Abstract:
In one embodiment of the cold end switch battery management control method, a battery generates an output voltage at a positive terminal thereof. A first control voltage is also generated by an integrated circuit. A gate of a field effect transistor (FET) receives the first control voltage, wherein the FET comprises a drain and a source with the source coupled to a negative terminal of the battery. The FET transmits current towards the battery in response to the gate receiving the first control voltage, wherein the first control voltage is greater than the output voltage, and wherein the first control voltage is less than a breakdown voltage of the integrated circuit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Mobile devices including smart phones, laptop computers, tablet computers, etc., can be powered by rechargeable battery packs that contain one or more rechargeable batteries such as lithium ion batteries. Lithium ion batteries provide several advantages and disadvantages over other types of rechargeable batteries. Lithium ion batteries tend to be lighter, provide higher energy densities, and have a slower loss of charge when not in use. On the other hand, if overcharged, lithium ion batteries may combust. Further, a deep discharge of lithium ion batteries below a voltage threshold (e.g., 2.4 volts-2.8 volts per cell, depending on the chemistry) may result in a dead battery. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]    The present invention may be better understood in its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. 
           [0003]      FIG. 1  is a block diagram illustrating an example battery pack. 
           [0004]      FIG. 2A  illustrates in block diagram relevant components of an example Gate Drive: GD circuit that can be employed in the battery management control (BMC) circuit of  FIG. 1 . 
           [0005]      FIG. 2B  graphically illustrates voltage Vd generated by the GD circuit of  FIG. 2A . 
           [0006]      FIG. 3A  illustrates in block diagram relevant components of an example GD circuit that can be employed in the BMC circuit of  FIG. 1 . 
           [0007]      FIG. 3B  graphically illustrates voltage Vd generated by the GD circuit of  FIG. 3A . 
           [0008]      FIG. 4A  illustrates in block diagram relevant components of an example GD circuit that can be employed in the BMC circuit of  FIG. 1 . 
           [0009]      FIG. 4B  graphically illustrates voltage Vd generated by the GD circuit of  FIG. 4A . 
           [0010]      FIG. 5A  illustrates in block diagram relevant components of an example GD circuit that can be employed in the BMC circuit of  FIG. 1 . 
           [0011]      FIG. 5B  graphically illustrates voltage Vd generated by the GD circuit of  FIG. 5A . 
           [0012]      FIG. 6A  illustrates in block diagram relevant components of an example GD circuit that can be employed in the BMC circuit of  FIG. 1 . 
           [0013]      FIG. 6B  graphically illustrates voltage Vd generated by the GD circuit of  FIG. 6A . 
           [0014]      FIG. 7A  illustrates in block diagram relevant components of an example GD circuit that can be employed in the BMC circuit of  FIG. 1 . 
           [0015]      FIG. 7B  graphically illustrates voltage Vd generated by the GD circuit of  FIG. 7A . 
           [0016]      FIG. 8A  illustrates in block diagram relevant components of an example GD circuit that can be employed in the BMC circuit of  FIG. 1 . 
           [0017]      FIG. 8B  graphically illustrates voltage Vd generated by the GD circuit of  FIG. 8 . 
       
    
    
       [0018]    The use of the same reference symbols in different drawings indicates similar or identical items. 
       DETAILED DESCRIPTION 
       [0019]      FIG. 1  illustrates in block diagram form, relevant components of an example rechargeable battery pack  100  that can power a mobile device such as a smart phone (not shown). Battery pack  100  includes a battery management and control (BMC) circuit  102 , a lithium ion battery cell (hereinafter battery)  104 , a sense resistor  106 , and transistors  108  and  110  that are cascade connected in the “cold end” or the portion of the current loop between the negative terminal of battery  104  and V− of battery pack  100 . 
