Secondary Side, Off-Line Battery Charger Controllers ADP3810/ADP3811

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Secondary Side, Off-Line Battery Charger Controllers ADP3810/ADP3811

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FEATURES Programmable Charge Current High Precision Battery Voltage Limit Precision 2.000 Reference Voltage Drop Current Sense: Full Scale Full Operation Shorted Open Battery Conditions Drives Diode-Side Optocoupler Wide Operating Supply Range: Undervoltage Lockout SO-8 Package ADP3810 Internal Precision Voltage Divider Battery Sense Four Final Battery Voltage Options Available: 12.6 16.8 ADP3811 Adjustable Final Battery Voltage APPLICATIONS Battery Charger Controller for: LiIon Batteries (ADP3810) NiCad, NiMH Batteries (ADP3811) GENERAL DESCRIPTION
Secondary Side, Off-Line Battery Charger Controllers ADP3810/ADP3811
off-line applications, output directly drives diode side optocoupler give isolated feedback control primary side PWM. circuitry includes gain (gm) stages, precision reference, control input buffer, Undervoltage Lock (UVLO) comparator, output buffer overvoltage comparator. current limit amplifier senses voltage drop across external sense resistor control average current charging battery. voltage drop adjusted from giving charging current limit from amps with 0.25 sense resistor. external voltage VCTRL input sets voltage drop. Because this input high impedance, filtered output used voltage. battery voltage approaches voltage limit, voltage sense amplifier takes over maintain constant battery voltage. amplifiers essentially operate "OR" fashion. Either current limited, voltage limited. ADP3810 internal thin-film resistors that trimmed provide precise final voltage LiIon batteries. Four voltage options available, corresponding LiIon cells follows: 12.6 16.8 ADP3811 omits these resistors allowing battery voltage programmed with external resistors.
ADP3810 ADP3811 combine programmable current limit with battery voltage limit provide constant current, constant voltage battery charger controller. secondary side,
FUNCTIONAL BLOCK DIAGRAM
VREF VSENSE
1.5M VREF
UVLO VREF UVLO
ADP3810 ONLY
VCTRL UVLO
ADP3810/ ADP3811
COMP
REV.
Information furnished Analog Devices believed accurate reliable. However, responsibility assumed Analog Devices use, infringements patents other rights third parties which result from use. license granted implication otherwise under patent patent rights Analog Devices. Technology Way, P.O. 9106, Norwood, 02062-9106, U.S.A. Tel: 617/329-4700 World Wide Site: http://www.analog.com Fax: 617/326-8703 Analog Devices, Inc., 1996
ADP3810/ADP3811-SPECIFICATIONS (-40
10.0 unless otherwise noted)
ADP3810 -300 -285 +1.0 210k 420k 630k 840k Units +1.0 +1.8 +0.25 0.02
Parameter CURRENT SENSE1 Full-Scale Current Sense Voltage Minimum Current Sense Voltage Current Programming Input Range Gain (VOUT/VCS) Control Input Bias Current VOLTAGE SENSE Accuracy2-ADP3810 Input Resistance-ADP3810 Input Resistance-ADP3810 Input Resistance-ADP3810 Input Resistance-ADP3810 Offset Voltage-ADP3811 Bias Current-ADP3811 Gain (VOUT/VSENSE)3 REFERENCE Output Voltage Accuracy ADP3810 ADP3811 Load Regulation Line Regulation Output Voltage Noise Load Current (Sourcing) OUTPUT Output Current Saturation Voltage Gain (VOUT/VCOMP) UNDERVOLTAGE LOCKOUT Trip Point-On Trip Point-Off POWER SUPPLY Operating Range Quiescent Current Turn-Off Current OVERVOLTAGE COMPARATOR Threshold ADP3810 ADP3811 Response Time
Conditions VCTRL VCTRL VCTRL
Symbol
-315
VCTRL AVCS IBCTRL
-1.0 Option Option 12.6 Option 16.8 Option AVBAT VREF -1.0 -1.8 -0.25 IOUT VSAT AVOUT 0.004 2.65
-2.5 2.000
+2.5
ILOAD
IOUT VCC-VOUT
Percent Above Full Scale5 Percent Above Full Scale5 IOUT from
VOV% VOV%
NOTES resistor from current sense voltage pin. Applies 12.6 16.8 options. Includes error from offset voltage, bias current, resistor divider voltage reference. Does include attenuation input resistor divider ADP3810. load capacitor required reference operation. Full scale programmed final battery voltage: 12.6 16.8 ADP3810 SENSE ADP3811. limits temperature extremes guaranteed correlation using standard Statistical Quality Control (SQC) methods. Specifications subject change without notice.
REV.
ADP3810/ADP3811
ABSOLUTE MAXIMUM RATINGS CONFIGURATION
VSENSE COMP
Supply Voltage, -0.4 VCTRL, Input Range -0.4 VSENSE Input Range (ADP3811) -0.4 VSENSE Input Range (ADP3810) -0.4 Maximum Power Dissipation Operating Temperature Range -40°C +85°C Storage Temperature Range -65°C 150°C Lead Temperature (Soldering, sec) +300°C
ORDERING GUIDE
ADP3810 ADP3811
VREF
VIEW (Not Scale) VCTRL
DESCRIPTION
Mnemonic Function
Model ADP3810AR-4.2 ADP3810AR-8.4 ADP3810AR-12.6 ADP3810AR-16.8 ADP3811AR
Temperature Range -40°C +85°C -40°C +85°C -40°C +85°C -40°C +85°C -40°C +85°C
Package Option SO-8 SO-8 SO-8 SO-8 SO-8
Battery Voltage 12.6 16.8 Adjustable
VSENSE VREF COMP VCTRL
Battery Voltage Sense Input. Current Sense Input. Reference Output. Nominally External Compensation Pin. Optocoupler Current Output Drive. Control Input Current Limit, Positive Supply. Ground Pin.
