has developed a set of standards for rechargeable batteries, in particular IEEE 1725, the entire contents of which are hereby incorporated by reference herein. IEEE 1725 stipulates the necessity for over-voltage protection under a two-component failure. For example, a first failure may include a short circuit across a battery charger (first component) and a second failure may include a failure of a protective circuit integrated with a battery (second component) during the short circuit described above. In this scenario, an appropriate battery protection circuit should be present to overcome the two-component failure.

SUMMARY OF THE DESCRIBED EMBODIMENTS

This paper describes various embodiments that relate to personal electronic devices with rechargeable batteries. In particular, embodiments described herein provide battery protection circuits which overcome and appropriately protect personal electronic devices from component failure in battery charging circuitry.

According to one embodiment of the specification, an overvoltage battery protection circuit includes a voltage comparator configured to compare a scaled version of a voltage with a voltage reference and indicate an overvoltage condition when the scaled voltage exceeds the voltage reference. The voltage comparator is powered by a first voltage domain. The circuit further includes a first transistor coupled to an output of the voltage comparator and configured to turn on when the voltage comparator indicates the overvoltage condition and generate an overvoltage signal for at least one external device. The circuit further includes a second transistor coupled to the overvoltage signal and configured to turn on when the overvoltage signal is asserted and force the overvoltage signal to remain asserted when the first transistor turns off. The first and second transistors are powered by a second voltage domain.

According to another embodiment of the specification, a battery protection system includes a battery charging device, an overvoltage protection integrated circuit (IC) in communication with the battery charging device and configured to receive an overvoltage signal, and an overvoltage battery protection circuit in communication with the battery charging device and the overvoltage protection IC. The overvoltage battery protection circuit includes a voltage comparator configured to indicate an overvoltage condition, and a latch pair of transistors configured to activate in response to the overvoltage condition and force the overvoltage signal to remain asserted until the battery charging device is powered down or replaced.

A method for protecting a rechargeable battery from excessive charging voltage is described. The method is carried out by receiving a first voltage domain, processing the first received voltage domain to produce a second voltage domain, wherein the second voltage domain is coupled to a battery charging circuit and a battery protection circuit, monitoring the second voltage domain with the battery protection circuit, disabling the battery charging circuit through the battery protection circuit when the second voltage domain exceeds a first predetermined voltage, and maintaining the disabling until the first voltage domain is less than a second predetermined voltage.

Other aspects and advantages of embodiments described in the specification will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

In one embodiment of a battery protection system, two voltage nodes can be monitored. A first voltage node can be related to, or coupled to a battery, such as a battery charging voltage. A second voltage node can be a voltage related to a voltage supplied by an external charger, such as the ones often used to supply power for portable computing devices or portable media devices.

If the first voltage node exceeds a first voltage level, the battery protection system can disable battery charging. In one embodiment, battery charging can be disabled by asserting a shutdown signal to a battery charging circuit. After the battery charging is initially disabled, battery charging can be maintained as disabled until the second voltage node is below a second voltage level. In one embodiment, the battery charging is disabled until the second voltage node is approximately 0 volts.

By continually disabling battery charging, a user can be required to remove power from the second voltage node, which in some applications can be accomplished by removing power from the external charger. In one embodiment, such a configuration can protect a battery from receiving hazardous voltages when two components within the battery charging path fail.

Turning toFIG. 1, a schematic of a battery protection system is provided. As illustrated, the system100includes overvoltage protection integrated circuit (IC)101, battery charging device102in communication with the overvoltage protection IC101, and battery103in communication with the battery charging device102.

The system100further includes overvoltage battery protection circuit104in communication with the overvoltage protection IC101and the battery charging device102. The system further includes battery chemistry optimizer105in communication with the battery protection circuit104and the battery103.

