I, Walter Kester have personal knowledge of the matters stated
`
`or referenced herein and if called to testify about them, I could
`
`and would be able to do so.
`
`1.
`
`I am currently an employee of Analog Devices, Inc. and
`
`am an author of ’’Practical Design Techniques for Power
`
`and Thermal Management” (1998), including Section 5
`
`"Battery Chargers" (Battery Chargers Reference”).
`
`2. As part of my responsibilitiesat Analog Devices, I am
`
`familiar with how this document was prepared and
`
`published.
`
`3. Attached as Exhibit A is a true and correct copy of the
`
`Battery Chargers Reference.
`
`4. Based on my experience with Analog Devices, my
`
`personal knowledge and the records I have reviewed,
`
`the Battery Chargers Reference was printed and publicly
`
`available at ieast as of 1998. I retrieved a copy of the
`
`Battery Chargers Reference attached as Exhibit A from
`
`our publicly available FTP site
`
`(ft
`
`:
`
`ft
`
`.analo .com ub cftl AD|%20Classics Power%
`
`20and%20Thermal%2OIVlanagement,%201998[) on
`
`December 8, 2014, which was maintained by Analog
`
`Devices in the ordinary course of its regularly conducted
`
`activities.
`
`Samsung Exhibit 1039
`
`Samsung v. Affinity
`IPR2014-01181
`
`Page 00001
`
`Samsung Exhibit 1039
`Samsung v. Affinity
`IPR2014-01181
`Page 00001
`
`

`
`Page 00002
`
`

`
`BATTERY CHARGERS
`
`SECTION 5
`BATTERY CHARGERS
`Walt Kester, Joe Buxton
`
`INTRODUCTION
`
`Rechargeable batteries are vital to portable electronic equipment such as laptop
`computers and cell phones. Fast charging circuits must be carefully designed and
`are highly dependent on the particular battery's chemistry. The most popular types
`of rechargeable batteries in use today are the Sealed-Lead-Acid (SLA), Nickel-
`Cadmium (NiCd), Nickel-Metal-Hydride (NiMH), and Lithium-Ion (Li-Ion). Li-Ion is
`fast becoming the chemistry of choice for many portable applications because it
`offers a high capacity-to-size (weight) ratio and a low self-discharge characteristic.
`
`RECHARGEABLE BATTERY
`CONSIDERATIONS IN PORTABLE EQUIPMENT
`
`n Amp-Hour Capacity (C) and Cell Voltage
`n Multiple Cell Configurations: Series/Parallel
`Combinations, Matching Requirements
`n Weight and Volume
`n Cost of Battery Pack
`n Battery Chemistry
`u Sealed Lead Acid (SLA)
`u Nickel-Cadmium (NiCd)
`u Nickel-Metal Hydride (NiMH)
`u Lithium-Ion (Li-Ion)
`u Lithium-Metal (Relatively New)
`n Discharge Characteristics
`n Charge Characteristics
`n Cost and Complexity of "Fast Charging" Circuits
`
`Figure 5.1
`
`There are an enormous number of tradeoffs to be made in selecting the battery and
`designing the appropriate charging circuits. Weight, capacity, and cost are the
`primary considerations in most portable electronic equipment. Unfortunately, these
`considerations are not only interacting but often conflicting. While slow-charging
`(charging time greater than 12 hours) circuits are relatively simple, fast-charging
`circuits must be tailored to the battery chemistry and provide both reliable charging
`and charge termination. Overcharging batteries can cause reduced battery life,
`overheating, the emission of dangerous corrosive gasses, and sometimes total
`destruction. For this reason, fast-charging circuits generally have built-in backup
`means to terminate the charge should the primary termination method fail.
`
`5.1
`
`Page 00003
`
`

`
`BATTERY CHARGERS
`
`Understanding battery charger electronics requires a knowledge of the battery
`charge and discharge characteristics as well as charge termination techniques.
`
`BATTERY FUNDAMENTALS
`
`Battery capacity, C, is expressed in Amp hours, or mA hours and is a figure of merit
`of battery life between charges. Battery current is described in units of C-Rate. For
`instance, a 1000mA-h battery has a C-Rate of 1000mA. The current corresponding
`to 1C is 1000mA, and for 0.1C, 100mA. For a given cell type, the behavior of cells
`with varying capacity is similar at the same C-Rate.
`
`"C-RATE" DEFINITION
`
`n Battery Charge and Discharge Currents are Expressed
`(Normalized) in Terms of "C-Rate"
`n C-Rate = C / 1 hour, Where C is the Battery Capacity
`Expressed in A-hour, or mA-hour
`
`n Example:
`u A 1000 mA-h Battery has a "C-Rate" of 1000mA
`u The Current Corresponding to 1C is 1000mA
`u The Current Corresponding to 0.1C is 100mA
`u The Current Corresponding to 2C is 2000mA
`
`n For a Given Cell Type, the Behavior of Cells with
`Varying Capacity is Similar at the same C-rate
`
`Figure 5.2
`
`There are a number of other figures of merit used to characterize batteries which
`are summarized in Figure 5.3. These figures of merit are used to characterize
`various battery chemistries as shown in Figure 5.4. Note that in Figure 5.4, the
`approximate chronology of battery technology is from left to right.
`
`A few terms relating to batteries deserve further clarification. Self-discharge is the
`rate at which a battery discharges with no load. Li-Ion batteries are a factor of two
`better than NiCd or NiMH in this regard. The discharge rate is the maximum
`allowable load or discharge current, expressed in units of C-Rate. Note that all
`chemistries can be discharged at currents higher than the battery C-Rate. The
`number of charge and discharge cycles is the average number of times a battery can
`be discharged and then recharged and is a measure of the battery's service life.
`
`5.2
`
`Page 00004
`
`

