Micropower DC-DC Converter Adjustable Fixed ADP1108 ADP1108
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FEATURES Operates Supply Voltages From Consumes Only Supply Current Step-Up Step-Down Mode Operation Minimum External Components Required Battery Detector Comparator On-Chip User-Adjustable Current Limit Internal Power Switch Fixed Adjustable Output Voltage Versions 8-Pin SO-8 Package APPLICATIONS Notebook/Palm Computers Converters Converters Bias Generators Peripherals Add-On Cards Battery Backup Supplies Cellular Telephones Portable Instruments
Micropower DC-DC Converter Adjustable Fixed ADP1108
ADP1108
GAIN BLOCK/ ERROR 1.245V REFERENCE ILIM OSCILLATOR DRIVER
COMPARATOR
ADP1108-3.3 ADP1108-5 ADP1108-12
GAIN BLOCK/ ERROR 1.245V REFERENCE OSCILLATOR DRIVER ILIM
GENERAL DESCRIPTION
ADP1108 highly versatile micropower switch-mode dc-dc converter that operates from input voltage supply typically starts from ADP1108 programmed into step-up step-down dc-to-dc converter with only three external components. fixed outputs adjustable version also available. step-up mode, supply voltage range step-down mode. ADP1108 deliver from cell input from input step-down mode. Switch current limit programmed with single resistor. battery operated power conscious applications, ADP1108 offers very power consumption less than auxiliary gain block available ADP1108 used battery detector, linear post regulator, under voltage lockout circuit error amplifier.
COMPARATOR 753k
ADP1108-3.3: 456k ADP1108-5: 250k ADP1108-12: 87.4k SENSE
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., 1997
ADP1108-SPECIFICATIONS unless otherwise noted)
Parameter QUIESCENT CURRENT QUIESCENT CURRENT, BOOST MODE CONFIGURATION
Symbol
Conditions Switch Load, +25°C ADP1108-3.3 ADP1108-5 ADP1108-12 Step-Up Mode Step-Down Mode ADP11081
Units
INPUT VOLTAGE COMPARATOR TRIP POINT VOLTAGE OUTPUT SENSE VOLTAGE
1.20 3.13 4.75 11.4 1.245 5.00 12.0 0.15 0.02
12.6 1.30 3.46 5.25 12.6 0.075 0.75 1.00
%/°C
VOUT
ADP1108-3.32 ADP1108-52 ADP1108-122 ADP1108 ADP1108-3.3 ADP1108-5 ADP1108-12
COMPARATOR HYSTERESIS OUTPUT HYSTERESIS
OSCILLATOR FREQUENCY DUTY CYCLE SWITCH TIME FEEDBACK BIAS CURRENT BIAS CURRENT GAIN BLOCK OUTPUT REFERENCE LINE REGULATION SWSAT VOLTAGE, STEP-UP MODE VSAT Full Load ILIM Tied VSET VREF ISINK VSET 1.00 +25°C +25°C 100K3 from ILIM VIN, +25°C
SWSAT VOLTAGE, STEP-DOWN MODE GAIN BLOCK GAIN CURRENT LIMIT CURRENT LIMIT TEMPERATURE COEFFICIENT SWITCH LEAKAGE CURRENT MAXIMUM EXCURSION BELOW VSW2
1000 -0.3
Measured Pin, +25°C 1SW1 Switch +25°C
-400
-350
NOTES This specification guarantees that both high trip points comparator fall within 1.20 1.30 range. output voltage waveform will exhibit sawtooth shape comparator hysteresis. output voltage fixed output versions will always within specified range. resistor connected between source pin. limits temperature extremes guaranteed correlation using standard Quality Control methods. Specifications subject change without notice.
REV.