VBAT CTRL DC/DC CONVERTER 2.0V 0.1µF 0.1µF ADP3811 ONLY ICHARGE RETURN VRCS BATTERY
VREF 1.5M VCTRL
UVLO UVLO
VREF
VSENSE ADP3810 ONLY
BUFFER
ADP3810/ ADP3811
VREF
UVLO IOUT 1.2V 100µA
COMP
Figure Simplified Battery Charger
CAUTION (electrostatic discharge) sensitive device. Electrostatic charges high 4000 readily accumulate human body test equipment discharge without detection. Although ADP3810/ADP3811 features proprietary protection circuitry, permanent damage occur devices subjected high energy electrostatic discharges. Therefore, proper precautions recommended avoid performance degradation loss functionality.
WARNING!
SENSITIVE DEVICE
REV.
ADP3810/ADP3811-Typical Performance Characteristics
TYPICAL PARTS
REFERENCE VOLTAGE Volts
DROPOUT VOLTAGE
2.002
+10V 100µA 0.1µF
+10V 0.1µF
REFERENCE DROPOUT VOLTAGE Volts
2.004
0.14 +10V 0.1µF
0.12
2.000
0.10
1.998
0.08
1.996
0.06
1.994
TEMPERATURE
LOAD CURRENT
0.04
TEMPERATURE
Figure Reference Output Voltage Temperature Typical Parts
Figure Reference Drop-Out Volt (VCC-VREF) Load Current
Figure Reference Dropout Voltage Temperature
REFERENCE NOISE DENSITY nV/Hz
3000
CHARGE CURRENT Amps
+10V 100µA 0.1µF
2500
+10V 100µA 0.1µF
0.25
PSRR
2000
1500
1000
100k FREQUENCY
FREQUENCY
CONTROL VOLTAGE, VCTRL Volts
Figure Reference PSRR Frequency
Figure Reference Noise Density Frequency
Figure Charge Current Control Voltage
-294
-294
CURRENT SENSE VOLTAGE
CURRENT SENSE VOLTAGE
+10V -296
+10V -296
OPEN-LOOP GAIN
PHASE GAIN
COMP 0.01µF +25°C +10V
-300
-300
-302
-302
-304
-304 TEMPERATURE
SUPPLY VOLTAGE, Volts
100k FREQUENCY
Figure Full-Scale Current Sense Voltage Temperature
Figure Full-Scale Current Sense Voltage
Figure Open-Loop Gain Phase Frequency
REV.
PHASE SHIFT Degrees
-298
-298
ADP3810/ADP3811
VOLTAGE SENSE ACCURACY
GAIN
VOLTAGE SENSE ACCURACY
OPEN-LOOP GAIN
PHASE
COMP 0.01µF +25°C +10V
+10V
+25°C
PHASE SHIFT Degrees
-0.5
-0.5
-1.0
-1.0
100k FREQUENCY
-1.5
-1.5
TEMPERATURE
SUPPLY VOLTAGE, Volts
Figure Open-Loop Gain Phase Frequency
Figure ADP3810 Voltage Sense Accuracy Temperature
Figure ADP3810 Voltage Sense Accuracy
+10V
OFFSET
+25°C
+10V
VSENSE BIAS CURRENT
SUPPLY VOLTAGE, Volts
OFFSET
-0.5
-0.5
-1.0
-1.0
-1.5
TEMPERATURE
-1.5
TEMPERATURE
Figure ADP3811 Offset Temperature
Figure ADP3811, Offset
Figure ADP3811 VSENSE Bias Current Temperature
+25°C
VSENSE BIAS CURRENT
+10V +25°C
+10V
QUANTITY Parts
VOV%
VOV%
SUPPLY VOLTAGE, Volts
TEMPERATURE
Figure ADP3811 VSENSE Bias Current
Figure Overvoltage Comparator Distribution (VOV%)
Figure Overvoltage Comparator Threshold (VOV%) Temperature
REV.
ADP3810/ADP3811
+10V +25°C
VOUT +1.0V
VOUT/VCOMP
0.25 +10V LOAD
-40°C +25°C +85°C
OUTPUT SATURATION VOLTAGE, VSAT Volts
0.20
QUANTITY Parts
0.15
0.10
OUTPUT GAIN (VOUT/VCOMP)
0.05
Volts
TEMPERATURE
Figure Output Gain (VOUT/VCOMP) Distribution
Figure Output Gain (VOUT/VCOMP)
Figure VSAT Temperature
APPLICATIONS SECTION Functional Description
Description Battery Charging Operation
ADP3810 ADP3811 designed charging NiCad, NiMH LiIon batteries. Both parts provide accurate voltage sense current sense circuitry control charge current final battery voltage. Figure shows simplified battery charging circuit with ADP3810/ADP3811 controlling external dc-dc converter. converter many different types such Buck converter, Flyback converter linear regulator. cases, ADP3810/ADP3811 maintains accurate control current voltage loops, enabling cost, industry standard dc-dc converter without compromising system performance. Detailed realizations complete circuits including dc-dc converter included later this data sheet. ADP3810 ADP3811 contain following blocks (shown Figure "GM" type error amplifiers control current loop (GM1) voltage loop (GM2). common COMP node shared both amplifiers such that network this node helps compensate both control loops. precision reference used internally available externally other circuitry. bypass capacitor shown required stability. current limited buffer stage (GM3) provides current output, IOUT, control external dc-dc converter. This output directly drive optocoupler isolated converter applications. dc-dc converter must have control scheme such that higher IOUT results lower duty cycle. this case, simple, single transistor inverter used control phase inversion. amplifier buffers charge current programming voltage, VCTRL, provide high impedance input. UVLO circuit shuts down amplifiers output when supply voltage (VCC) falls below This protects charging system from indeterminate operation. transient overshoot comparator quickly increases IOUT when voltage input rises over above VREF. This clamp shuts down dc-dc converter quickly recover from overvoltage transients protect external circuitry.