`
`BATTERY CHARGERS
`
`RECHARGEABLE BATTERY
`FIGURES OF MERIT
`
`n Cell Voltage
`n Capacity: C, Measured in Amp-hours (A-h) or mA-hours (mA-h)
`n Energy Density (Volume): Measured in Watt-hours/liter (Wh/l)
`n Energy Density (Weight): Measured in Watt-hours/kilogram (Wh/kg)
`n Cost: Measured in $/Wh
`n Memory Effect?
`n Self-Discharge Rate: Measured in %/month, or %/day
`n Operating Temperature Range
`n Environmental Concerns
`
`Figure 5.3
`
`RECHARGEABLE BATTERY TECHNOLOGIES
`
`Sealed
`Lead-
`Acid
`2
`
`35
`
`85
`
`Nickel
`Cadmium*
`
`1.20
`
`45
`
`150
`
`Nickel
`Metal
`Hydride*
`1.25
`
`55
`
`180
`
`Lithium
`Ion*
`
`Lithium
`Metal*
`
`3.6
`
`100
`
`225
`
`3.0
`
`140
`
`300
`
`Average Cell Voltage (V)
`
`Energy Density (Wh/kg)
`
`Energy Density (Wh/l)
`
`Cost ($/Wh)
`
`0.25 - 0.50
`
`0.75 - 1.5
`
`1.5 - 3.0
`
`2.5 - 3.5
`
`1.4 - 3.0
`
`Memory Effect?
`
`No
`
`Self-Discharge (%/month)
`
`5 - 10
`
`Discharge Rate
`
`Charge/Discharge Cycles
`
`<5C
`
`500
`
`Yes
`
`25
`
`>10C
`
`1000
`
`No
`
`20 - 25
`
`<3C
`
`800
`
`No
`
`8
`
`<2C
`
`1000
`
`No
`
`1 - 2
`
`<2C
`
`1000
`
`Temperature Range ( ºC)
`
`0 to +50
`
`–10 to +50 –10 to +50 –10 to +50 –30 to +55
`
`Environmental Concerns
`
`Yes
`
`Yes
`
`No
`
`No
`
`No
`
`* Based on AA-Size Cell
`
`Figure 5.4
`
`5.3
`
`Page 00005
`
`

`
`BATTERY CHARGERS
`
`Memory occurs only in NiCd batteries and is relatively rare. It can occur during
`cyclic discharging to a definite fixed level and subsequent recharging. Upon
`discharging, the cell potential drops several tenths of a volt below normal and
`remains there for the rest of the discharge. The total ampere-hour capacity of the
`cell is not significantly affected. Memory usually disappears if the cell is almost fully
`discharged and then recharged a time or two. In practical applications, memory is
`not often a problem because NiCd battery packs are rarely discharged to the same
`level before recharging.
`
`Environmental concerns exist regarding the proper disposal of sealed-lead-acid and
`NiCd batteries because of hazardous metal content. NiMH and Li-Ion batteries do
`not contain significant amounts of pollutant, but nevertheless, some caution should
`be used in their disposal.
`
`The discharge profiles of these four popular type of batteries are shown in Figure
`5.5. A discharge current of 0.2C was used in each case. Note that NiCd, NiMH, and
`SLA batteries have a relatively flat profile, while Li-Ion batteries have a nearly
`linear discharge profile.
`
`BATTERY DISCHARGE PROFILES AT 0.2C RATE
`5
`
`Li-Ion
`
`SLA
`
`NiCd and NiMH
`
`0
`
`1
`
`4
`3
`2
`DISCHARGE TIME - HOURS
`
`5
`
`Figure 5.5
`
`TERMINAL
`VOLTAGE-
`V
`
`4
`
`3
`
`2
`
`1
`
`0
`
`5.4
`
`Page 00006
`
`