ADP1108
ABSOLUTE MAXIMUM RATINGS* CONFIGURATIONS 8-Lead Plastic (N-8) 8-Lead SOIC (SO-8)
Supply Voltage (VIN) Voltage (VSW1) Voltage (VSW2) -0.5 Feedback Voltage (ADP1108) +5.5 Sense Voltage (ADP1108, 3.3, Maximum Power Dissipation Maximum Switch Current .1.5 Operating Temperature Range 170°C Storage Temperature Range -65°C +150°C Lead Temperature (Soldering, sec) +300°C
*Stresses above those listed under Absolute Maximum Ratings cause permanent damage device. This stress rating only; functional operation device these other conditions above those listed operational sections this specification implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ILIM
(SENSE)*
ILIM
(SENSE)*
ADP1108
VIEW (Not Scale)
VIEW (Not Scale)
ADP1108
FIXED VERSIONS
FIXED VERSIONS
FUNCTION DESCRIPTIONS
ORDERING GUIDE
Mnemonic Package* SO-8 SO-8 SO-8 SO-8 ILIM
Function normal conditions this connected VIN. When lower current required, resistor should connected between ILIM VIN. Limiting switch current achieved connecting resistor. Input Voltage. Collector Power Transistor. step-down configuration, connect VIN. step-up configuration, connect inductor/diode. Emitter Power Transistor. step-down configuration, connect inductor/diode. step-up configuration, connect ground. allow this more than diode drop below ground. Ground. Auxiliary Gain (GB) Output. open collector sink Gain Amplifier Input. amplifier positive input connected negative input connected 1.245 reference. ADP1108 (adjustable) version this connected comparator input. ADP1108-3.3, ADP1108-5 ADP1108-12, goes directly internal application resistor that output voltage.
Model ADP1108AN ADP1108AR ADP1108AN-3.3 ADP1108AR-3.3 ADP1108AN-5 ADP1108AR-5 ADP1108AN-12 ADP1108AR-12
Output Voltage
Plastic DIP, Small Outline Package.
FB/SENSE
CAUTION (electrostatic discharge) sensitive device. Electrostatic charges high 4000 readily accumulate human body test equipment discharge without detection. Although ADP1108 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.
ADP1108-Typical Performance Characteristics
SWITCH VOLTAGE Volts
1100 1000
SWITCH CURRENT
(SAT)
3.0V 2.0V 5.0V
(SAT) Volts
SWITCH CURRENT Amps
0.05
0.15 0.25 0.35 0.45 0.55 0.65 SWITCH CURRENT Amps
0.75
RLIM
Figure Saturation Voltage ISWITCH Current Step-Up Mode
Figure Switch Voltage Switch Current Step-Down Mode
Figure Maximum Switch Current RLIM Step-Up Mode
1100 1000 WITH 500µH VOUT
QUIESCENT CURRENT
SWITCH CURRENT
SUPPLY CURRENT
RLIM WITH 250µH VOUT
SWITCH CURRENT
TEMPERATURE
Figure Maximum Switch Current RLIM Step-Down Mode
Figure Supply Current Switch Current
Figure Quiescent Current Temperature
OSCILLATOR FREQUENCY
34.5
TEMPERATURE
SWITCH TIME
TEMPERATURE
DUTY CYCLE
33.5 32.5 31.5 30.5 TEMPERATURE
Figure Oscillator Frequency Temperature
Figure Duty Cycle Temperature
Figure Switch Time Temperature
REV.
ADP1108
0.58 0.53
(SAT) Volts
1.15 (SAT) 0.65A
(SAT) Volts
0.48 (SAT) 0.65A 0.43
1.05
0.38
0.33
0.95
0.28
TEMPERATURE
TEMPERATURE
Figure Switch Saturation Voltage Step-Up Mode Temperature
THEORY OPERATION
Figure Switch Saturation Voltage Step-Down Mode Temperature
ADP1108 flexible, power Switch Mode Power Supply (SMPS) controller. regulated output voltage greater than input voltage (boost step-up mode) less than input (buck step-down mode). This device uses gated-oscillator technique provide very high performance with quiescent current. functional block diagram ADP1108 shown front page. internal 1.245 reference connected input comparator, while other input externally connected (via pin) feedback network connected regulated output. When voltage falls below 1.245 oscillator turns driver amplifier provides base drive internal power switch, switching action raises output voltage. When voltage exceeds 1.245 oscillator shut off. While oscillator off, ADP1108 quiescent current only comparator includes small amount hysteresis, which ensures loop stability without requiring external components frequency compensation. maximum current internal power switch connecting resistor between ILIM pin. When maximum current exceeded, switch turned OFF. current limit circuitry time delay about external resistor used, connect ILIM VIN. Further information ILIM included Limiting Switch Current section this data sheet. ADP1108 internal oscillator provides times, which ideal applications where ratio between VOUT roughly factor three (such generating from input). µs/17 ratio permits continuous mode operation such cases, which increases available output power. uncommitted gain block ADP1108 connected low-battery detector. inverting input gain block internally connected 1.245 reference. noninverting input available pin. resistor divider, connected between with junction connected pin, causes output when battery point exceeded. output open collector transistor that sink
ADP1108 provides external connections both collector emitter internal power switch, which permits both step-up step-down modes operation. step-up mode, emitter (Pin SW2) connected collector (Pin SW1) drives inductor. step-down mode, emitter drives inductor while collector connected VIN. output voltage ADP1108 with external resistors. Three fixed-voltage models also available: ADP11083.3 (+3.3 ADP1108-5 ADP1108-12 (+12 fixed-voltage models identical ADP1108, except that laser-trimmed voltage-setting resistors included chip. fixed-voltage models ADP1108, simply connect feedback (Pin directly output voltage.