based system shown Figure charges battery with current supplied dc-dc converter, which most likely switching type supply could also linear supply where feasible. value charge current controlled feedback loop comprised RCS, GM1, external dc-dc converter voltage VCTRL input. actual charge current voltage, VCTRL, dependent upon choice values according formula below:
CHARGE CTRL
Typical values 0.25 which result charge current control voltage resistor internal trimmed absolute value. positive input referenced ground, forcing virtual ground. resistor converts charge current into voltage VRCS, this voltage that regulating. voltage VRCS equal -(R3/80 VCTRL. When VCTRL equals VRCS equals -250 VRCS falls below programmed level (i.e., charge current increases), negative input goes slightly below ground. This causes output source more current drive COMP node high, which forces current, IOUT, increase. higher IOUT decreases drive dc-dc converter, reducing charging current balancing feedback loop. battery approaches final charge voltage, voltage loop takes over. system becomes voltage source, floating battery constant voltage thereby preventing overcharging. constant voltage feature also protects circuitry that actually powered battery from overvoltage battery removed. voltage loop comprised dc-dc converter. final battery voltage simply ratio according following equation (VREF 2.000
2.000V
battery voltage rises above programmed voltage, VSENSE pulled above VREF. This causes source more current, raising COMP node voltage IOUT. with REV.
ADP3810/ADP3811
current loop, higher IOUT reduces duty cycle dc-dc converter causes battery voltage fall, balancing feedback loop. Each stage designed asymmetrical that each amplifier only source current. outputs tied together COMP node loaded with internal constant current sink approximately Whichever amplifier sources more current controls voltage COMP node therefore controls feedback. This scheme realization analog "OR" function where control dc-dc converter charging circuitry. Whenever circuit full current limiting full voltage limiting, respective stage sources identical amount current fixed current sink. other stage sources zero current loop. transition region, both stages source some current comprise full amount current sink. high gains ensure smooth sharp transition from current control voltage control. Figure shows graph transition from current voltage mode, that measured circuit Figure detailed below. Notice that current stays full programmed level until battery within final programmed voltage this case), which maintains fast charging through almost battery voltage range. This improves speed charging compared scheme that reduces current lower battery voltages. second element battery charging system some form dc-dc converter. achieve high efficiency, dc-dc converter isolated off-line switching power supply, isolated nonisolated Buck other type switching power supply. lower efficiency requirements, linear regulator from wall adapter used. above discussion, current, IOUT, controls duty cycle switching supply; case linear regulator, IOUT controls pass transistor drive. Examples these topologies shown later this data sheet. off-line supply such flyback converter used, isolation between control logic ADP3810/ADP3811 required, optocoupler inserted between ADP3810/ADP3811 output control input primary side PWM.
Charge Termination
program VCTRL input charge current. high impedance VCTRL enables inclusion filter integrate output into control voltage.
Compensation
voltage current loops have significantly different natural crossover frequencies battery charger application, loops most likely need different pole/zero feedback compensation. Figure shows single network from COMP node ground. This primarily frequency compensation (fC< voltage loop. Since COMP node shared both stages, this compensation also affects current loop. internal resistor does change zero location compensation current loop with respect voltage loop. provide separate higher frequency compensation kHz-10 kHz), second series needed. detailed calculation compensation values given later this data sheet.
ADP3810 ADP3811 Differences
main difference between ADP3810 ADP3811 illustrated Figure resistors external ADP3811 internal ADP3810. ADP3810 specifically designed LiIon battery charging, thus, internal resistors precision thin-film resistors laser trimmed LiIon cell voltages. Four different final voltage options available ADP3810: 12.6 16.8 slightly different voltages accommodate different LiIon chemistries, please contact factory. ADP3811 does include internal resistors, allowing designer choose final battery voltage appropriately selecting external resistors. Because ADP3810 specifically LiIon batteries, reference trimmed tighter accuracy specification instead ADP3811.
