ACTIVE-SEMI ACT4082AUS-T

ACT4082A
Active-Semi
Rev0, 16-May-08
16V, 1.2A, 1.4MHz Step-Down DC/DC Converter in SOT23-6
FEATURES
GENERAL DESCRIPTION
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The ACT4082A is a current-mode step-down
DC/DC converter that supplies up to 1.2A into 5V
from a 12V input. 1.4MHz switching frequency allows the use of tiny external components, and internal loop compensation provides simple, stable
power supplies with a minimum of external components. Optimized for use with ceramic input and
output capacitors, the ACT4082A provides a very
compact 1.2A power supply for space constrained
mobile and consumer applications.
Wide 4.5V to 16V Input Voltage Range
1.2A Output Current (12VIN to 5VOUT)
Output Adjustable Down to 0.81V
0.3Ω Internal Power MOSFET
Up to 92% Efficiency
Stable with Low ESR Ceramic Output Capacitors
Fixed 1.4MHz Operating Frequency
Internal Soft-Start Function
The ACT4082A operates over a wide input voltage
range and utilizes current-mode operation to provide excellent line and load transient response
while requiring no external compensation components. Fault protection includes cycle-by-cycle current limiting, frequency fold-back, hiccup mode, and
thermal shutdown. Internal soft-start provides a
controlled startup with no overshoot, even at light
loads.
Over Current Protection with Hiccup-Mode
Thermal Shutdown
Available in a SOT23-6 Package
APPLICATIONS
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TFT LCD Monitors
The ACT4082A is available in a tiny SOT23-6 package and requires very few external components.
Portable DVDs, Headphones, MP3 Players, etc.
Car-Powered or Battery-Powered Equipment
Set-Top Boxes
Telecom Power Supplies
DSL and Cable Modems and Routers
TYPICAL APPLICATION CIRCUIT
VIN
4.5V to 16V
IN
BST
Active-Semi
ACT4082A SW
ON
OFF
VOUT
EN
FB
G
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ACT4082A
Active-Semi
Rev0, 16-May-08
ORDERING INFORMATION
PART NUMBER
TEMPERATURE RANGE
PACKAGE
PINS
PACKING
TOP MARK
ACT4082AUS-T
-40°C to 85°C
SOT23-6
6
TAPE & REEL
FMGD
PIN CONFIGURATION
SW
1
IN
2
EN
3
ACT4082A
6
BST
5
G
4
FB
SOT23-6
PIN DESCRIPTIONS
PIN NUMBER
PIN NAME
1
SW
2
IN
Power supply input. Bypass this pin with a 10µF ceramic capacitor to G, placed as
close to the IC as possible.
3
EN
Enable Input. EN is pulled up to 5V with a 2µA current, and contains a precise 1.24V
logic threshold. Drive this pin to a logic-high or leave unconnected to enable the IC.
Drive to a logic-low to disable the IC and enter micro-power shutdown mode.
4
FB
Feedback Input. The voltage at this pin is regulated to 0.81V. Connect to the center
point of a resistive voltage-divider between OUT and G to set the output voltage.
5
G
Ground and Heat sink. Connect this pin to a large, uncovered PCB copper area for
best heat dissipation.
6
BST
Bootstrap. This pin acts as the power supply for the high-side switch’s gate driver.
Connect a 22nF capacitor between this pin and SW.
Innovative PowerTM
PIN DESCRIPTION
Switch Output. Connect this pin to the switching end of the inductor.
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ACT4082A
Active-Semi
Rev0, 16-May-08
ABSOLUTE MAXIMUM RATINGSc
PARAMETER
VALUE
UNIT
-0.3 to 20
V
SW Voltage
-1 to VIN + 1
V
BST Voltage
VSW - 0.3 to VSW + 7
V
-0.3 to 6
V
Internally Limited
A
Junction to Ambient Thermal Resistance (θJA)
220
°C/W
Maximum Power Dissipation
0.5
W
Operating Junction Temperature
-40 to 150
°C
Storage Temperature
-55 to 150
°C
300
°C
IN Supply Voltage
EN, FB Voltage
Continuous SW Current
Lead Temperature (Soldering, 10 sec)
c: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may
affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TA = 25°C, unless otherwise specified.)