COMPONENT SELECTION General Notes Inductor Selection
When ADP1108 internal power switch turns current begins flow inductor. Energy stored inductor core while switch this stored energy then transferred load when switch turns off. Both collector emitter switch transistor accessible ADP1108, output voltage higher, lower, opposite polarity than input voltage. specify inductor ADP1108, proper values inductance, saturation current, resistance must determined. This process difficult, specific equations each circuit configuration provided this data sheet. general terms, however, inductance value must enough store required amount energy (when both input voltage switch time minimum) high enough that inductor will saturate when both switch time their maximum values. inductor must also store enough energy supply load, without saturating. Finally, resistance inductor should low, that excessive power will wasted heating windings. most ADP1108 applications, inductor with saturation current rating resistance suitable. Ferrite core inductors that meet these specifications available small, surfacemount packages. minimize Electro-Magnetic Interference (EMI), toroid core type inductor recommended. core inductors lower cost alternative problem.
REV.
ADP1108
Calculating Inductor Value
each switching cycle, inductor must supply:
=16.6
Selecting proper inductor value simple three-step process: Define operating parameters: minimum input voltage, maximum input voltage, output voltage output current. Select appropriate conversion topology (step-up, stepdown inverting). Calculate inductor value, using equations following sections.
Inductor Selection-Step-Up Converter
required inductor power fairly this example, peak current also low. Assuming peak current starting point, Equation rearranged recommend inductor value:
L(MAX
step-up boost converter (Figure 15), inductor must store enough power make difference between input voltage output voltage. inductor power calculated from equation:
IOUT
Substituting standard inductor value with resistance, will produce peak switch current
PEAK
-1.0
(Equation
where diode forward voltage 1N5818 Schottky). Energy only stored inductor while ADP1108 switch energy stored inductor each switching cycle must equal greater than:
Once peak current known, inductor energy calculated from Equation
(605 =18.3
(Equation
order ADP1108 regulate output voltage. When internal power switch turns current flow inductor increases rate
(Equation
where henrys switch equivalent resistance (typically +25°C) resistance inductor. voltage drop across switch small compared VIN, simpler equation used:
inductor energy 18.3 greater than PL/fOSC requirement 16.6 inductor will work this application. substituting other inductor values into same equations, optimum inductor value selected. When selecting inductor, peak current must exceed maximum switch current calculated peak current greater than either ADP3000 should considered external power transistor used. peak current must evaluated both minimum maximum values input voltage. switch current high when minimum, limit exceeded maximum value VIN. this case, current limit feature ADP1108 used limit switch current. Simply select resistor (using Figure that will limit maximum switch current IPEAK value calculated minimum value VIN. This will improve efficiency producing constant IPEAK increases. Limiting Switch Current section this data sheet more information. Note that switch current limit feature does protect circuit output shorted ground. this case, current limited only resistance inductor forward voltage diode.
Inductor Selection-Step-Down Converter
(Equation
Replacing above equation with time ADP1108 typical) will define peak current given inductor value input voltage. this point, inductor energy calculated follows:
2PEAK
(Equation
previously mentioned, must greater than PL/fOSC ADP1108 deliver necessary power load. best efficiency, peak current should limited less. Higher switch currents will reduce efficiency because increased saturation voltage switch. High peak current also increases output ripple. general rule, keep peak current possible minimize losses switch, inductor diode. practice, inductor value easily selected using equations above. example, consider supply that will generate from battery, assuming end-of-life voltage. inductor power required from Equation
0.5V
step-down mode operation shown Figure Unlike step-up mode, ADP1108's power switch does saturate when operating step-down mode. Therefore, switch current should limited this mode. input voltage will vary over wide range, ILIM used limit maximum switch current. Higher switch current possible adding external switching transistor, shown Figure first step selecting step-down inductor calculate peak switch current follows:
PEAK IOUT
(Equation REV.
