28V, 1.5A, 1.4MHz Step-Down DC/DC Converter SOT23-6 FEATURES Wide
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ACT4088
28V, 1.5A, 1.4MHz Step-Down DC/DC Converter SOT23-6 FEATURES
Wide 4.5V Input Voltage Range 1.5A Output Current (12VIN 5VOUT) Output Adjustable Down 0.81V Internal Power MOSFET Efficiency Stable with Ceramic Output Capacitors Fixed 1.4MHz Operating Frequency Internal Soft-Start Function Over Current Protection with Hiccup-Mode Thermal Shutdown Available SOT23-6 Package
GENERAL DESCRIPTION
ACT4088 current-mode step-down DC/DC converter that supplies 1.5A into from input. 1.4MHz switching frequency allows tiny external components, internal loop compensation provides simple, stable power supplies with minimum external components. Optimized with ceramic input output capacitors, ACT4088 provides very compact 1.5A power supply space constrained mobile consumer applications. ACT4088 operates over wide input voltage range utilizes current-mode operation provide excellent line load transient response while requiring external compensation components. Fault protection includes cycle-by-cycle current limiting, frequency fold-back, hiccup mode, thermal shutdown. Internal soft-start provides controlled startup with overshoot, even light loads. ACT4088 available tiny SOT23-6 package requires very external components.
APPLICATIONS
Monitors Portable DVDs, Headphones, Players, etc. Car-Powered Battery-Powered Equipment Set-Top Boxes Telecom Power Supplies Cable Modems Routers
TYPICAL APPLICATION CIRCUIT
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ACT4088
PrA, 24-Jul-07
ORDERING INFORMATION
PART NUMBER
ACT4088US-T
TEMPERATURE RANGE
-40°C 85°C
PACKAGE
SOT23-6
PINS
PACKING TAPE REEL
CONFIGURATION
SOT23-6
DESCRIPTIONS
NUMBER
NAME
DESCRIPTION
Switch Output. Connect this switching inductor. Power supply input. Bypass this with 10µF ceramic capacitor placed close possible. Enable Input. pulled with current, contains precise 1.24V logic threshold. Drive this logic-high leave unconnected enable Drive logic-low disable enter micro-power shutdown mode. Feedback Input. voltage this regulated 0.81V. Connect center point resistive voltage-divider between output voltage. Ground Heat sink. Connect this large, uncovered copper area best heat dissipation. Bootstrap. This acts power supply high-side switch's gate driver. Connect 2.2nF capacitor between this
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ACT4088
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ABSOLUTE MAXIMUM RATINGS
PARAMETER
Supply Voltage Voltage Voltage Voltage Continuous Current Junction Ambient Thermal Resistance (JA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, sec)
VALUE
-0.3 -0.3 Internally Limited
UNIT
°C/W
exceed these limits prevent damage device. Exposure absolute maximum rating conditions long periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN 12V, 25°C, unless otherwise specified.)
PARAMETER
Input Voltage Under Voltage Lockout Voltage Under Voltage Lockout Hysteresis Feedback Voltage Frequency Foldback Threshold High-side Switch Resistance Low-side Switch Resistance Leakage Current Limit Switching Frequency Foldback Switching Frequency Maximum Duty Cycle Minimum On-Time Threshold Voltage Hysteresis Internal Pull-up Current Supply Current Shutdown Supply Current Operation Thermal Shutdown Temperature Thermal Shutdown Hysteresis
SYMBOL
VUVLO
TEST CONDITIONS
VOUT 3.3V, ILOAD 1.5A Input Voltage Rising 4.75V 20V, VCOMP 1.5V
4.49
UNIT
0.79
0.81
0.83
RONH RONH ILfSW DMAX 0.6V 12V, VOUT
0.300 Rising Rising 1.12 1.24 1.0V 1.36
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ACT4088
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TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit Figure 12V, 4.7µH, 10µF, 22µF, +25°C, unless otherwise specified.)
Efficiency Load Current
ACT4088-001
Efficiency Load Current
ACT4088-002
Efficiency
Efficiency
VOUT
VOUT 3.3V
Load Current
Load Current
Voltage Temperature
1.60 ACT4088-003
Oscillator Frequency Temperature
ACT4088-004
Oscillator Frequency (MHz)
Voltage (mV)
1.50
1.40
1.30
1.20
Temperature (°C)
Temperature (°C)
Peak Current Limit Duty Cycle Quiescent Supply Current (µA)
ACT4088-005
Shutdown Current Input Voltage
ACT4088-006
Peak Current Limit
Pull-up Current
Duty Cycle
Input Voltage
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ACT4088
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TYPICAL PERFORMANCE CHARACTERISTICS CONT'D
(Circuit Figure 12V, 4.7µH, 10µF, 22µF, +25°C, unless otherwise specified.)