The overvoltage protection IC101is configured to receive an overvoltage signal from the battery protection circuit104. The battery protection circuit104is configured to generate the overvoltage signal responsive to a comparison of a scaled version of a voltage with a voltage reference. The overvoltage signal is generated if the scaled voltage exceeds the voltage reference. The battery protection circuit104is configured to force the overvoltage signal to remain asserted until the battery charging device102is powered down or replaced. Responsive to receiving the overvoltage signal, the overvoltage protection IC101is configured to turn off a power supply to the battery charging device102. However, regardless of whether the power supply is turned on or off, the overvoltage signal remains asserted until the battery charging device102is powered down or replaced. This may be facilitated through a latch pair of transistors or other suitable configuration.

The battery chemistry optimizer105is configured to adjust a reference voltage of the battery protection circuit104responsive to battery chemistry information of the battery. Battery chemistry information may be any suitable information, including but not limited to battery type, age, number of charge/discharge cycles, battery chemistry, battery components, or any other desired information. The battery chemistry information may be received directly from the battery103or from an external component. The battery chemistry information may be transmitted over a communication interface, for example, a controller area network (CAN) interface, two-wire interface, I2C interface, single wire interface, system management bus (SMB), or any other suitable interface. The adjustment to the reference voltage of the battery protection circuit may enable increased or reduced overvoltage protection dependent upon the battery chemistry. For example, certain battery types or ages may require increased or reduced voltages which may require a different protection scheme. Thus, the adjustment to the reference voltage of the battery protection circuit104allows a slight change to the protection scheme while still enabling stable overvoltage protection.

Hereinafter, examples of the battery protection circuit104are described in detail below with reference toFIGS. 2-3.

As shown inFIG. 2, the battery protection circuit104includes voltage comparator U1. Voltage comparator U1is configured to have a particular amount of hysteresis (e.g., seeFIG. 4). The voltage comparator U1is configured to compare a scaled version of voltage VCCwith voltage reference Vrefand indicate an overvoltage condition when the scaled voltage exceeds the voltage reference. The voltage comparator is powered by a first voltage domain VCCprovided by the battery charging device102. The scaling of the voltage VCCis facilitated through resistors R1and R2. According to one embodiment, resistor R1is a variable resistor configured to be adjusted by the battery chemistry optimizer105. For example, the resistance seen at resistor R1may be altered based on battery chemistry information as described above. In this manner, the scaling of voltage VCCis adjusted to take into consideration different battery chemistry, age, and other suitable information. The reference voltage Vrefmay be any suitable voltage based on a desired threshold for overvoltage signal generation. According to one embodiment, an appropriate value for the reference voltage Vrefis between about 1 and 1.2 Volts. In yet another embodiment, the reference voltage Vrefcan be determined by a band-gap reference.

As further illustrated the powering of the comparator U1is facilitated through resistor R3, diode D1and decoupling capacitor C2. Furthermore, positive feedback, loop gain, and therefore hysteresis is facilitated through resistors R4and R5, and capacitor C1. The hysteresis as present between reference point V0and VCCis illustrated in detail inFIG. 4.

As further illustrated, the battery protection circuit104also includes a latched pair of transistors Q1and Q2powered from a second voltage domain VNprovided from an external charger. The transistor Q1may be an NPN bipolar junction transistor and the transistor Q2may be a PNP bipolar junction transistor, according to one embodiment. As shown resistor network comprising resistors R6, R7, and R8biases the transistors Q1and Q2such that when transistor Q1is turned on (e.g., due to overvoltage), the overvoltage signalSHDNis generated. Furthermore, the overvoltage signalSHDNwill remain asserted by transistor Q2until VNfalls below a predetermined threshold condition. For example, VNwould fall below the predetermined threshold condition if an external charger supplying current to the battery charging device102were shutdown, removed, or replaced.

As described above, the first transistor Q1is coupled to an output of the voltage comparator U1and configured to turn on when the voltage comparator U1indicates an overvoltage condition. At this stage, the first transistor Q1generates the overvoltage signalSHDN. Furthermore, the second transistor Q2is coupled to the overvoltage signalSHDNand configured to turn on when the overvoltage signal is asserted. The second transistor Q2forces the overvoltage signalSHDNto remain asserted until VINfalls below a predetermined threshold value.