VCTRL Input Charge Current Programming Range
system charging LiIon battery, main criteria determine charge termination absolute battery voltage. ADP3810, with accurate reference internal resistors, accomplishes this task. ADP3810's guaranteed accuracy specification final battery voltage ensures that LiIon battery will overcharged. This especially important with LiIon batteries because overcharging lead catastrophic failure. also important insure that battery charged voltage equal optimal final voltage (typically cell). Stopping less than full-scale results battery that been charged full capacity, reducing battery's time equipment's operating time. ADP3810/ADP3811 does include circuitry detect charge termination criteria such -V/t T/t, which common NiCad NiMH batteries. such charge termination schemes required, cost microcontroller added system monitor battery voltage temperature. output from microcontroller subsequently REV.
voltage VCTRL input determines charge current level. This input buffered internal single supply amplifier (labeled BUFFER) allow easy programmability VCTRL. example, fixed charge current, VCTRL resistor divider from reference output. microcontroller setting charge current, simple filter VCTRL enables voltage output from micro. course, digital-to-analog converter could also used, high impedance input makes output economical choice. bias current VCTRL typically which flows pin. guaranteed input voltage range buffer from When VCTRL range output internal amplifier fixed This corresponds charge current 0.25 graph charge current versus VCTRL Figure shows this relationship. Figure shows diode series with buffer's output resistor from VREF this output. diode prevents amplifier from sinking current, small input voltages buffer open output. resistor forms divider with internal resistor output i.e., about maximum current. This corresponds typical trickle charge current level NiCad batteries. When VCTRL rises above buffer sources current output follows input. total range VCTRL from results charge current range from (for 0.25 Larger
ADP3810/ADP3811
charge current levels obtained either reducing value increasing value main penalty increasing lower efficiency larger voltage drop across RCS, penalty decreasing lower accuracy (but higher efficiency) discussed below.
VREF Output
internal band reference only used internally voltage current loops, also available externally accurate voltage needed. reference employs output transistor dropout operation. Figure shows typical graph dropout voltage versus load current. reference guaranteed source with dropout voltage less. capacitor reference integral compensation reference therefore required stable operation. desired, larger value capacitance also used application, smaller value should used. This capacitor should located close VREF pin. Additional reference performance graphs shown Figures through
Output Stage
ADP3810 specified with respect final battery voltage. This tested full feedback loop that single accuracy specification given specification table accounts errors mentioned above. ADP3811, resistors external, final voltage accuracy needs determined designer. Certainly, tolerance resistors large impact final voltage accuracy, better recommended.
Supply Range
output stage performs important functions. buffer compensation node, such, high impedance input. also stage. current output enable direct drive optocoupler isolated applications. gain from COMP node approximately mA/V. With load resistor voltage gain equal five specified data sheet. different load resistor results gain equal mA/V). Figures show gain varies from part part versus supply voltage, respectively. guaranteed output current which much more than typical required most applications.
Current Loop Accuracy Considerations
supply range specified from However, final battery voltage option ADP3810 16.8 16.8 divided down thin film resistors internally. Thus, input never sees much more than which well below voltage limit. fact, fixed ADP3810 will still control charging 16.8 battery stack. ADP3811, with external resistors, charge batteries voltages well excess supply voltage. However, final battery voltage above cannot supplied directly from battery Figure Alternative circuits must employed will discussed later. Decoupling capacitors should located close supply pin. actual value capacitors depends application, very least capacitor should used.
OFF-LINE, ISOLATED, FLYBACK BATTERY CHARGER
accuracy current loop dependent several factors such offset GM1, offset VCTRL buffer, ratio internal compared external resistor, accuracy RCS. specification current loop accuracy states that full-scale current sense voltage, VRCS, -300 guaranteed within this value. This assumes exact resistor errors this resistor will result further errors charge current value. example, error resistor value will error charge current. same true RCS, current sense resistor. Thus, better resistors recommended. mentioned above, decreasing value increases charge current. Since VRCS that specified, actual value accounted specification. example where illustrates impact accuracy charge current. range VRCS from -300 This results charge current range from opposed charge current range 0.25 Thus, only minimum current changed, absolute variation around point increased (although percentage variation same).
Voltage Loop Accuracy Considerations
ADP3810 ADP3811 ideal isolated chargers. Because output stage directly drive optocoupler, feedback control signal across isolation barrier simple task. Figure shows complete flyback battery charger with isolation provided flyback transformer optocoupler. essential operation circuit much different from simplified circuit described Figure loop controls charge current, loop controls final battery voltage. dc-dc converter block comprised primary side circuit flyback transformer, control signal passes through optocoupler. circuit Figure incorporates features necessary assure long battery life with rapid charging capability. using ADP3810 charging LiIon batteries, ADP3811 NiCad NiMH batteries, component count minimized, reducing system cost complexity. With circuit presented with many possible variations, designers longer need compromise charging performance battery life achieve cost effective system.
Primary Side Considerations
typical current-mode flyback controller chosen primary control circuit several reasons. First most importantly, capable operating from very small duty cycles near maximum designed duty cycle. This makes good choice wide input supply voltage variation requirement, which usually between V-270 world wide applications. that additional requirement 100% current control, duty cycle must have wide range. This charger achieves these ranges while maintaining stable feedback loops. detailed operation design primary side widely described technical literature detailed here. However, following explanation should make clear reasons primary side component choices. frequency around reasonable compromise REV.