`
`BATTERY CHARGERS
`
`BATTERY CHARGING
`
`A generalized battery charging circuit is shown in Figure 5.6. The battery is charged
`with a constant current until fully charged. The voltage developed across the
`RSENSE resistor is used to maintain the constant current. The voltage is
`continuously monitored, and the entire operation is under the control of a
`microcontroller which may even have an on-chip A/D converter. Temperature
`sensors are used to monitor battery temperature and sometimes ambient
`temperature.
`
`GENERALIZED BATTERY CHARGING CIRCUIT
`
`CHARGING CURRENT CONTROL
`
`RSENSE
`
`CURRENT
`SENSE
`
`TEMP
`SENSOR
`
`TEMP
`SENSOR
`
`+
`
`BATTERY
`
`VOLTAGE
`SENSOR
`
`CONTROL
`CIRCUITS
`AND µC
`
`AMBIENT
`TEMP
`
`BATTERY
`TEMP
`
`Figure 5.6
`
`This type of circuit represents a high level of sophistication and is primarily used in
`fast-charging applications, where the charge time is less than 3 hours. Voltage and
`sometimes temperature monitoring is required to accurately determine the state of
`the battery and the end-of-charge. Slow charging (charge time greater than 12
`hours) requires much less sophistication and can be accomplished using a simple
`current source. Typical characteristics for slow charging are shown in Figure 5.7.
`Charge termination is not critical, but a timer is sometimes used to end the slow
`charging of NiMH batteries. If no charge termination is indicated in the table, then
`it is safe to trickle charge the battery at the slow-charging current for indefinite
`periods of time. Trickle charge is the charging current a cell can accept continually
`without affecting its service life. A safe trickle charge current for NiMH batteries is
`typically 0.03C. For example, for an NiMH battery with C = 1A-hr, 30mA would be
`safe. Battery manufacturers can recommend safe trickle charge current limits for
`specific battery types and sizes.
`
`5.5
`
`Page 00007
`
`

`
`BATTERY CHARGERS
`
`BATTERY CHARGING CHARACTERISTICS
`FOR SLOW CHARGING
`
`Current
`
`SLA
`
`0.25C
`
`Voltage (V/cell)
`
`2.27
`
`NiCd
`
`0.1C
`
`1.50
`
`NiMH
`
`0.1C
`
`1.50
`
`Time (hr)
`
`24
`
`16
`
`16
`
`Li-Ion
`
`0.1C
`
`4.1 or
`4.2
`
`16
`
`Temp. Range
`
`0º/45ºC
`
`5º/45ºC
`
`5º/40ºC
`
`5º/40ºC
`
`Termination
`
`None
`
`None
`
`Timer
`
`Voltage Limit
`
`Figure 5.7
`
`Fast-charging batteries (charge time less than 3 hours) requires much more
`sophisticated techniques. Figure 5.8 summarizes fast-charging characteristics for
`the four popular battery types. The most difficult part of the process is to correctly
`determine when to terminate the charging. Undercharged batteries have reduced
`capacity, while overcharging can damage the battery, cause catastrophic outgassing
`of the electrolyte, and even explode the battery.
`
`BATTERY CHARACTERISTICS
`FOR FAST CHARGING (<3HOURS)
`SLA
`NiCd
`NiMH
`
`Current
`
`Voltage (V/cell)
`
`Time (hours)
`
`Temp. Range (ºC)
`
`Primary
`Termination
`
`Secondary
`Termination
`
`‡‡ 1.5C
`2.45
`
`££ 1.5
`0 to 30
`
`Imin,
`TCO
`DD
`Timer,
`TCO
`DD
`
`‡‡ 1C
`1.50
`
`3
`
`££
`
`15 to 40
`
`–DD V,
`dT/dt
`
`TCO,
`Timer
`
`1C
`
`‡‡
`
`1.50
`
`££ 3
`15 to 40
`
`dT/dt,
`dV/dt = 0
`
`TCO,
`Timer
`
`Li-Ion
`
`1C
`
`4.1 or
` 50mV
`4.2 ––
`2.5
`
`10 to 40
`
`Imin @
`Voltage Limit
`TCO,
`Timer
`
`C = Normal Capacity, Imin = Minimum Current-Threshold Termination
`TCO = Absolute Temperature Cutoff, DDTCO = Temperature Rise Above Ambient
`Figure 5.8
`
`5.6
`
`Page 00008
`
`