         [0020]    BMC circuit  102  may take form in one integrated circuit formed on a single substrate or multiple integrated circuits formed on respective substrates. For purposes of explanation only, BMC circuit  102  is presumed to be formed on a single substrate. The present invention will be described with reference to a battery pack that contains a single, rechargeable lithium ion battery or cell, it being understood that the present invention should not be limited thereto. Also for purposes of explanation only, transistors  108  and  110  will take form in n-channel, metal oxide semiconductor field effect transistors (MOSFETs). N-channel MOSFETs have a lower source to drain ON resistance when compared to p-channel MOSFETS. 
         [0021]    BMC circuit  102  can monitor, manage, and control battery cell  104 . For example, BMC circuit  102  can monitor current flow into or out of a battery cell  104  while it is being charged or discharged. Excessive current flow can damage battery cell  104 . If the monitored current flow exceeds a predetermined value, BMC circuit  102  can deactivate or turn off transistor  108  and/or  110 . BMC circuit  102  can also monitor the voltage of battery  104  to ensure that it does not fall outside a range, which is presumed to be 2.5-4.2 volts, while battery  104  is being charged or discharged. If BMC circuit  102  determines that battery voltage Vb exceeds 4.2 volts or is less than 2.5 volts, BMC circuit  102  can deactivate transistor  108  and/or  110 . Additional functions of BMC circuit  102  are contemplated. 
         [0022]    BMC circuit  102  activates (i.e., turns on) transistor  108  and/or transistor  110  by applying a gate voltage that exceeds a threshold value. The present invention will be described with reference to BMC circuit  102  activating transistor  110  while battery  104  is being discharged, it being understood that the present invention should not be limited thereto. When active, the transistor  110  can transmit discharge current between its source and drain. 
         [0023]    A resistance Rdson to current flow exists between the drain and source of transistor  110 . The magnitude of Rdson is dependent upon several factors including the magnitude of the voltage applied to the gate. A lower gate voltage can increase Rdson and vice versa. As will be more fully described, Rdson may adversely affect operational aspects of battery pack  100 . 
         [0024]    BMC circuit  102  can activate transistor  110  by simply connecting Vb, the voltage of battery  104 , to the gate. In this configuration, however, Vb may decrease from its upper limit of 4.2 volts to its lower limit of 2.5 volts while battery  104  discharges. The decrease in voltage may increase Rdson, which increases power consumed by transistor  110 , which in turn reduces the power that can provided to the mobile device. An increase in Rdson also increases the voltage drop across active transistor  110 , which effectively reduces the magnitude of the output voltage of across V+ and V−. 
         [0025]    To reduce adverse effects associated with Rdson, BMC circuit  102  may include one or more sub-circuits that generate and apply a voltage Vd to the gate of transistor  110 . Vd may exceed Vb, the voltage of battery  104 . However, there may be limits on Vd. BMC circuit  102  may have an absolute maximum voltage that should not be exceeded during operation. BMC circuit  102  may be fabricated using a standard complementary metal-oxide-semiconductor (CMOS) process that has an intrinsic breakdown voltage associated with it. If the breakdown voltage is exceeded, permanent damage may result to one or more of devices (e.g., diodes, transistors, etc.) of the circuit. A manufacturer of an integrated circuit, such as BMC  102 , may specify an absolute maximum voltage or breakdown voltage that can be applied. Vd, the voltage generated by BMC circuit  102 , should not exceed the breakdown voltage. 
         [0026]    The figures below illustrate relevant components of example gate driver (GD) circuits that can be employed in BMC circuit  102  for generating and applying Vd to the gate of transistor  110 . The voltage generated by the GD circuit may also be applied to the gate of transistor  108 , or alternatively the gate of transistor  108  may be controlled by a voltage generated by a separate, but similar or identical GD circuit.  FIG. 2A  shows in block diagram relevant components of GD circuit  202 . GD circuit  202  has an input coupled to battery  104  and an output node “d” coupled to the gate of transistor  110 . 
         [0027]    GD circuit  202  includes capacitors C 1  and C 2  coupled to Schottky diodes  204  and  206 , respectively, as shown. The input to diode  204  is coupled to Vb, while the output of diode  206  is coupled to capacitor C 2  and output node d. Capacitor C 1  is coupled to an output of inverter  208 , which is driven by oscillator  210 , which in turn generates a square wave with a voltage that varies between ground and Vb. Although not shown, another component of BMC circuit  102  may deactivate transistor  110  when, for example, Vb drifts outside a predetermined voltage range, which for the purposes of this explanation will be 2.5 volts-4.2 volts. 