accuracy voltage loop dependent offset GM2, accuracy reference voltage, bias current through ratio R1/R2. demanding application charging LiIon batteries, accuracy
ADP3810/ADP3811
10nF 1N4148 22µF 50µF/450V TX1** 120/220V- 330pF 3.3k 3.3k COMP OUTPUT 0.1µF 0.1µF ISENSE 470pF VREF RT/CT TOLERANCE 120kHz 750µH LSEC 7.5µH 3.3k 2.2nF OPTO COUPLER MOC8103 0.1µF VREF VSENSE VCTRL 0.1µF CHARGE CURRENT CONTROL VOLTAGE 0.2µF IRFBC30 MAXIMUM VOUT +10V CHARGE CURRENT 0.1A 47µF 100k 1N4148 22nF MURD320 20k* 1.2k 80.6k* 20k* 3.3V 220µF VOUT BATTERY
0.25*
3845
ADP3810/ADP3811
COMP
Figure ADP3810/ADP3811 Controlling Off-Line, Flyback Battery Charger
between inductive capacitive component sizes, switching losses cost. primary PWM-IC circuit derives starting through resistor directly from rectified input. After startup, conventional bootstrapped sourcing circuit from auxiliary flyback winding wouldn't work, since flyback voltage would reduced below minimum level specified 3845 under shorted discharged battery condition. Therefore, voltage doubler circuit developed shown Figure that provides minimum required across specified voltage range even with shorted battery. While signal from ADP3810/ADP3811 controls average charge current, primary side should have cycle cycle limit switching current. This current limit designed that, with failed malfunctioning secondary circuit optocoupler, primary power circuit components (the transformer) won't overstressed. addition, during start-up shorted battery, ADP3810/ ADP3811 won't present. Thus, primary side current limit only control charge current. secondary side rises above ADP3810/ADP3811 takes over controls average current. primary side current limit current sense resistor connected between power NMOS transistor, IRFBC30, ground. current drive ADP3810/ADP3811's output stage directly connects photodiode optocoupler with additional circuitry. With output current, output stage drive variety optocouplers. MOC8103 shown example. current photo-transistor flows through feedback resistor, RFB, setting voltage 3845's COMP pin, thus controlling duty cycle. controlled switching regulator should designed shown that more current from optocoupler reduces duty cycle converter. Approximately should REV.
maximum current needed reduce duty cycle zero. difference between drive requirement leaves ample margin variations optocoupler gain.
Secondary Side Considerations
lowest cost, current-mode flyback converter topology used. Only single diode needed rectification (MURD320 Figure 23), filter inductor required. diode also prevents battery from back driving charger when input power disconnected. capacitor filters transformer current, providing average current charge battery. resistor, RCS, senses average current which controlled input. this case, charging current high ripple flyback architecture, low-pass filter CC2) current sense signal needed. This filter extra inverted zero improve phase margin loop. capacitor connected between VOUT 0.25 sense resistor. provide additional decoupling ground, capacitor also connected VOUT. Output ripple voltage critical, output capacitor selected lowest cost instead lowest ripple. Most ripple current shunted parallel battery, connected. needed, high frequency ringing caused circuit parasitics damped with small snubber across rectifier. source ADP3810/ADP3811 come from direct connection battery long battery voltage remains below specified operating range. battery voltage less then (e.g., with shorted battery, battery discharged below it's minimum voltage), ADP3810/ ADP3811 will Undervoltage Lock (UVLO) will drive optocoupler. this condition, primary circuit will designed current limit. ADP3810/ADP3811 boosted using circuit shown Figure This circuit keeps above long
ADP3810/ADP3811
battery voltage least with programmed charge current higher programmed charge current, battery voltage drop below still maintained above This because additional energy flyback transformer, which transfers more energy through capacitor VCC. bypass capacitor stores energy transferred through capacitor.
Secondary Side Component Calculations Design Criteria:
Battery Charge Current Battery Voltage characteristics four different charge current settings given Figure high gain internal amplifiers ensures sharp transition between current mode voltage mode regardless charge current setting. fact that current remains full charging until battery very close final voltage ensures fast charging times. transient performance various turn-on turn-off conditions detailed Figures Figure shows output voltage when power applied with battery connected. shown, output voltage quickly rises overshoots voltage. internal comparator responds this clamps voltage giving quick recovery. Without internal comparator, external zener would required clamp voltage anode. Figure shows battery current when connecting disconnecting battery. actual trace shown voltage across RCS, which negative current flowing into battery. There overshoot when battery connected, loop quickly takes control limits average current programmed 0.75 When battery removed, current quickly returns zero. solid band scope current rising falling with switching PWM. time scale slow show detail this. Figure shows output voltage when battery stack charged connected then disconnected. expected, when battery connected, voltage immediately goes When battery disconnected, voltage returns programmed float voltage Again, small overshoot present that clamped internal comparator.
BATTERY 220VAC
Charging cell NiCad battery. Individual Cell Voltage: VCELLMAX 1.67 Battery Stack Voltage: VOMAX 1.67 Charge Current: IOMAX Control Voltage: VCTRL (for IOMAX Fixed Value: Pick Value 80.6 voltage limit approximately above maximum fully charged voltage when -V/t termination used. This limit gives second level protection without interfering with -V/t charge termination.
Component Value Calculations:
Current Sense Resistor: Battery Divider,
VCTRL/(4 IOMAX) 1/(4 0.25 VREF R1/(VOMAX-VREF) 80.6 k/(10 20.15 Pick 20.0
final voltage charge current accuracy dependent upon resistor tolerances. Choose appropriate tolerances desired accuracy. percent accuracy recommended.
Charger Performance Summary
charger circuit properly executes charging algorithm exhibiting stable operation regardless battery conditions, including open circuit load. circuit charge other battery voltages modifying only battery voltage sense divider. would expected, circuit efficiency best high battery voltages. Replacing output blocking rectifier diode with Schottky would improve efficiency Schottky's leakage could tolerated, reverse voltage rating application requirement.
VCTRL 1.0V ILIMIT VOUT VCTRL 0.25V VCTRL 0.125V VCTRL 0.5V
2V/DIV
0.1sec/DIV
Figure Flyback Charger Output Voltage Transient Power Turn Battery Attached
0.0V
-200mV
VCTRL 0.775V 220VAC
0.2V/DIV
20msec/DIV
Figure Charge Current Battery Voltage Four Settings Flyback Charger Figure
Figure Charge Current Transient Response Battery Connect/Disconnect
-10-
REV.