`
`BATTERY CHARGERS
`
`Because of the importance of proper charge termination, a primary and secondary
`method is generally used. Depending on the battery type, the charge may be
`terminated based on monitoring battery voltage, voltage change vs. time,
`temperature change, temperature change vs. time, minimum current at full voltage,
`charge time, or various combinations of the above.
`
`Battery voltage and temperature are the most popular methods of terminating the
`charge of NiCd and NiMH batteries. Figure 5.9 shows the cell voltage and
`temperature as a function of charge time for these two types of batteries (charging
`at the 1C-rate). Note that NiCd has a distinct peak in the cell voltage immediately
`preceding full charge. NiMH has a much less pronounced peak, as shown in the
`dotted portion of the curve. A popular method of charge termination for NiCd is the
`–DV method, where the charge is terminated after the cell voltage falls 10 to 20mV
`after reaching its peak.
`
`Note that for both types the temperature increases rather suddenly near full
`charge. Because of the much less pronounced voltage peak in the NiMH
`characteristic, the change in temperature with respect to time (dT/dt) is most often
`used as a primary charge termination method.
`
`NiCd/NiMH BATTERY TEMPERATURE AND VOLTAGE
`CHARGING CHARACTERISTICS
`
`dV/dt = 0
`
`NiMH
`
`Fail Safe
`TCO
`
`CELL
`V
`
`CELL
`T
`
`CELL VOLTAGE
`
`CELL TEMP
`
`–DDV
`(NiCd)
`
`dT/dt Threshold
`
`Approx. Time to full charge
`
`Fail Safe Charge Time
`
`TIME
`
`Figure 5.9
`
`In addition to the primary termination, secondary terminations are used as backups
`for added protection. The primary and secondary termination methods for NiCd and
`NiMH cells are summarized in Figure 5.10. All these termination methods are
`generally controlled by a microcontroller. After proper signal conditioning, the cell
`
`5.7
`
`Page 00009
`
`

`
`BATTERY CHARGERS
`
`voltage and temperature are converted into digital format using 8 or 10-bit A/D
`converters which may be located inside the microcontroller itself.
`
`NiCd AND NiMH FAST CHARGE TERMINATION
`METHODS SUMMARY
`
`NiCd
`
`NiMH
`
`n Primary:
`u –DD V
`u dT/dt Threshold
`
`n Primary:
`u dT/dt Threshold
`u Zero dV/dt
`
`n Secondary:
`u TCO (Absolute
`Temperature Cutoff)
`u Timer
`
`n Secondary:
`u TCO (Absolute
`Temperature Cutoff)
`u Timer
`
`Figure 5.10
`
`Li-Ion cells behave quite differently from the other chemistries in that there is a
`gradual rise to the final cell voltage when charged from a constant current source
`(see Figure 5.11). The ideal charging source for Li-Ion is a current-limited constant
`voltage source (sometimes called constant-current, constant-voltage, or CC-CV). A
`constant current is applied to the cell until the cell voltage reaches the final battery
`voltage (4.2V –50mV for most Li-Ion cells, but a few manufacturers' cells reach full
`charge at 4.1V). At this point, the charger switches from constant-current to
`constant-voltage, and the charge current gradually drops. The gradual drop in
`charge current is due to the internal cell resistance. Charge is terminated when the
`current falls below a specified minimum value, IMIN. It should be noted that
`approximately 65% of the total charge is delivered to the battery during the
`constant current mode, and the final 35% during the constant voltage mode.
`
`Secondary charge termination is usually handled with a timer or if the cell
`temperature exceeds a maximum value, TCO (absolute temperature cutoff).
`
`It should be emphasized that Li-Ion batteries are extremely sensitive to overcharge!
`Even slight overcharging can result in a dangerous explosion or severely decrease
`battery life. For this reason, it is critical that the final charge voltage be controlled
`to within about –50mV of the nominal 4.2V value.
`
`5.8
`
`Page 00010
`
`

`
`Li-Ion FAST CHARGING CHARACTERISTICS
`
`BATTERY CHARGERS
`
`CELL
`VOLTAGE
`(V)
`
`4.3
`
`4.2
`
`4.1
`
`4.0
`
`3.9
`
`3.8
`
`3.7
`
` 3.6
`
`0
`
`CELL
`VOLTAGE
`
`CELL
`CURRENT
`
`1.0
`
`2.0
`
`CHARGE TIME (HOURS)
`
`Figure 5.11
`
`1C
`
`CELL
`CURRENT
`(C)
`
`IMIN
`
`0
`
`3.0
`
`Battery packs which contain multiple Li-Ion cells are generally manufactured with
`matched cells and voltage equalizers. The external charging circuitry controls the
`charging current and monitors the voltage across the entire battery pack. However,
`the voltage across each cell is also monitored within the pack, and cells which have
`higher voltage than others are discharged through shunt FETs. If the voltage across
`any cell exceeds 4.2V, charging must be terminated.
`
`Li-Ion CHARGE TERMINATION TECHNIQUES
`
`n Primary:
`u Detection of Minimum Threshold Charging Current
`with Cell Voltage Limited to 4.2V
`
`n Secondary:
`u TCO (Absolute Temperature Cutoff)
`u Timer
`
`n Accurate Control (± 50mV) of Final Battery Voltage
`Required for Safety!
`
`n Multiple-Cell Li-Ion Battery Packs Require Accurate Cell
`Matching and/or Individual Cell Monitors and Charge
`Current Shunts for Safety
`
`Figure 5.12
`
`5.9
`
`Page 00011
`
`