ADP1108
where: duty cycle (0.7 ADP1108) voltage drop across switch diode drop (0.5 1N5818) IOUT output current VOUT output voltage minimum input voltage previously mentioned, switch voltage higher stepdown mode than step-up mode. function switch current therefore function VIN, time VOUT. most applications, value recommended. inductor value calculated:
IN(MIN PEAK
where: 0.65 (DC) 0.75 example, assume that output generated from +4.5 +5.5 source. power inductor calculated from Equation
5V|+ 0.5V (100
During each switching cycle, inductor must supply following energy:
28.9
Using standard inductor value with resistance will produce peak switch current (Equation
PEAK 4.5V 0.75 0.65
-0.95
where: switch time input voltage will vary (such application that must operate from source), RLIM resistor should selected from Figure RLIM resistor will keep switch current constant input voltage rises. Note that there separate RLIM values step-up step-down modes operation. example, assume that required from source. Deriving peak current from Equation yields:
PEAK
Once peak current known, inductor energy calculated from Equation
(568 35.5
inductor energy 35.5 greater than PL/fOSC requirement 28.9 inductor will work this application. avoid exceeding maximum switch current when input voltage +5.5 RLIM resistor should specified. Referring Figure value appropriate this application.
Capacitor Selection
peak current than inserted into Equation calculate inductor value:
optimum performance, ADP1108's output capacitor must carefully selected. Choosing inappropriate capacitor result efficiency and/or high output ripple. Ordinary aluminum electrolytic capacitors inexpensive, often have poor Equivalent Series Resistance (ESR) Equivalent Series Inductance (ESL). aluminum capacitors, specifically designed switch mode converter applications, also available, these better choice than general purpose devices. Even better performance achieved with tantalum capacitors, although their cost higher. Very values achieved using OS-CON* capacitors (Sanyo Corporation, Diego, CA). These devices fairly small, available with tape-and-reel packaging, have very ESR. effects capacitor selection output ripple demonstrated Figures These figures show output same ADP1108 converter, which evaluated with three different output capacitors. each case, peak switch current capacitor value Figure shows Panasonic HF-series* radial aluminum electrolytic. When switch turns off, output voltage jumps about then decays inductor discharges into capacitor. rise voltage indicates about 0.18 Figure aluminum electrolytic been replaced Sprague 593D-series* tantalum device. this case output jumps about which indicates 0.07 Figure shows OS-CON series capacitor same circuit, only 0.02
*All trademarks property their respective holders.
Since standard value, next lower standard value would specified. avoid exceeding maximum switch current when input voltage RLIM resistor should specified. Using Figure value will limit switch current
Inductor Selection-Positive-to-Negative Converter
configuration positive-to-negative converter using ADP1108 shown Figure with step-up converter, output power inverting circuit must supplied inductor. required inductor power derived from formula:
IOUT
(Equation
ADP1108 power switch does saturate positive-tonegative mode. voltage drop across switch modeled 0.75 base-emitter diode series with 0.65 resistor. When switch turns inductor current will rise rate determined
(Equation
REV.
ADP1108
less than similar device, BAT54, available SOT-23 package. Even lower leakage, range, obtained with 1N4148 signal diode. General purpose rectifiers, such 1N4001, suitable ADP1108 circuits. These devices, which have turn-on times more, slow switching power supply applications. Using such diode "just started" will result wasted time effort. Even ADP1108 circuit appears function with 1N4001, resulting performance will indicative circuit performance when correct diode used.
Circuit Operation, Step-Up (Boost) Mode
COUT =100 500mA
0.18
50mV
Figure Aluminum Electrolytic
boost mode, ADP1108 produces output voltage higher than input voltage. example, generated from logic power supply derived from alkaline cells Figure shows ADP1108 configured step-up operation. collector internal power switch connected output side inductor, while emitter connected GND. When switch turns pulled near ground. This action forces voltage across equal VCE(SAT), current begins flow through This current reaches final value (ignoring second-order effects)
PEAK (SAT
COUT =100µF, 500mA 0.07
50mV
Figure Tantalum Electrolytic
where ADP1108 switch's "on" time.
VOUT
COUT =100 500mA 0.02
ILIM
ADP1108
50mV
Figure OS-CON Capacitor
Figure Step-Up Mode Operation
output ripple important, user should consider using ADP3000. This device switches kHz, which simplifies design output filter. Consult ADP3000 data sheet additional details.