ADP3810/ADP3811
220VAC VCTRL
options could used, ADP3811 could substituted with external resistors user voltage. Notice grounds circuit. ground high current return source other ground ADP3810 circuitry. separates grounds, important keep them separate shown. adjustable version ADP1148 used this circuit instead fixed output version. output voltage back into pin, which regulate VBAT Doing provides secondary, higher voltage limit without interfering with normal circuit operation. control output ADP3810 connected through resistor SENSE+ input ADP1148. current, IOUT, adjusts level SENSE+ pin, which added current ramp across RSENSE. Higher IOUT increases voltage SENSE+ reduces duty cycle 1148, giving negative feedback. circuit shown quickly safely charge LiIon batteries while maintaining high efficiency. efficiency ADP1148 only degraded slightly addition ADP3810 external circuitry. supply current lowers overall efficiency approximately 1%-2% maximum output current. 0.25 sense resistor further lowers efficiency power loss high output currents. efficiency discussion ADP1148 data sheet more information.
Linear Regulator
2V/DIV
50msec/DIV
Figure Output Voltage Transient Response Battery Connect/Disconnect
NONISOLATED TOPOLOGIES Buck Switching Regulators
ADP3810/ADP3811 ADP1148 combined create high efficiency buck regulator battery charger shown Figure ADP1148 high efficiency, synchronous, step-down regulator that controls external MOSFETs shown. Similar previous flyback circuit, ADP3810 controls average charge current final battery voltage, ADP1148 controls cycle cycle current. following discussion explains functionality circuit does into detail ADP1148. more information, ADP1148 data sheet details operation device gives formulas choosing external components. resistor RSENSE sets cycle cycle current limit which enough above average current ADP3810 loop avoid interfering still provides safe maximum current protect external components. ADP3810 uses 0.25 resistor, RCS, sense battery current. before, resistor needed between input ADP3810. network from ground performs dual function filtering compensation. voltage loop directly senses battery voltage. Since ADP3810 used this circuit instead ADP3811, VSENSE connected directly battery. internal resistors battery voltage this case. course, other voltage
third charging circuit shown Figure this case, switching supply replaced with linear regulator. ADP3811 drives gate N-channel MOSFET using external 2N3904. before, ADP3811 senses charge current through 0.25 resistor. When current increases above limit, internal amplifier causes output high. This puts more voltage across increasing current current increases, gate pulled lower, reducing gate source voltage decreasing charge current complete feedback loop. Because ADP3811 current output, external resistor needed from ground order convert current voltage.
+VIN 0.1µF
IRF7204
100µF 62µH RSENSE**
VSENSE VREF 0.1µF VCTRL 0.1µF CTRL VCTRL COMP VREF NORMAL >1.5V SHUTDOWN
DRIVE SHUTDOWN SENSE+ 220nF 68pF DRIVE
VBAT
1000pF BATTERY COUT 220µF 10BQ040 0.25
ADP3810
ADP1148
SENSE-
IRF7403
COILTRONICS CTX-68-4 SL-1-C1-0R068J
Figure High Efficiency Buck Battery Charger
REV.
-11-
ADP3810/ADP3811
VBAT IRF7201 0.1µF 80.6k VSENSE VREF 0.1µF VCTRL VCTRL VREF 0.1µF VCTRL COMP VREF 220nF 220µF VBAT 2.0V BATTERY 2N3904 +VIN
ADP3811
0.25* 20k*
Figure ADP3811 Controlling Linear Battery Charger
trade-off between using linear regulator shown versus using flyback buck type charger efficiency versus simplicity. linear charger Figure very simple, uses minimal amount external components. However, efficiency poor, especially when there large delta between input output voltages. power loss pass transistor equal (VIN-VBAT) ICHARGE. Since circuit powered from wall adapter, efficiency concern, heat dissipated pass transistor could excessive. important specification this circuit dropout voltage, which difference between input output voltage full charge current. There must enough voltage keep N-channel MOSFET this case, dropout voltage approximately output current. alternative
IRF7205 ADP3811 VREF 2N3904 ADP3811 ADP3811 2N3904 VBAT 2N3904 2N5058 VBAT
charger application, loops need different inverted zero feedback loop compensations that accomplished series networks. provides needed frequency (typical compensation voltage loop, other provides separate high frequency kHz-10 kHz) compensation current loop. addition, current loop input requires ripple reduction filter filter switching noise. Instead placing both networks COMP pin, current loop network placed between ground shown Figure (CC2 RC2). Thus, performs functions, ripple reduction loop compensation.
Loop Stability Criteria Battery Charger Applications
voltage loop stable when battery removed floating. current loop stable when battery being charged within specified charge current range. Both loops have stable within specified input source voltage range.
Flyback Charger Compensation
P-Channel MOSFET Darlington Figure Alternative Pass Transistor Linear Regulator
realizations pass element shown Figure case (a), pass transistor P-channel MOSFET. This provides lower dropout voltage that VBAT within hundred millivolts VIN. case (b), Darlington configuration transistors used. dropout voltage this circuit approximately charge current.