`
`BATTERY CHARGERS
`
`Under no circumstances should a multiple-cell Li-Ion battery pack be constructed
`from individual cells without providing this voltage equalization function!
`
`While the dangers of overcharging cannot be overstated, undercharging a Li-Ion cell
`can greatly reduce capacity as shown in Figure 5.13. Notice that if the battery is
`undercharged by only 100mV, 10% of the battery capacity is lost. For this reason,
`accurate control of the final charging voltage is mandatory in Li-Ion chargers.
`
`EFFECT OF UNDERCHARGE ON Li-Ion
`BATTERY CAPACITY
`
`CAPACITY
`(%)
`
`100
`
`98
`
`96
`
`94
`
`92
`
`90
`
`4.100
`
`4.125
`
`4.150
`
`4.175
`
`4.200
`
`FINAL BATTERY VOLTAGE (V)
`
`Figure 5.13
`
`From the above discussion, it is clear that accurate control of battery voltage and
`current is key to proper charging, regardless of cell chemistry. The ADP3810/3811-
`series of ICs makes this job much easier to implement. A block diagram of the IC is
`shown in Figure 5.14. Because the final voltage is critical in charging Li-Ion cells,
`the ADP3810 has precision resistors (R1 and R2) which are accurately trimmed for
`the standard Li-Ion cell/multiple cell voltages of 4.2V (1 cell), 8.4V (2 cells), 12.6V (3
`cells), and 16.8V (4 cells). The value of the charging current is controlled by the
`voltage applied to the VCTRL input pin. The charging current is constantly
`monitored by the voltage at the VCS input pin. The voltage is derived from a low-
`side sense resistor placed in series with the battery. The output of the ADP3810
`(OUT pin) is applied to external circuitry, such as a PWM, which controls the actual
`charging current to the battery. The output is a current ranging from 0 to 5mA
`which is suitable for driving an opto-isolator in an isolated system.
`
`5.10
`
`Page 00012
`
`

`
`BATTERY CHARGERS
`
`ADP3810/3811 BLOCK DIAGRAM
`
`GND
`
`VCS
`
`VCC
`
`VREF VSENSE
`
`VREF
`
`1.5MWW
`
`80kWW
`
`UVLO
`
`+ -
`
`VCTRL
`
`*ADP3810
`ONLY
`R1*
`R2*
`
`+
`
`-
`
`UVLO
`
`VREF
`
`+
`
`-
`
`2V
`
`-
`
`+
`
`-
`
`+
`
`-
`
`+
`
`UVLO
`
`GM1
`
`GM2
`
`OUT
`
`GM
`
`COMP
`
`OVERVOLTAGE LOCKOUT
`
`ADP3810 / ADP3811
`
`Figure 5.14
`
`ADP3810/3811 BATTERY CHARGER
`CONTROLLER KEY FEATURES
`
` 1%, ADP3810
`
`n Programmable Charge Current
`n Battery Voltage Limits
`u (4.2V, 8.4V, 12.6V, 16.8V) ––
`u Adjustable, ADP3811
`n Overvoltage Comparator (6% Over Final Voltage)
`n Input Supply Voltage Range 2.7V to 16V
`n Undervoltage Shutdown for VCC less than 2.7V
`n Sharp Current to Voltage Control Transition Due to
`High Gain GM Stages
`n SO-8 Package with Single Pin Compensation
`
`Figure 5.15
`
`5.11
`
`Page 00013
`
`

`
`BATTERY CHARGERS
`
`The charging current is held constant until the battery voltage (measured at the
`VSENSE input) reaches the specified value (i.e. 4.2V per cell). The voltage control
`loop has an accuracy of –1%, required by Li-Ion batteries. At this point, the control
`switches from the current control loop (VCS) to the voltage control loop (VSENSE),
`and the battery is charged with a constant voltage until charging is complete. In
`addition, the ADP3810 has an overvoltage comparator which stops the charging
`process if the battery voltage exceeds 6% of its programmed value. This function
`protects the circuitry should the battery be removed during charging. In addition, if
`the supply voltage drops below 2.7V, the charging is stopped by the undervoltage
`lockout (UVLO) circuit.
`
`The ADP3811 is identical to the ADP3810 except that the VSENSE input ties
`directly to the GM2 stage input, and R1/R2 are external, allowing other voltages to
`be programmed by the user for battery chemistries other than Li-Ion.
`
`A simplified functional diagram of a battery charger based on the ADP3810/3811
`battery charger controller is shown in Figure 5.16. The ADP3810/3811 controls the
`DC-DC converter which can be one of many different types such as a buck, flyback,
`or linear regulator. The ADP3810/3811 maintains accurate control of the current
`and voltage loops.
`
`ADP3810/3811 SIMPLIFIED BATTERY CHARGER
`
`VIN
`
`IN
`
`OUT
`
`DC/DC
`CONVERTER
`
`CTRL
`
`GND
`
`VIN RETURN
`
`VOLTAGE
`LOOP
`
`ICHARGE
`
`+
`
`VBAT
`
`CURRENT
`LOOP
`
`RCS
`
`CC
`
`IOUT
`
`RC
`
`R3
`
`R1*
`R2*
`
`COMP
`
`VCC
`
`VCS
`
`VSENSE
`
`OUT
`
`ADP3810/3811
`
`VCTRL
`
`*INTERNAL
`FOR ADP3810
`
`CHARGE
`CURRENT
`CONTROL
`CIRCUITS
`
`GND
`
`Figure 5.16
`
`5.12
`
`Page 00014
`
`

