HIGH PERFORMANCE CURRENT MODE CONTROLLERS Start-Up Operating Curr
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
Start-Up Operating Current Automatic Feed Forward Compensation Current Mode Operating Frequency 500kHz Trimmed Oscillator Discharge Current Precise Duty Cycle Control Latching Cycle-By-Cycle Current Limiting Undervoltage Lockout with Hysteresis High Current Totem Pole Output GM384xA series high performance fixed-frequency current mode controllers designed off-Line DC-to-DC converter applications. They require minimal external components precisely tailor performance wide variety applications. These GM384xA's incluide trimmed oscillator precise duty cycle control, temperature-compensated reference, high gain error amplifier, current-sensing comparator, high-current totem pole output driving power MOSFET. On-chip protection features include undervoltage lockouts with hysteresis both input reference, cycle-by-cycle current limiting, programmable output deadtime, latch single pulse metering. this simple DIP-8 SOP-8 package! GM3842A GM3844A have UVLO thresholds (on)/10V(off); GM3843A GM3845A have UVLO thresholds 8.4V (on)/7.6V (off). GM3842A GM3843A operate within 100% duty cycle; GM3844A GM3845A operate within duty cycle. SIMPLIFIED BLOCK DIAGRAM
VREF OSCILLATOR
Error Amplifier
CONNECTIONS
COMP ISENSE
VREF OUTPUT
DIP-8, SOP-8 (TOP VIEW)
Compensation Feedback Current Sense
VREF OUTPUT Power Ground
SOP-14 (TOP VIEW)
5.0V REFERENCE
LOCKO
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
ABSOLUTE MAXIMUM RATINGS
PARAMETER
Supply Voltage (low impedance source) Output Current, Source Sink Input Voltage (analog inputs pins 2,3) Maximum Power Dissipation (TA=25°C) Error Output Sink Current Operating Junction Temperature Storage Temperature Range Lead Temperature (soldering sec.)
Note: Maximum Package Power Dissipation Limits must observed.
SYMBOL
ISINK(E.A) Tstg
VALUE
±1.0 -0.3 +5.5 +150 +150
UNITS
FUNCTIONS DESCRIPTION
FUNCTION COMP ISENSE RT/CT OUTPUT VREF DESCRIPTION
This Error Amplifier output made available loop compensation. This inverting input Error Amplifier. normally connected switching power supply output through resistor divider. voltage proportional inductor current connected this input. uses this information terminate output switch conduction. Oscillator frequency maximum Output duty cycle programmed connecting resistor VREF capacitor ground. Operation possible. This combined control circuitry power ground. This output directly drives gate power MOSFET. Peak currents sourced sunk this pin. This positive supply control integrated circuit (IC). This reference output. provides charging current capacitor resistor
through
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
ELECTRICAL CHARACTERISTICS
CHARACTERISTICS
Reference Section Reference Output Voltage Line Regulation Load Regulation Short Circuit Output Current Oscillator Section Oscillation Frequency Frequency Change with Voltage Oscillator Amplitude Error Amplifier Section Input Bias Current Input Voltage Open Loop Voltage Gain Power Supply Rejection Ratio Output Sink Current Output Source Current High Output Voltage Output Voltage Current Sense Section Gain Maximum Input Signal Supply Voltage Rejection Input Bias Current Output Section Output Voltage ISINK ISINK ISINK ISINK TJ=25°C, (Note TJ=25°C, (Note 0.08 13.5 VI(MAX) IBIAS (Note VPIN1 (Note (Note1) VPIN3 2.85 -3.0 3.15 IBIAS (E.A) AVOL PSRP ISINK ISOURCE VPIN1 2.5V VPIN2 2.7V, VPIN1 1.1V VPIN2 2.3V, VPIN1 VPIN2 2.3V, RL=15k VPIN2 2.7V, RL=15k Pin8 -0.5 -0.1 -1.0 -2.0 2.58 V(OSC) TJ=25°C (peak peak) 0.05 VREF VREF VREF TJ=25°C, REF=1mA 20mA TA=25°C -100 -180
*VCC=15V, CT=3.3nF, RT=10k, unless otherwise specified
TEST CONDITIONS UNIT
SYMBOL
High Output Voltage Rise Time Fall Time Undervoltage Lockout Section Start Threshold
GM3842A, GM3844A VTH(ST) GM3843A, GM3845A GM3842A, GM3844A VOPR(MIN) GM3843A, GM3845A
14.5
16.0
17.5 11.5
Minimum Operating Voltage (after turn Section Maximum Duty Cycle Minimum Duty Cycle Total Standby Current Start-Up Current Operating Supply Current Zener Voltage
GM3842A, GM3843A D(MAX) D(MIN) GM3844A, GM3845A
ICC(OPR) VPIN3 VPIN2
0.17
Adjust above Startup threshold before setting Note1: Parameter measured trip point latch with VPIN2 Note2: Gain defined A=VPIN1 VPIN3 VPIN3 0.8V Note3: These parameters, although guaranteed, 100% tested production Revision 2002 www.gammamicro.com
GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
REPRESENTATIVE BLOCK DIAGRAM
Vref 2.5V
Reference Regulator
UVLO
Internal Bias 3.6V Oscillator
Vref UVLO
Output Power Ground Latch Current Sense Comparator Current Sense Input
Error Amplifier
1.0mA
Voltage Feedback Input Output Compensation
1.0V
Positive True Logic
Sink Only
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
OPERATING DESCRIPTION