STABILIZATION FEEDBACK LOOPS
ADP3810/ADP3811 uses transconductance error amplifiers with "merged" output stages create shared compensation point (COMP) both current voltage loops explained previously. Since voltage current loops have significantly different natural crossover frequencies battery
Figure shows simplified form battery charger system based off-line flyback converter presented Figure With some modifications optocoupler, example), this model also used converters such Buck Converter (Figure Linear Regulator (Figure 29). internal amplifiers ADP3810/ADP3811, buffered output stage that drives optocoupler. primary side Figure represented here "Power Stage," which modeled GM4, linear voltage controlled current source model flyback transformer switch. "Voltage Error Amplifier" block internal error amplifier 3845 PWM-IC Figure 23), followed internal resistor divider. optocoupler modeled current controlled current source shown. output current develops voltage, across gain values blocks defined below. This linear model makes calculation compensation values manageable task. also great benefit allowing simulation response using circuit simulator, such PSpice MicroCap. computer modeling,
-12-
REV.
ADP3810/ADP3811
VBAT 80.6k BATTERY
POWER STAGE
1.2k
0.25 0.2µF
220µF
0.33V/V COMP VCTRL 1.0V
2.0V
VSENSE
3.3k
8.3mA/V
2.1mA/V
VOLTAGE ERROR AMPLIFIER
6mA/V OPTO COUPLER ITXOC 0.36mA/mA
ADP3810/ ADP3811
400k COMP
Figure Block Diagram Linearized Feedback Model
amplifiers represented voltage controlled current sources, optocoupler current controlled current source, error amplifier voltage controlled voltage source.
Design Criteri
Charging cell NiCad battery. Battery Stack Voltage: VOMAX 1.67 Charge Current: IOMAX Fixed Value: Pick value 80.6 Calculated Current Sense Resistor: 0.25 Calculated Voltage Sense Divider: Output Filter Cap: (ESR Filter Cap: (ESR
Gain Each Block
these stages value times load resistance. COMP pin, internal load resistance, typically optocoupler gain typical value taken from MOC8103 data sheet. voltage error amplifier gain resistor divider internal 3845 only. output internal amplifier, labeled Figure actual assumed have sufficient open-loop gain bandwidth compared system bandwidth; result, considered ideal transimpedance amplifier. pole created capacitor parallel with high enough frequency affect compensation. power stage gain equation linearized based primary side current mode control with flyback transformer operating with discontinuous inductor current. IOMAX maximum change output current, which equal IOMAX-IOMIN. Since minimum current IOMAX IOMAX maximum change control voltage internal circuitry within 3845 load resistor, RLOAD, different voltage current loop cases. voltage loop without battery, effective load current loop, effective load RCS. current loop, voltage limit been reached, maximum output voltage equal maximum output current times load resistor. Thus, entire expression under square root reduces 1.0. Substituting these values into general equation power stage yields specific gain values shown GM4. When calculating loop gain voltage loop current loop, there main differences. First, applies only voltage loop, applies only current loop. appropriate input stage particular loop calculations. Second, there three battery conditions consider. current loop, battery present uncharged. Thus, battery modeled very large capacitance (greater than Farad). voltage loop, battery -13-
ADP3810/ADP3811 Input: ADP3810/ADP3811 VSENSE Input: ADP3810/ADP3811 Output Buffer: Optocoupler: Voltage Error Amplifier: Power Stage (General): Power Stage (Voltage Loop): Power Stage (Current Loop):
mA/V mA/V mA/V ITXoc 0.36 mA/mA VC/VX 0.333 OMAX RLOAD 0.091
IOMAX OMAX
gains ADP3810/ADP3811 amplifiers based typical measurements IC's open-loop gain, they expressed units milliamps volt. voltage gain REV.
ADP3810/ADP3811
either present absent. battery present, large capacitance creates very frequency dominant pole, giving single pole system. more demanding case when battery removed. output pole dependent upon filter capacitors, CF2. This pole higher frequency, more care must taken stabilize loop response. three cases described detail below. following calculations compensation components help realize stable voltage current loops. practical designs, checking stability using network analyzer Feedback Loop Analyzer always recommended. calculated component values serve good starting values measurementbased optimization. component values shown Figure slightly different from calculated values based this optimization procedure. simplify analysis further, loop gain split into components: gain from battery ADP3810/ ADP3811's COMP gain from COMP back battery. Because compensation each loop depends upon network COMP pin, convenient choice dividing loop calculations.
Definitions: Step Pick voltage current loop crossover frequencies, fCI:
avoid interference between voltage loop current loop, 1/10 fCI, current loop crossover. current loop crossover chosen provide fast current limiting response time, pick
Step Calculate GMOD fCV:
modulator gain 46.7 gain. modulator pole reduces this gain above fPM.
GMOD (100 GMOD (dc)-
(100 48.3 -10.9 0.11
Step Calculate gain loss fCV:
have feedback loop gain cross over (100 should +10.9 Thus, total gain loss needed crossover GLOSS (dc) (100 48.5 10.9 37.6
Step Determine needed achieve LOSS:
Modulator Gain: GMOD gain from COMP VBAT. Error Amplifier: gain from VBAT COMP pin. Loop Gain: GLOOP GMOD GEA. Modulator Pole: fPM, pole present output modulator. Modulator Zero: fZM, zero ESR, RF1, filter cap, CF1.
Voltage Loop Compensation, Battery Step Calculate loop gain LOOP), fPM, fZM:
GMOD
achieve this GLOSS need pole, which located COMP pin. practically parasitic loss gain first parasitic pole occurs approximately shown Figure Thus, entire gain loss must realized with external compensation capacitor, CC1, that sets pole, fP1.