`
`BATTERY CHARGERS
`
`The value of the charge current is controlled by the feedback loop comprised of RCS,
`R3, GM1, the external DC-DC converter, and the DC voltage at the VCTRL input.
`The actual charge current is set by the voltage, VCTRL, and is dependent upon the
`choice for the values of RCS and R3 according to:
`
`1
`ICHARGE RCS
`=
`
`
`R3
`(cid:215) (cid:215)
`
`k80 W
`
`VCTRL
`
`.
`
`Typical values are RCS = 0.25W and R3 = 20kW, which result in a charge current of
`1.0A for a control voltage of 1.0V. The 80kW resistor is internal to the IC, and it is
`trimmed to its absolute value. The positive input of GM1 is referenced to ground,
`forcing the VCS point to a virtual ground.
`
`The low-side sense resistor, RCS, converts the charging current into a voltage which
`is applied to the VCS pin. If the charge current increases above its programmed
`value, the GM1 stage forces the current, IOUT, to increase. The higher IOUT
`decreases the duty cycle of the DC-DC converter, reducing the charging current and
`balancing the feedback loop.
`
`As the battery approaches its final charge voltage, the voltage control loop takes
`over. The system becomes a voltage source, floating the battery at constant voltage,
`thereby preventing overcharging. The voltage control loop is comprised of R1, R2,
`GM2, and the DC-DC converter. The final battery voltage is simply set by the ratio
`of R1 to R2 according to:
`
`1
`
`.
`
`1 2
`R R
`
`VBAT
`
`=
`
`
`
`2 000.
`
`V
`
`(cid:230)Ł(cid:231) (cid:246)ł(cid:247)
`+
`If the battery voltage rises above its programmed voltage, VSENSE is pulled high
`causing GM2 to source more current, thereby increasing IOUT. As with the current
`loop, the higher IOUT reduces the duty cycle of the DC-DC converter and causes the
`battery voltage to fall, balancing the feedback loop.
`
`Notice that because of the low-side sensing scheme, the ground of the circuits in the
`system must be isolated from the ground of the DC-DC converter.
`
`Further design details for specific applications are given in the ADP3810/3811 data
`sheet (Reference 7), including detailed analysis and computations for compensating
`the feedback loops with resistor RC and capacitor CC.
`
`The ADP3810/3811 does not include circuitry to detect charge termination criteria
`such as –DV or dT/dt, which are common for NiCd and NiMH batteries. If such
`charge termination schemes are required, a low cost microcontroller can be added to
`the system to monitor the battery voltage and temperature. A PWM output from the
`microcontroller can subsequently program the VCTRL input to set the charge
`current. The high impedance of VCTRL enables the addition of an RC filter to
`integrate the PWM output into a DC control voltage.
`
`5.13
`
`Page 00015
`
`(cid:215)
`

`
`BATTERY CHARGERS
`
`OFF-LINE, ISOLATED, FLYBACK BATTERY CHARGER
`
`The ADP3810/3811 are ideal for use in isolated off-line chargers. Because the output
`stage can directly drive an optocoupler, feedback of the control signal across an
`isolation barrier is a simple task. Figure 5.17 shows a simplified schematic of a
`flyback battery charger with isolation provided by the flyback transformer and the
`optocoupler. For details of the schematic, refer to the ADP3810/3811 data sheet
`(Reference 7).
`
`Caution: This circuit contains lethal AC and DC voltages, and appropriate
`precautions must be observed!! Please refer to the data sheet text and schematic if
`building this circuit!!
`
`The operation of the circuit is similar to that of Figure 5.16. The DC-DC converter
`block is comprised of a primary-side PWM circuit and flyback transformer, and the
`control signal passes through the optocoupler to the PWM.
`
`120 -
`220V
`
`AC
`**
`
`ADP3810 OFF-LINE FLYBACK BATTERY CHARGER
`FOR TWO Li-Ion CELLS (SIMPLIFIED SCHEMATIC!!)
`**
`**
`
`RECTIFIER
`AND FILTER
`
`170 - 340V DC
`
`3.3V
`
`ICHARGE
`
`VBAT = 8.4V
`+
`
`RCS
`
`0.25WW
`
`20kWW
`
`100kWW
`
`13V
`
`COMP
`
`VCC
`
`PWM
`3845
`
`VFB
`
`OUT
`
`ISENSE
`
`VREF
`
`RLIM
`
`OPTO
`ISOLATOR
`
`VCS
`
`VCC
`
`VSENSE
`
`OUT
`
`ADP3810-8.4
`
`VCTRL
`
`COMP
`
`GND
`
`CHARGE
`CURRENT
`VOLTAGE
`CONTROL
`
`**
`
`WARNING: LETHAL
`VOLTAGES PRESENT,
`USE EXTREME CAUTION!
`
`Figure 5.17
`
`A typical current-mode flyback PWM controller (3845-series) was chosen for the
`primary control for several reasons. First and most importantly, it is capable of
`operating from very small duty cycles to near the maximum desired duty cycle. This
`makes it a good choice for a wide input AC supply voltage variation requirement,
`which is usually between 70V and 270V for world-wide applications. Add to that the
`additional requirement of 0% to 100% current control, and the PWM duty cycle must
`
`5.14
`
`Page 00016
`
`