         [0028]    GD circuit  202  employs a type of charge pump, which is a DC-to-DC converter that uses one or more capacitors as energy storage elements to create an output voltage (e.g., Vd) that is higher than an input voltage (e.g., Vb). Usually, charge pump circuits use some form of switching device to control the connection of an input voltage to a capacitor. For example, a two-stage cycle can be used. In the first stage of the cycle, a capacitor is connected across a supply that provides the input voltage, thereby charging the capacitor to that same voltage. In the second stage of the cycle, the charge pump circuit is reconfigured so that the same capacitor is in series with the supply voltage, effectively doubling the voltage at a terminal of the capacitor. 
         [0029]    GD circuit  202  can generate voltage Vd at output node d that is greater in magnitude than battery voltage Vb. Specifically, GD circuit  202  can generate Vd=2Vb−2Vf, where Vf represents a voltage drop (approximately 0.3 volts) across Schottky diode  204  or  206 .  FIG. 2B  graphically illustrates the relationship between Vd and Vb for the range 2.5 volts-4.2 volts. Since the gate of transistor  110  is driven by Vd=2Vb−2Vf, Rdson of transistor  110  should be lower than it would be if the gate was driven only by Vb. A lower Rdson results in a lower voltage drop across transistor  110  in addition to a lower consumption of power by transistor  110 . Unfortunately, if Vb is approximately 3.5 volts or greater, GD circuit  202  may generate Vd with a magnitude that exceeds the breakdown voltage (e.g., 6.5 volts) for BMC circuit  102 . 
         [0030]      FIG. 3A  illustrates another GD circuit  302  that could be employed in the BCM circuit  102  of  FIG. 1 . GD circuit  302  operates in one of two different modes depending on the magnitude of Vb. When Vb is greater than a reference voltage VR 1 , GD circuit  302  operates in the first mode and generates Vd=Vb, which does not exceed the breakdown voltage. When Vb is below the reference voltage VR 1 , GD circuit  302  operates in the second mode and generates Vd=Vb+Vf. (herein Vf is forwarding voltage of body diode( 314 ) of p-ch MOSFET ( 310 )). Because BMC circuit  102  limits Vb to the range of 2.5 volts-4.2 volts, Vd will not exceed the breakdown voltage of 6.5 volts in either the first or second mode of operation. 
         [0031]    GD circuit  302  includes several components of GD circuit  202 , such as diodes  204  and  206 , capacitors C 1  and C 2 , and oscillator  210 . A comparator  306  compares Vb with reference voltage VR 1  (presumed to be 3.5 volts). If Vb is greater than a reference voltage VR 1 =3.5 volts, the output of comparator  306  is driven high, which in turn activates p-channel, metal oxide field effect transistor  310  via inverter  312  and deactivates inverter  304 . In this first mode of operation, GD circuit  302  generates Vd=Vb. The second mode of operation is triggered when Vb drops below VR 1 . More particularly, when Vb falls below the reference voltage VR 1 =3.5 volts, the output of comparator  306  will be driven low, which in turn deactivates transistor  310  via inventor  312 , and activates inverter  304 . In this mode, the body diode  314  of transistor  310  acts as a clamp, and GD circuit  302  generates Vd=Vb+0.7.  FIG. 3B  graphically illustrates the relationship between Vd and Vb in both modes of operation. This graph shows the effect of transition between modes when Vb drops below VR 1 =3.5 volts. VR 1  should be selected to be at the lower range of voltages that can activate transistor  110  with an acceptably low Rdson (e.g., a Rdson that doesn&#39;t, for example, consume too much power when the discharge current Idischarge flows). 