DIODE SELECTION
When switch turns off, magnetic field collapses. polarity across inductor changes, current begins flow through into load output voltage driven above input voltage. output voltage back ADP1108 resistors When voltage falls below 1.245 turns "on" again cycle repeats. output voltage therefore formula:
1.245
specifying diode, consideration must given speed, forward voltage drop reverse leakage current. When ADP1108 switch turns off, diode must turn rapidly high efficiency maintained. Schottky rectifiers, well fast signal diodes such 1N4148, appropriate. forward voltage diode represents power that delivered load, must also minimized. Again, Schottky diodes recommended. Leakage current especially important low-current applications, where leakage significant percentage total quiescent current. most circuits, 1N5818 suitable companion ADP1108. This diode leakage fast turn-on turn-off times. surface mount version, MBRS130T3, also available. switch currents less, Schottky diode such BAT85 provides leakage
circuit Figure shows direct current path from VOUT, inductor Therefore, boost converter protected output short circuited ground.
Circuit Operation, Step-Down (Buck) Mode
ADP1108's step-down mode used produce output voltage lower than input voltage. example, output four NiCd cells (+4.8 converted logic supply. typical configuration step-down operation ADP1108 shown Figure this case, collector internal power switch connected emitter drives inductor. REV.
ADP1108
When switch turns pulled toward VIN. This forces voltage across equal (VIN VCE) VOUT, causes current flow This current reaches final value
PEAK
Increasing Output Current Step-Down Regulator
where ADP1108 switch's "on" time.
RLIM
ILIM
VOUT 1N5818
ADP1108
Unlike boost configuration, ADP1108's internal power switch saturated when operating step-down mode. conservative value voltage across switch step-down mode This results high power dissipation within ADP1108 when high peak current required. increase output current, external switch added (Figure 18). this circuit, ADP1108 provides base drive through while ensures that turns rapidly. ADP1108's internal current limiting function will work this circuit, provided this purpose. With value shown, limits current addition reducing power dissipation ADP1108, this circuit also reduces switch voltage. When selecting inductor value circuit Figure switch voltage calculated from formula:
Q1(SAT
0.22 ZETEX ZTX749
Figure Step-Down Mode Operation
When switch turns off, magnetic field collapses. polarity across inductor changes switch side inductor driven below ground. Schottky diode then turns current flows into load. Notice that Absolute Maximum Rating ADP1108's below ground. avoid exceeding this limit, must Schottky diode. silicon diode used which will cause potentially damaging power dissipation within ADP1108. output voltage buck regulator back ADP1108's resistors When voltage falls below 1.245 internal power switch turns "on" again cycle repeats. output voltage formula:
1.245
6.5V
1N5818 5VOUT 200mA 6.5V 500mA
ILIM
SENSE
ADP1108-5
COILTRONICS CTX100-4
Figure High Current Step-Down Operation
Positive-to-Negative Conversion
When operating ADP1108 step-down mode, output voltage impressed across internal power switch's emitterbase junction while switch off. protect switch, output voltage should limited less. higher output voltage required, Schottky diode should placed series with SW2, shown Figure
RLIM
ADP1108 convert positive input voltage negative output voltage, shown Figure This circuit essentially identical step-down application Figure except that "output" side inductor connected power ground. When ADP1108's internal power switch turns off, current flowing inductor forces output VOUT) negative potential. ADP1108 will continue turn switch until 1.245 above pin, output voltage determined formula:
1.245
ILIM
VOUT 1N5818
ADP1108
ILIM
ADP1108
1N5818 -VOUT
Figure Step-Down Model, VOUT
input voltage ADP1108 varies over wide range, current limiting resistor required. particular circuit requires high peak inductor current with minimum input supply voltage, then peak current exceed switch maximum rating and/or saturate inductor when supply voltage maximum value. Limiting Switch Current section this data sheet specific recommendations. REV.
Figure Positive-to-Negative Converter
design criteria step-down application also apply positive-to-negative converter. output voltage should limited |6.2 unless diode inserted series with (see Figure 17). Also, must again Schottky diode prevent excessive power dissipation ADP1108.
ADP1108
Negative-to-Positive Conversion
circuit Figure converts negative input voltage positive output voltage. Operation this circuit configuration similar step-up topology Figure except that current through feedback resistor level-shifted below ground transistor. voltage across (VOUT-VBEQ1). However, diode level-shifts base about below ground, thereby cancelling addition also reduces circuit's output voltage sensitivity temperature, which would otherwise dominated contribution output voltage this circuit determined formula:
=1.245V
50µs
VOUT 100mA
120µH RLIM
200mA
2.23V
Figure (ILIM Operation, RLIM
50µs
Unlike positive step-up converter, negative-to-positive converter's output voltage either higher lower than input voltage.