`
`BATTERY CHARGERS
`
`have a wide range. This charger achieves these ranges while maintaining stable
`feedback loops.
`
`The detailed operation and design of the primary side PWM is widely described in
`the technical literature and is not detailed here. However, the following explanation
`should make clear the reasons for the primary-side component choices. The PWM
`frequency is set to around 100kHz as a reasonable compromise between inductive
`and capacitive component sizes, switching losses, and cost.
`
`The primary-side PWM-IC derives its starting VCC through a 100kW resistor
`directly from the rectified AC input. After start-up, a simple rectifier circuit driven
`from a third winding on the transformer charges a 13V zener diode which supplies
`the VCC to the 3845 PWM.
`
`While the signal from the ADP3810/3811 controls the average charge current, the
`primary side should have cycle by cycle limit of the switching current. This current
`limit has to be designed so that, with a failed or malfunctioning secondary circuit or
`optocoupler, the primary power circuit components (the MOSFET and the
`transformer) won't be overstressed. In addition, during start-up or for a shorted
`battery, VCC to the ADP3810/3811 will not be present. Thus, the primary side
`current limit is the only control of the charge current. As the secondary side VCC
`rises above 2.7V, the ADP3810/3811 takes over and controls the average current.
`The primary side current limit is set by the RLIM resistor.
`
`The current drive of the ADP3810/3811's output stage directly connects to the
`photodiode of an optocoupler with no additional circuitry. With 5mA of output
`current, the output stage can drive a variety of optocouplers.
`
`A current-mode flyback converter topology is used on the secondary side. Only a
`single diode is needed for rectification, and no filter inductor is required. The diode
`also prevents the battery from back driving the charger when input power is
`disconnected. The RCS resistor senses the average current which is controlled via
`the VCS input.
`
`The VCC source to the ADP3810/3811 can come from a direct connection to the
`battery as long as the battery voltage remains below the specified 16V operating
`range. If the battery voltage is less than 2.7V (e.g., with a shorted battery, or a
`battery discharged below its minimum voltage), the ADP3810/3811 will be in
`Undervoltage Lock Out (UVLO) and will not drive the optocoupler. In this condition,
`the primary PWM circuit will run at its designed current limit. The VCC of the
`ADP3810/3811 is boosted using the additional rectifier and 3.3V zener diode. This
`circuit keeps VCC above 2.7V as long as the battery voltage is at least 1.5V with a
`programmed charge current of 0.1A. For higher programmed charge current, the
`battery voltage can drop below 1.5V, and VCC is still maintained above 2.7V.
`
`The charge current versus charge voltage characteristics for three different charge
`current settings are shown in Figure 5.18. The high gain of the internal amplifiers
`ensures the sharp transition between current-mode and voltage-mode regardless of
`the charge current setting. The fact that the current remains at full charging until
`the battery is very close to its final voltage ensures fast charging times. It should be
`noted, however, that the curves shown in Figure 5.18 reflect the performance of only
`
`5.15
`
`Page 00017
`
`

`
`BATTERY CHARGERS
`
`the charging circuitry and not the I/V characteristics when charging an actual
`battery. The internal battery resistance will cause a more gradual decrease in
`charge current when the final cell voltage is reached (see Figure 5.11, for example).
`
`A detailed description of this off-line charging circuit is contained in the
`ADP3810/3811 data sheet (Reference 7) along with design examples for those
`interested.
`
`CHARGE CURRENT VS. VOLTAGE FOR FLYBACK
`CHARGER (2 IDEAL Li-Ion CELLS,
`ZERO CELL RESISTANCE)
`
`ILIMIT
`(A)
`
`1.0
`0.9
`0.8
`0.7
`0.6
`0.5
`0.4
`0.3
`0.2
`0.1
`0.0
`
`VCTRL = 1.0V
`
`VCTRL = 0.5V
`
`VCTRL = 0.1V
`
`4.5
`
`5
`
`5.5
`
`6
`
`6.5
`
`7
`
`7.5
`
`8
`
`8.5
`
`VOUT
`
`Figure 5.18
`
`Off-line chargers are often used in laptop computers as shown in Figure 5.19. Here,
`there are many options. The "brick" may consist of a simple AC/DC converter, and
`the charger circuit put inside the laptop. In some laptops, the charger circuit is part
`of the brick. Ultimately, the entire AC/DC converter as well as the charger circuit
`can be put inside the laptop, thereby eliminating the need for the brick entirely.
`There are pros and cons to all the approaches, and laptop computer designers
`wrestle with these tradeoffs for each new design.
`
`5.16
`
`Page 00018
`
`