         [0032]      FIG. 4A  illustrates another GD circuit  402  that could be employed in the BCM circuit  102  of  FIG. 1 . GD circuit  402  is similar to GD circuit  302  with Schottky diodes  204  and  206  replaced with normal PN junction diodes  205  and  207 . In  FIG. 4A , GD circuit  402  includes a Schottky diode  406  coupled between output d and transistor  310 , and the reference voltage VR 1  is increased to VR 1 =3.7 volts. Schottky diode  406  prevents the clamp circuit mentioned above with respect to GD circuit  302 . When Vb is above the reference voltage VR 1 =3.7 volts, the output of comparator is driven high, which activates transistor  310  and deactivates inverter  304 . In this mode of operation GD circuit  402  generates Vd=Vb−Vf. (herein Vf is a schottky diode forwarding voltage of ˜0.3V) When Vb drops below VR 1 =3.7 volts, the output of comparator  306  is driven low, which deactivates transistor  310  and activates inverter  304 . In this mode, GD circuit generates Vd=2Vb−2Vf. (herein Vf is a PN junction diode  205 ,  207  forwarding voltage of ˜0.7V)  FIG. 4B  graphically illustrates the relationship between Vd and Vb. This figure shows the transition of Vd at Vb=3.7 volts. 
         [0033]      FIG. 5A  illustrates yet another GD circuit  502  that could be employed in the BCM  102  of  FIG. 1 . GD circuit  502  employs a negative feedback loop that includes operational amplifier (opamp)  504 . A negative input to opamp  504  is coupled between resistors  506  and  508 , which in turn is coupled to output node d. A positive input to opamp  504  is coupled to a reference voltage VR 2 . Opamp  504  has a large open loop voltage gain, and as a result the voltage at the positive and negative inputs will be essentially the same. With VR 2 =1 volt, GD circuit  502  may generate Vd=1+R 2 /R 1 , where R 2  is the resistance of resistor  508  and R 1  is the resistance of resistor R 1 . R 1  and R 2  should be large to reduce current flow through resistors  506  and  508 . With R 2 =500 k ohms and R 1 =100 k ohms, GD circuit  502  generates Vd=6 volts when Vb varies between 2.5 volts and 4.2 volts. The output of opamp  504  is also coupled to inverters  512  and  514  so that their outputs vary between ground and Va, the output voltage of opamp  504 , which in turn can vary between ground and Vb. If Vb drops below a certain voltage (e.g., 2.2 volts), GD circuit  502  may generate Vd=Vb−2Vf+2Va. Since the outputs of inventors  512  and  514  can be as high as Va, which can be as high as Vb, Vd=3Vb−2Vf. BMC circuit  102 , however, should prevent Vb from dropping below 2.5 volts. As such, GD circuit  502  will generate Vd=1+R 2 /R 1 =6 volts, assuming R 2 =500 k ohms and R 1 =100 k ohms.  FIG. 5B  graphically illustrates the relationship between Vd and Vb for the voltage range 2.5 volts-4.2 volts. While GD circuit  502  generates a stable Vd that does not exceed the breakdown voltage of BMC circuit  102 , the feedback loop may consume a relatively large amount of power. 
         [0034]      FIG. 6A  illustrates another GD circuit  602  that could be employed in BMC  102 . GD circuit  602  includes a negative feedback loop like the negative feedback loop of GD  502 . GD circuit  602  can also operate in one of two modes, one of which limits the power consumed by the feedback loop. GD circuit  602  includes a comparator circuit  604 , which like the comparator circuit  306  of GD circuit  402 , compares Vb to reference voltage VR 1 , which in this example is set to 3.7 volts. When Vb exceeds VR 1 =3.7 volts, the output of comparator  604  is driven high, which deactivates p-channel metal oxide field effect transistor  608 , inverter  612 , and opamp  610 . In this mode of operation, Schottky diode  614  biases output d to Vb. When Vb drops below reference voltage VR 1 =3.7 volts, the output comparator  604  is driven low, which in turn activates transistor  608 , opamp  610 , and inverter  612 . In this mode, GD circuit  602  generates Vd=1+R 2 /R 1 .  FIG. 6B  graphically illustrates the relationship between Vd and Vb for the voltage range 2.5 volts-4.2 volts. As shown, Vd=Vb until Vb drops below VR 1 =3.7 volts, at which point GD circuit  602  generates Vd=6 volts assuming R 2 =500 k ohms and R 1 =100 k ohms. Advantageously, GD circuit  602  consumes less power when the magnitude of Vb exceeds reference voltage VR 1 , but nonetheless Vd is sufficiently high enough to reduce Rdson of transistor  110 . 