Load Transient Response
ACT4088-007 ILOAD 200mA 800mA
Load Transient Response
ACT4088-008 ILOAD 200mA 1.5A
CH1: VOUT, 50mV/div CH2: ILOAD, 500mA/div TIME: 100µs/div
CH1: VOUT, 50mV/div CH2: ILOAD, 500mA/div TIME: 100µs/div
Start-up Waveforms
ACT4088-009 ILOAD ILOAD
Start-up Waveforms
ACT4088-010
CH1: VOUT, 2V/div CH2: 10V/div CH3: 1A/div TIME: 200µs/div
CH1: VEN, 2V/div CH2: VOUT, 2V/div CH3: 10V/div CH4: 1A/div TIME: 400µs/div
Steady State Switching Waveforms
ACT4088-011 ILOAD
Hiccup Mode Switching Waveforms
ACT4088-012
CH1: VOUT, 50mV/div, COUPLED) CH2: 10V/div CH3: 500mA/div TIME: 400ns/div CH1: VOUT, 100mV/div, COUPLED) CH2: 1A/div TIME: 1ms/div
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ACT4088
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FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL DESCRIPTION
ACT4088 current-mode step-down DC/DC converter that provides excellent transient response with extra external compensation components. This device contains internal, low-resistance, high-voltage power MOSFET, operates high 1.4MHz operating frequency ensure compact, high-efficiency design with excellent performance.
setting ACT4088's transient response ensuring stability. most applications, choosing RFB1 49.9k provides good results. applications with output voltages 1.8V lower, larger RFB1 value such 80.6k. Once RFB1 chosen, following equation choose RFB2:
RFB1 VOUT 0.81V
Setting Output Voltage
external voltage divider used output voltage, well provide known impedance from VOUT compensation purposes. Connect resistor from output ensure stable compensation, select bottom resistor provide desired regulation voltage. Figure Output Voltage Setting
Selecting Inductor
ACT4088 optimized with 4.7µH inductor. When choosing inductor, choose with resistance less than 250m current rating that typically higher than maximum load current. During typical operation, inductor maintains continuous current output load. inductor current ripple that dependent inductance value. Higher inductance reduces peak-to-peak ripple current. trade high inductance value increase inductor core size series resistance, reduction current handling capability. efficiency light loads (such less than 100mA) critical application, larger inductor recommended.
feedback resistor (RFB1) interacts with internal compensation network, plays important
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ACT4088
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Rectifier Diode
Schottky diode rectifier conduct current when High-Side Power Switch off. Schottky diode must have current rating higher than maximum output current reverse voltage rating higher than maximum input voltage (see Figure
Shutdown Control
ACT4088 enable provides several features adjusting sequencing power supply. internal current source pull-up, precision 1.24V comparator with hysteresis. With these components, user flexibility using digital on/off control pulling down current source with external open-drain transistor. voltage internally clamped sequenced power supply tying through resistor output another power supply. will enabled when voltage exceeds 1.24V, resistor divider used adjust turn-on threshold. always-on converter floating pulling desired voltage with high value (1M) external resistor. internally clamped will dissipate power external resistor attempts pull above clamp voltage. Line UVLO. desired, achieve UVLO voltage that higher than internal UVLO, external resistor divider from used disable ACT4088 until higher input voltage achieved. example, useful converter with output start with 4.2V input voltage, output cannot reach regulation. enable ACT4088 when input voltage reaches 12V, 9k/1k resistor divider from connected pin. Both precision 1.2V threshold 80mV hysteresis multiplied resistor ratio, providing proportional 6.67% hysteresis startup threshold. example enable threshold, turn threshold would 11.2V. Power supply sequencing. connecting small capacitor from GND, current source 1.24V threshold provide stable predictable delay between startup multiple power supplies. example, startup delay roughly 10mS provided using 150nF, roughly 20mS using 330nF. current source active anytime input supply applied, disabling resetting delay requires external open-drain pull-down device reset capacitor hold shutdown.
Selecting Input Capacitor
best performance choose ceramic type capacitor with dielectrics their small temperature coefficients. However, tantalum electrolytic types also used, provided that ripple current rating higher than output current. most applications, 10µF capacitor sufficient. input capacitor should placed close pins with shortest possible traces. case tantalum electrolytic types, connect small parallel 0.1µF ceramic capacitor right next
Selecting Output Capacitor
22µF ceramic capacitor with dielectric provides best results over wide range applications. output capacitor also needs have keep output voltage ripple. output ripple voltage
VRIPPLE IOUTMAX RIPPLE RESR
LCOUT
where IOUTMAX maximum output current, KRIPPLE ripple factor (typically 30%), RESR resistance output capacitor, switching frequency, inductor value, COUT output capacitance. case ceramic output capacitors, RESR very small does contribute ripple. case tantalum electrolytic type, ripple dominated RESR multiplied ripple current. that case, output capacitor chosen have sufficiently ESR, typically choose capacitor with less than ESR.