GM3842A, GM3843A, GM3844A GM3845A high performance, fixed frequency, current mode controllers. They designed off-line DC-to- converter applications offering great versatility with minimal external components. representative block diagram shown page Oscillator oscillator frequency determined values timing components Capacitor charged from reference through resistor approximately discharged internal current sink. discharges, oscillator generates internal blanking pulse that holds center input gate high. This causes output state, produces controlled amount output deadtime. Many different values will give same oscillator frequency, only combination will yield specific output deadtime given frequency. oscillator thresholds temperature-compensated; discharge current trimmed guaranteed within ±10% 25°C. Thiw minimizes variations oscillator frequency maximum output duty cycle. many noise sensitive applications desirable frequency-lock converter applying clock signal circuit shown Figure best locking results, free-running oscillator frequency about less than clock frequency. method multi unit synchronization shown Figure very accurate output duty cycle clamping tweaking clock waveform. Error Amplfier Output (Pin allows external loop compensation. output voltage offset diode drops (1.4 divided three before connecting inverting input Current Sense Comparator. This assures that drive pulses appear Output (Pin when lowest state (VOL). This happens when power supply operating load removed, beginning soft- start interval (Figures Error minimum feedback resistance limited amplifier's source current (0.5 required output voltage (VOH) reach comparator's clamp level: RF(min)
(1.0 8800
Current Sense Comparator Latch GM384xA's operate current mode controller, whereby output switch conduction initiated oscillator terminated when peak inductor current reaches threshold level established Error Amplifier Output/Compensation (Pin1). error signal controls peak inductor current cycle-by-cycle. Current Sense Comparator Latch configuration assures that only single pulse appears Output during given oscillator cycle. inductor current converted voltage inserting groundreferenced sense resistor series with source output switch This voltage monitored Current Sense Input (Pin compared level derived from Error Output. peak inductor current under normal operating conditions controlled voltage where: V(Pin
Error Amplifier GM384xA's have fully compensated error amplifier with access both inverting input output, providing voltage gain (typical). noninverting input internally biased pinned out. converter output voltage typically divided down monitored inverting input. maximum input bias current -2.0 which cause output voltage error that equal product input bias current equivalent input divider source resistance.
When power supply output overloaded output voltage sensing lost, chip operation normal. these situations, Current Sense Comparator threshold will internally clamped maximum peak switch current Ipk(max) 1.0V
Revision 2002
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
designing high power switching regulator really want reduce internal clamp voltage, keep reasonable level power dissipation Adjusting internal clamp voltage very simple, shown Figure external diodes compensate internal diodes constant clamp voltage over temperature. Avoid much reduction Ipk(max) clamp voltage, will noise pickup erratic results. narrow spike leading edge current waveform often occurs cause power supply instability when output load light. This spike caused power transformer interwinding capacitance output rectifier recovery time. eliminate this problem adding filter Current Sense Input, with time constant similar spike's duration; Figure Undervoltage Lockout UVLO comparators GM384xA's assure that chips fully functional before output stage enabled. positive power supply terminal (VCC) reference output each have separate comparators. Each built-in hysteresis prevent erratic output behavior their thresholds reached. comparator upper lower thresholds V/10 GM3842A GM3844A, 8.4V/7.6V GM3843A GM3845A. Vref comparator upper lower thresholds 3.6V/3.4 large hysteresis startup current GM3842A GM3844A makes them ideal off-line converter applications where efficient bootstrap startup required. GM3843A GM3845A intended lower voltage DC-to-DC converter applications. zener connected shunt regulator form ground. purpose protect from excessive voltage that occur during system startup. minimum operating voltage GM3842A GM3844A 11V; GM3843A GM3845A 8.2V. typical rise fall time with load. Additional internal circuitry keeps output sinking mode whenever UVLO active. This eliminates need external pull-down resistor. SO-14 surface mount package provides separate pins (output supply) Power Ground. Proper implementation will significantly reduce switching transient noise levels imposed control circuitry. This very useful when reducing Ipk(max) clamp level. separate supply input gives added flexibility tweak drive voltage independent VCC. zener clamp typically connected this input when driving power MOSFETs systems where greater than 20V. Figure shows proper power control ground connections current-sensing power MOSFET application. Reference bandgap reference trimmed ±2.0% tolerance 25°C GM384xA's. primary purpose supply charging current oscillator timing capacitor. reference short circuit protection provide more than 20mA powering additional control system circuitry.