GLOSS
Step Calculate based upon
0.36 GMOD 48.3 0.333 0.091
Step Calculate loop phase margin,
loop phase margin combination phase modulator pole zero error amplifier pole.
2.1mA 48.5
GLOOP 44.5 48.3 96.8
0.11 (1.22
Step Calculate stabilize loop:
phase losses modulator error amplifier results loop phase which unacceptable loop stability. stabilize feedback loop, have phase boosting zero error amplifier inserting resistor (RC1) series with capacitor CC1. desired phase margin degrees, frequency zero calculated: fCV/tan From this, resistor calculated:
reality, interaction their ESRs create additional pole/zero pair, because value (ESR CF1) (ESR CF2) similar, they tend cancel each other out. Furthermore, loop crossover order magnitude lower frequency, additional pole zero have little effect loop response.
-14-
REV.
ADP3810/ADP3811
Step Iterate CC1: Current Loop Compensation
Because very close fCV, will increase error amplifier gain nonnegligible amount point. increase gain calculated
7.1dB
that voltage loop compensation complete, time compensation current loop. definitions modulator gain error amplifier gain same before; now, controlling error amplifier Figure opposed GM2, voltage loop. Otherwise, calculations very similar.
Step Calculate loop gain LOOP), fPM, fZM:
GMOD
0.36 -4.5 0.333 0.25
Now, total error amplifier gain loss required GLOSS 37.6 44.7 With this, calculated from equation Step 0.58 Finally, recalculated using equation Step
0.58
[8.3 70.4
GLOOP -6.1 70.4 64.3
RF1) 0.35
Following these steps gives cookbook method calculating compensation components voltage loop. mentioned above, these components optimized actual circuit. results PSpice1 analysis loop shown Figure open loop gain loop calculated. crossover frequency with phase margin 52°. graph shows phase leveling 90°. reality phase will continue fall higher frequency parasitic poles take effect.
=1.6
Step Pick current loop crossover frequency,
From Step voltage loop calculations, kHz.
Step Calculate GMOD fCI:
PSpice trademark MicroSim Corporation.
PHASE Degrees
modulator gain -4.5 gain. modulator pole reduces this gain above fPM.
(1.9
PHASE MARGIN
GAIN
CROSSOVER -100 0.01
capacitor much higher ESR, e.g., modulator zero, fZM, will lower frequency than modulator pole, fPM. This causes loop gain bandwidth increase could cause instability. possible solution this scenario much higher value capacitor. pole this capacitor would then range would reduce loop gain. much less than bandwidth loop will decrease slightly.
100k
(1.9 -4.5 -12.7 -13.4
FREQUENCY
Step Calculate gain loss fCI:
Figure Voltage Loop Gain/Phase Plots
Voltage Loop Compensation, Battery Present
When battery finished charging still connected charging circuitry, system said "floating" battery. loop maintaining constant output voltage equal battery voltage, output current dropped nearly zero. This case actually easiest compensate because battery's capacitance creates very frequency dominant pole, giving single pole response. example, battery modeled Farad capacitor, dominant pole will 1/(2 0.013 MHz. This very frequency pole causes system cross over less than giving stable single pole system. compensation components have little effect this response, further calculations needed this case. REV.
gain loss current loop combination loss CC1, additional loss from CC2, RC2. calculate contribution gain roll-off needed from CC2, RC2, effective gain must first calculated. Since gain calculated kHz, impedance Thus, gain becomes:
(1.9 +120
(1.9 (10320 38.9
GLOSS (1.9 kHz) GMOD (1.9 kHz) 38.9 13.4 25.5
-15-
ADP3810/ADP3811
Step Calculate value realize GLOSS:
Assuming that short, forms resistor divider with reducing loop gain. calculate RC2, simply resistor ratio give attenuation 25.5 which loss 1/20.
provide some margin circuit gain fluctuations various stages, final value adjusted down
Step Calculate value
maintain high gain, capacitor, CC2, connected series with RC2. zero provided this network should close provide phase boost crossover:
final phase margin 115° more than adequate stable current loop. reality, higher order parasitic poles reduce phase margin significantly less than 115° crossover. same case voltage loop because cross over frequency well below parasitic poles. PSpice analysis resulting loop gain phase values calculated shown Figure
PHASE Degrees
pole frequency calculated
PHASE MARGIN
Step Check current loop phase margin:
+arc
GAIN
CROSSOVER 0.01
115°
FREQUENCY
100k
Figure Current Loop Gain/Phase Plots
OUTLINE DIMENSIONS
Dimensions shown inches (mm).
8-Lead Small Outline (SO-8)
0.1968 (5.00) 0.1890 (4.80)
0.1574 (4.00) 0.1497 (3.80)
0.2440 (6.20) 0.2284 (5.80)
0.0098 (0.25) 0.0040 (0.10)
0.0688 (1.75) 0.0532 (1.35)
0.0196 (0.50) 0.0099 (0.25)
SEATING PLANE
0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35)
0.0098 (0.25) 0.0075 (0.19)
0.0500 (1.27) 0.0160 (0.41)
-16-
REV.
PRINTED U.S.A.
C2203-12-10/96
above formula subtracts phase each pole adds phase each zero. poles zeros come pairs, fP2/fZ2 calculated Step from CC2/RC2; fPM/fZM calculated Step output filter cap; fP1/fZ3 CC1/RC1. same pole that calculated Step needs recalculated with addition internal resistor follows:

Secondary Side, Off-Line Battery Charger Controllers ADP3810/ADP3811

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