External Bootstrap Diode
external bootstrap diode Figure recommended input voltage less than 5.5V there system rail available. This diode helps strengthen gate drive lower input voltages, resulting lower on-resistance higher efficiency. cost diodes, such 1N4148 BAT54, suitable this application.
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ACT4088
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Soft-Start
ACT4088 provides internal soft-start feature, which ramps output voltage output current from full value over milliseconds. This feature prevents output voltage overshoot light loads well prevent large inrush currents upon startup. soft-start circuitry internally reset anytime disabled using pin, well reaches hiccup mode thermal shutdown. these cases, soft-start provides smooth, controlled restart after fault removed.
Frequency Foldback
voltage monitored comparator detect extreme output overload condition. voltage falls below 0.3V, internal oscillator slows decreased frequency 467kHz, nominal value. This prevents inductor current from rising excessively during dead-short condition, potentially resulting inductor saturation.
Figure ACT4088 Typical 5V/1.5A Output Application
Optional Connection: 5.5V VOUT 5.5V 1N4148 (Optional) 22nF
10µF
ACT4088
B240A RFB2 9.53k
4.7µH 22µF RFB1 49.9k VOUT
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ACT4088
PrA, 24-Jul-07 Figure ACT4088 Optimized Minimal External Components
ACT4088 with provides excellent results across wide range external component combinations. circuit Figure used generate output from input utilizing smaller (i.e. lower-cost) output capacitor while maintaining good performance.
Figure Circuit Figure (ILOAD 150mA 850mA)
ACT4088-013 Circuit Figure ILOAD 150mA 850mA
Figure Circuit Figure (ILOAD
ACT4088-014 Circuit Figure ILOAD
CH1: ILOAD, 500mA/div CH2: VOUT, 100mV/div Coupled) TIME: 200µs/div
CH1: 10V/div CH2: VOUT, 20mV/div Coupled) TIME: 400ns/div
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ACT4088
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Hiccup Mode
ACT4088 transitions from normal operation severe overload condition (the voltage falls below 0.3V), controller automatically enters "Hiccup Mode" provide maximum protection system. hiccup mode, stops switching, clears soft-start circuitry, then attempts restart. overload condition been removed, will start normally continue regulating. case sustained overload, however, will attempt regulate period time equal soft-start period (1.5ms). overload condition persists until this period, will begin another hiccup cycle. This hiccup-mode control scheme minimizes power dissipation during severe overload conditions, ensures that ACT4088 responds quickly instantaneous severe overload conditions while providing immunity false hiccups that occur with heavily loaded output.
Thermal Shutdown
ACT4088 automatically turns when junction temperature exceeds 160°C, reenables when junction temperature drops 10°C (typ).
Board Layout
high current paths should placed very close device with short, direct wide traces. input capacitor needs close possible pins. external feedback resistors should placed next pin. Keep switch node traces short away from feedback network shielded inductors.
Innovative Products. Active Solutions.
www.active-semi.com Copyright 2007 Active-Semi, Inc.
ACT4088
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PACKAGE OUTLINE
SOT23-6 PACKAGE OUTLINE DIMENSIONS
SYMBOL
DIMENSION MILLIMETERS
1.050 0.000 1.050 0.300 0.100 2.820 1.500 2.650
DIMENSION INCHES
0.041 0.000 0.041 0.012 0.004 0.111 0.059 0.104
1.250 0.100 1.150 0.500 0.200 3.020 1.700 2.950
0.049 0.004 0.045 0.020 0.008 0.119 0.067 0.116
0.950 1.800 2.000
0.037 0.071 0.079
0.700 0.300 0.600
0.028 0.012 0.024
Active-Semi, Inc. reserves right modify circuitry specifications without notice. Users should evaluate each product make sure that suitable their applications. Active-Semi products intended authorized critical components life-support devices systems. Active-Semi, Inc. does assume liability arising product circuit described this datasheet, does convey patent license. Active-Semi logo trademarks Active-Semi, Inc. more information this other products, contact sales@active-semi.com visit http://www.active-semi.com. other inquiries, please send 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044,
Innovative Products. Active Solutions.
www.active-semi.com Copyright 2007 Active-Semi, Inc.
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