`
`BATTERY CHARGERS
`
`APPLICATION OF OFF-LINE CHARGER IN
`LAPTOP COMPUTERS
`
`AC/DC,
`MAY INCLUDE
`CHARGER
`
`BRICK OUTSIDE
`
`BRICK INSIDE
`
`Figure 5.19
`
`LINEAR BATTERY CHARGER
`
`In some applications where efficiency and heat generation is not a prime concern, a
`low cost linear battery charger can be an ideal solution. The ADP3820 linear
`regulator controller is designed to accurately charge single cell Li-Ion batteries as
`shown in Figure 5.20. Its output directly controls the gate of an external p-channel
`MOSFET. As the circuit shows, a linear implementation of a battery charger is a
`simple approach. In addition to the IC and the MOSFET, only an external sense
`resistor and input and output capacitors are required. The charge current is set by
`choosing the appropriate value of sense resistor, RS. The ADP3820 includes all the
`components needed to guarantee a system level specification of ±1% final battery
`voltage, and it is available with either a 4.2V or 4.1V final battery voltage. The
`ADP3820 has an internal precision reference, low offset amplifier, and trimmed thin
`film resistor divider to guarantee Li-Ion accuracy. In addition, an enable (EN) pin is
`available to place the part in low current shutdown.
`
`If a linear charger is needed for higher Li-Ion battery voltages such as 8.4V, 12.6V,
`or 16.8V, the ADP3810 with an external MOSFET can also be used. Refer to the
`ADP3810 data sheet for more details.
`
`5.17
`
`Page 00019
`
`

`
`BATTERY CHARGERS
`
`The tradeoff between using a linear regulator as shown versus using a flyback or
`buck-type of charger is efficiency versus simplicity. The linear charger of Figure 5.20
`is very simple, and it uses a minimal amount of external components. However, the
`efficiency is poor, especially when there is a large difference between the input and
`output voltages. The power loss in the power MOSFET is equal to (VIN–
`VBAT)•ICHARGE. Since the circuit is powered from a wall adapter, efficiency may
`not be a big concern, but the heat dissipated in the pass transistor could be
`excessive.
`
`ADP3820 LINEAR REGULATOR CONTROLLER
`FOR Li-Ion BATTERY CHARGING
`RS
`IFR9014
`
`VIN
`
`VBAT
`
`40mWW
`
`+
`
`1µF
`
`IS
`
`G
`
`OUT
`
`ADP3820-4.2
`
`IN
`
`EN
`
`100kWW
`
`GND
`
`+
`
`10µF
`
`Li-Ion
`Battery
`
`n ± 1% Accuracy over –20°C to +85°C
`n 4.2V/4.1V Final Battery Voltage Options
`n Low Quiescent Current, Shutdown Current < 1µA
`n Externally Programmable Current Limit
`
`Figure 5.20
`
`SWITCH MODE DUAL CHARGER FOR LI-ION, NICD, AND
`NIMH BATTERIES
`
`The ADP3801 and ADP3802 are complete battery charging ICs with on-chip buck
`regulator control circuits. The devices combine a high accuracy, final battery voltage
`control with a constant charge current control, and on-chip 3.3V Low Drop-Out
`Regulator. The accuracy of the final battery voltage control is –0.75% to safely
`charge Li-Ion batteries. An internal multiplexer allows the alternate charging of two
`separate battery stacks. The final voltage is pin programmable to one of six options:
`4.2V (one Li-Ion cell), 8.4V (two Li-Ion cells), 12.6V (three Li-Ion cells), 4.5V (three
`NiCd/NiMH cells), 9.0V(six NiCd/NiMH cells), or 13.5V (nine NiCd/NiMH cells). In
`addition, a pin is provided for changing the final battery voltage by up to –10% to
`adjust for variations in battery chemistry from different Li-Ion manufacturers. A
`functional diagram along with a typical application circuit is shown in Figure 5.21.
`
`5.18
`
`Page 00020
`
`

`
`BATTERY CHARGERS
`
`The ADP3801 and ADP3802 directly drive an external PMOS transistor. Switching
`frequencies of the family are 200kHz (ADP3801), and 500kHz (ADP3802). An on-
`chip end of charge comparator indicates when the charging current drops