Hereinafter, a more detailed description of the battery charging device102is provided with reference toFIG. 3.

As illustrated, the battery charging device102may include an external power metal-oxide-semiconductor field effect transistor (MOSFET) Q3coupled to external charger301. The external charger301provides VNas described above. The transistor Q3is controlled by overvoltage protection IC101such that the overvoltage protection IC101may shut down power to charging buck303. The battery charging device102further includes inductance L1and capacitor C3configured to supply voltage VCCfor powering the comparator U1.

As further illustrated, the charging buck303can include at least one linear charging element Q4. The linear charging element may, according to one embodiment, be a power MOSFET.

As further illustrated, battery103may include at least one storage element B1coupled to an output of the linear charging device Q4. Therefore, an output of the linear charging device Q4may charge the storage element B1as controlled through switching devices Q5and Q6. Switching devices Q5and Q6may be embodied as power MOSFETS or any other suitable devices. Switching devices Q5and Q6may be controllably turned on/off depending upon a charge state as indicated by fuel gauge302or by an external or internal controller (not illustrated).

Furthermore, the fuel gauge302may provide battery charge state information to the battery chemistry optimizer105such that overvoltage protection values are adjusted. This may be in addition or in combination with the battery chemistry information provided by battery103. Thus, the battery protection circuit104may be adjusted according to whether a battery is entirely discharged, partially charged, mostly charged, or above a threshold charge state. In this manner, better overvoltage protection may be afforded.

FIG. 5is a flow chart of method steps for protecting a battery from excessive charging voltage500in accordance with one embodiment of the specification. Persons skilled in the art will understand that any system configured to perform the method steps in any order is within the scope of this description. The method described herein can be provided by analog type circuits as shown inFIGS. 2 and 3, digital type circuits including analog to digital converters, digital to analog converters, state machines, embedded processors, processors and/or memory. In some embodiments, the method described herein can be provided by a processor executing instructions.

The method begins in step502where the input voltage is received. In one embodiment, this input voltage can be an input voltage that can be provided by the external charger301that can receive a relatively high line voltage (such as 110 volts) and provide a relatively lower voltage such as 15 volts. In one embodiment the external charger301can provide direct current (DC) voltage. In another embodiment, the external charger301can provide alternating current (AC).

The method proceeds to step504where the charging device is enabled. For example, battery charging device102as shown inFIG. 1or charging device303can be enabled. In one embodiment, charging device303supply power to charge the battery103while also supplying power for one or more circuits such as battery protection circuit104. In step506, the output of the charging device, such as charging device303can be monitored. In one embodiment, monitoring can be provided by an analog type of circuit such as comparator U1, or a digital type of circuit such as an analog to digital converter, preferably with an associated sample and hold circuit. In one embodiment, step506can monitor the output of the charging device303by comparing the output of the charging device303to a voltage reference. For example, one output of charging device303can be scaled (as through a voltage divider), and that scaled voltage can be compared to the voltage reference. This voltage scaling can advantageously allow accommodation of different voltages from the charging device303to be compared with a fixed voltage reference, such as a band-gap voltage reference.

In step508, if the output of the charging device303is within range (i.e., the supplied voltage from charging device303is within a proper operating level), then the method can return to step506. On the other hand, if the output of the charging device303is out of operating range, then in step510, the charging device303can be shutdown. In one embodiment, charging device303can be disabled by disrupting a supply voltage to charging device303such as through over voltage protection IC101. A shutdown signal can be provided by battery protection circuit104to over voltage protection IC101. In one embodiment, the shutdown signal can be provided by a latching circuit that can assert a shutdown signal, but does not allow the shutdown signal to be de-asserted unless all power is removed from the circuit.

The method proceeds to step512when an input voltage is monitored. In one embodiment, the input voltage can be VNsupplied by external charger301. In step514, if there is an input voltage present, then the method returns to step512. On the other hand, if there is no input voltage present (VNis effectively 0 volts), then in step516charging device303can be enabled and the method ends. In one embodiment, the shutdown signal can be de-asserted to enable charging device303.