RLIM
VOUT 100mA 120µH RLIM 2.23V
1N5818 2N3906
POSITIVE OUTPUT
ILIM
200mA
1N4148
ADP1108
Figure (ILIM Operation, RLIM
NEGATIVE INPUT
Figure Negative-to-Positive Converter
Limiting Switch Current
ADP1108's RLIM permits switch current limited with single resistor. This current limiting action occurs pulse pulse basis. This feature allows input voltage vary over wide range, without saturating inductor exceeding maximum switch rating. example, particular design require peak switch current with input. rises however, switch current will exceed ADP1108 limits switch current thereby protects switch, output ripple will increase. Selecting proper resistor will limit switch current even increases. relationship between RLIM maximum switch current shown Figures ILIM feature also valuable controlling inductor current when ADP1108 goes into continuous-conduction mode. This occurs step-up mode when following condition met:
DIODE
internal structure ILIM circuit shown Figure ADP1108's internal power switch, which paralleled sense transistor relative sizes scaled that 0.5% IQ1. Current flows through internal resistor through RLIM resistor. These resistors parallel base-emitter junction oscillatordisable transistor, When voltage across RLIM exceeds turns terminates output pulse. only internal resistor used (i.e. ILIM connected directly VIN), maximum switch current will
RLIM (EXTERNAL) DRIVER OSCILLATOR ILIM
ADP1108
(INTERNAL)
Figure ADP1108 Current Limit Operation
where ADP1108's duty cycle. When this relationship exists, inductor current does zero during time that switch OFF. When switch turns next cycle, inductor current begins ramp from residual level. switch time remains constant, inductor current will increase high level (see Figure 21). This increases output ripple require larger inductor capacitor. controlling switch current with ILIM resistor, output ripple current maintained design values. Figure illustrates action ILIM circuit.
delay through current limiting circuit approximately switch time reduced less than accuracy current trip-point reduced. Attempting program switch time less will produce spurious responses switch time. However, ADP1108 will still provide properly regulated output voltage.
-10-
REV.
ADP1108
PROGRAMMING GAIN BLOCK
gain block ADP1108 used battery detector, error amplifier linear post regulator. gain block consists with inputs open-collector output. inverting input internally connected ADP1108's 1.245 reference, while noninverting input available Pin. output transistor will sink about Figure shows gain block configured low-battery monitor. Resistors should high values reduce quiescent current, high that bias current input causes large errors. value good compromise. value then calculated from formula:
LOBATT 1.245 1.245
VBAT
ADP1108
1.245V
PROCESSOR
1.6M
Figure 24b. Adding Hysteresis Battery Detector
6.5V
0.22
ZETEX ZTX749
1N5818 5VOUT 200mA 6.5V 500mA
where VLOBATT desired battery trip point. Since gain block output open-collector NPN, pull-up resistor should connected positive logic power supply.
ILIM
SENSE
ADP1108-5
COILTRONICS CTX100-4
VBAT
ADP1108
1.245V
PROCESSOR
Figure Step-Down Converter
6.5V
-1.245V 37.7µA BATTERY TRIP POINT
ILIM
ADP1108-5
Figure 24a. Setting Battery Detector Trip Point
SENSE
circuit Figure produce multiple pulses when approaching trip point, noise coupled into input. prevent multiple interrupts digital logic, hysteresis added circuit (Figure 24b). Resistor with value provides hysteresis. addition will change trip point slightly, value will
LOBATT 1.245 1.245 1.245
300µH MBRS130T3
330µF OUTPUT 150mA
COILTRONICS CTX300-4
Figure Positive Converter
where logic power supply voltage, pull-up resistor creates hysteresis.
REV.
-11-
ADP1108
OUTLINE DIMENSIONS
Dimensions shown inches (mm).
8-Lead Plastic (N-8)
0.430 (10.92) 0.348 (8.84)
0.280 (7.11) 0.240 (6.10)
0.210 (5.33) 0.160 (4.06) 0.115 (2.93)
0.060 (1.52) 0.015 (0.38) 0.130 (3.30) SEATING PLANE
0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93)
0.022 (0.558) 0.100 0.070 (1.77) 0.014 (0.356) (2.54) 0.045 (1.15)
0.015 (0.381) 0.008 (0.204)
8-Lead SOIC (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)
-12-
REV.
PRINTED U.S.A.
C2992-12-2/97
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