         [0035]      FIG. 7A  illustrates another GD circuit  702  that can be employed in the GD  102 . GD circuit  702  includes a microcontroller unit (MCU)  704  or similar device that can selectively activate or deactivate the combination of transistor  608 , inverter  612 , and opamp  610 . GD circuit  702  also includes a pair of analog to digital (A/D) converters  706  and  708 , which respectively sample analog voltages Vb and Vsense, the voltage generated across sense resistor  106 , which is proportional to current Idischarge flowing therethrough. A/D convertors  706  and  708  generate digital equivalents of the sampled voltages, which are subsequently provided to and processed by MCU  704  in accordance with instructions stored in memory. 
         [0036]    MCU  704  monitors the digital equivalent of Vb and the digital equivalent of Vsense. When Vb is larger than, for example, 3.7 volts, MCU  704  will deactivate transistor  608 , opamp  610 , and inverter  612 . In this mode of operation, GD circuit  702  will generate Vd=Vb−Vf, unless the digital equivalent of Vsense exceeds a predetermined value stored in memory  710 . This may happen, for example, when the mobile device (e.g., a smart phone) enters into a data transmission mode in which it may be important for battery  100  to provide stable output power. A more stable output power can be facilitated by reducing Rdson of transistor  110 . When Vsense exceeds the predetermined value, MCU  704  will activate transistor  608 , opamp  610  and inverter  612 . In this configuration, GD circuit  602  generates Vd=1+R 2 /R 1  at output d. If, however, at any point Vb drops below the threshold voltage of 3.7 volts, MCU  704  will activate transistor  608 , opamp  610 , and inverter  612  so that the output voltage Vd is maintained at 1+R 2 /R 1 .  FIG. 7B  graphically illustrates the relationship between Vd and Idischarge for Vb=2.5 volts and Vb=4.2 volts. 
         [0037]      FIG. 8A  illustrates yet another GD circuit  802  that can be employed in GD circuit  102 . GD circuit  802  includes many of the components shown within the GD circuits  602  and/or  702 . A few significant differences exist. For example, the GD circuit  802  lacks a component such as MCU  704  for controlling opamp  610  and inverter  806 . Rather, these components and switch  804  are controlled by an external signal CP. Many mobile devices that employ rechargeable battery packs, such as the rechargeable battery pack  100  shown in  FIG. 1 , can operate in a stand-by mode in order to conserve the battery pack&#39;s charge. In the normal mode of operation, a mobile device may require substantial discharge current from the battery pack. To accommodate this requirement, CP can be driven high, which in turn closes switch  804  and activates opamp  610  and inverter  806 . In this mold GD control circuit  802  generates Vd=1+R 2 /R 1 . With R 2 =500 k ohms and R 1 =100 k ohms, GD circuit  502  will generate Vd=6 volts, which in turn reduces Rdson of transistor  110 . CP can be driven low when the mobile device is, for example, operating in a standby mode during which less power is needed from battery  104 . With CP set to low, switch  804  is opened, and inverter  806  and opamp  808  are disabled. In this configuration, GD circuit  802  generates Vd=Vb−Vf.  FIG. 8B  graphically illustrates the relationship between Vd and Vb for the voltage range Vb=2.5 volts−Vb=4.2 volts and with CP set to high and low. 
         [0038]    Although the present invention has been described in connection with several embodiments, the invention is not intended to be limited to the specific forms set forth herein. On the contrary, it is intended to cover such alternatives, modifications, and equivalents as can be reasonably included within the scope of the invention as defined by the appended claims.