Output GM384xA's have single totem pole output stage that designed direct drive power MOSFETs. provides ±1.0 peak drive current
Design Considerations make your converter using wire-wrap plug-in prototype boards. High-frequency circuit layout techniques must observed prevent pulsewidth jitter. This usually caused excessive noise pick-up imposed Current Sense Voltage Feedback inputs. improve noice immunity lowering circuit impedances these points. layout should have ground plane with low-current signal high-current switch output grounds returning separate paths input filter capacitor. Ceramic bypass capacitors (0.1 connected directly VCC, Vref required, depending upon circuit layout, provide impedance path filtering high frequency noise. high-current loops should short possible heavy copper runs minimize radiated EMI. Error compensation circuitry converter output voltage divider should placed close possible GM384xA, possible from power switch other noisegenerating components.
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
Figure EXTERNAL CLOCK SYNCHRONIZATION
Vref
Internal Bias
External Sync Input 0.01 Oscillator
Error Amplifier
diode clamp required Sync amplitude large enough cause bottom side more than below ground.
Figure EXTERNAL DUTY CYCLE CLAMP MULTI-UNIT SYNCHRONIZATION
Internal Bias
Oscillator
5.0k
5.0k
5.0k
Error Amplifier
Additional GM384xA's
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
Figure ADJUSTABLE REDUCTION CLAMP LEVEL
Vref
Internal Bias Oscillator
1.0mA 1.0V Vclamp
Comp/Latch
Error Amplifier
Figure SOFT-START CIRCUIT
Vref
Internal Bias
Oscillator
1.0mA
1.0V
Error Amplifier
tsoft-start 3600C
Revision 2002
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
Figure ADJUSTABLE BUFFERED REDUCTION CLAMP LEVEL WITH SOFT-START
Vref
Internal Bias Oscillator
1.0mA 1.0V Vclamp
Comp/Latch
Error Amplifier
Figure CURRENT SENSING POWER MOSFET
Vref
SENSEFET
proper operation during over current conditions, reduction Ipk(max) clamp level must implemented. Refer Figures
1.0V
Comp/Latch
Power Ground Input Source Return 1/4W
Control Circuitry Ground
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
Figure CURRENT WAVEFROM SPIKE SUPPRESSION
Vref
addition filter will eliminate instability caused leading edge spike current waveform.
1.0V
Comp/Latch
ORDERING INFORMATION
PACKAGE SOP-8 GM3842A-S8 GM3843A-S8 GM3844A-S8 GM3845A-S8 SOP-14 GM3842A-S14 GM3843A-S14 GM3844A-S14 GM3845A-S14 DIP-8 GM3842A-D8 GM3843A-D8 GM3844A-D8 GM3845A-D8
PART GM3842A GM3843A GM3844A GM3845A
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
SOP-8 PACKAGE OUTLINE DIMENSIONS
SYMBOL
Dimensions Millimeters 1.45 1.35 0.306 0.153 4.81 3.84 5.84 1.27 0.45 1.75 0.25 1.55 0.506 0.253 5.01 4.04 6.24
Dimensions Inches 0.057 0.004 0.053 0.012 0.006 0.189 0.151 0.23 0.05 0.018 0.039 0.069 0.01 0.061 0.02 0.01 1.197 0.159 0.246
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
DIP-8 PACKAGE OUTLINE DIMENSIONS
SYMBOL
Dimensions Millimeters 3.71 0.51 0.36 1.374 0.204 7.42 2.34 0.56 1.674 0.404 7.82 2.74 4.31
Dimensions Inches 0.146 0.02 0.126 0.014 0.054 0.008 0.354 0.244 0.292 0.092 0.122 0.327 0.142 0.022 0.066 0.016 0.37 0.26 0.308 0.108 0.138 0.358 0.17
Revision 2002
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GM3842A,GM3843A,GM3844A,GM3845A
HIGH PERFORMANCE CURRENT MODE CONTROLLERS
SOP-14 PACKAGE OUTLINE DIMENSIONS
SYMBOL
Dimensions Millimeters 1.35 0.10 1.45 0.33 0.19 8.55 3.80 1.27 5.80 0.40 6.20 1.27 0.10 0.228 0.016 0.51 0.25 8.75 4.00 0.013 0.007 0.337 0.150 1.60 1.75 0.25 0.053 0.004
Dimensions Inches 0.063 0.057 0.020 0.010 0.344 0.157 0.050 0.244 0.050 0.004 0.069 0.010
NOTE PACKAGE BODY SIZES EXCLUDE MOLD FLASH GATE BURRS DIMENSION MEASURED GAGE PLANE TOLERANCE 0.10 UNLESS OTHERWISE SPECIFIED CONTROLLING DIMENSION MILLIMETER. CONVERTED INCH DIMENSIONS NECESSARILY EXACT. FOLLOWED FROM JEDEC MS-012
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