PARAMETER
Input Voltage
Under Voltage Lockout Voltage
SYMBOL
VIN
VUVLO
TEST CONDITIONS
VOUT = 3.3V, ILOAD = 0A to 1.2A
Input Voltage Rising
MIN
4.5
4
Under Voltage Lockout Hysteresis
Feedback Voltage
TYP
4.2
MAX
UNIT
16
V
4.49
V
250
VFB
4.75V ≤ VIN ≤ 16V, VCOMP = 1.5V
0.78
Frequency Foldback Threshold
0.81
mV
0.84
V
250
mV
High-side Switch On Resistance
RONH
0.300
Ω
Low-side Switch On Resistance
RONH
15
Ω
SW Leakage
VEN = 0, VSW = 0V
Current Limit
ILTM
Switching Frequency
fSW
Foldback Switching Frequency
Maximum Duty Cycle
DMAX
1
VIN = 12V, VOUT = 5V, or
EN = G, SW = G
10
1.8
1.1
1.4
µA
A
1.7
MHz
VFB = 0V, or FB = G
467
kHz
VFB = 0.6V
92
%
75
ns
Minimum On-Time
EN Threshold Voltage
EN Rising
EN Hysteresis
EN Rising
EN Internal Pull-up Current
1.12
1.24
1.36
V
100
mV
2
µA
Supply Current in Shutdown
VEN = 0V or EN = G
15
30
µA
Supply Current in Operation
VEN = 2V, VFB = 1.0V
1
2
mA
Thermal Shutdown Temperature
160
°C
Thermal Shutdown Hysteresis
10
°C
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ACT4082A
Active-Semi
Rev0, 16-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 2, VIN = 12V, L = 4.7µH, C1 = 10µF, C2 = 22µF, TA = +25°C, unless otherwise specified.)
Efficiency vs. Load Current
VIN = 16V
65
55
0.1
VIN = 16V
65
1
VOUT = 3.3V
50
10
0.1
1
10
Load Current (A)
Load Current (A)
FB Voltage vs. Temperature
Oscillator Frequency vs. Temperature
Oscillator Frequency (MHz)
816
812
808
804
ACT4082A-004
1.60
ACT4082A-003
820
FB Voltage (mV)
75
55
VOUT = 5V
50
1.50
1.40
1.30
1.20
800
-40
-20
0
20
40
60
80
100
-40
120
-20
0
20
60
40
80
100
Temperature (°C)
Temperature (°C)
Peak Current Limit vs. Duty Cycle
Shutdown Current vs. Input Voltage
2.0
Quiescent Supply Current (µA)
2.5
1.5
1.0
0.5
0.0
0
20
40
60
80
25
20
pp
Su
15
ent
urr
ly C
10
EN Pull-up Current
5
0
0
100
Duty Cycle
Innovative PowerTM
30
120
ACT4082A-006
ACT4082A-005
3.0
Peak Current Limit (A)
VIN = 12V
85
Efficiency (%)
Efficiency (%)
85
ACT4082A-002
VIN = 12V
75
95
ACT4082A-001
95
Efficiency vs. Load Current
4
8
12
16
20
Input Voltage (V)
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ACT4082A
Active-Semi
Rev0, 16-May-08
TYPICAL PERFORMANCE CHARACTERISTICS CONT’D
(Circuit of Figure 2, VIN = 12V, L = 4.7µH, C1 = 10µF, C2 = 22µF, TA = +25°C, unless otherwise specified.)
Load Transient Response
ACT4082A-008
CH1
ACT4082A-007
ILOAD = 200mA to 800mA
Load Transient Response
ILOAD = 200mA to 1.2A
CH1
CH2
CH2
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
ACT4082A-010
CH1
ACT4082A-009
ILOAD = 0mA
Start-up Waveforms
ILOAD = 1A
CH1
CH2
CH2
CH3
CH4
CH3
CH1: VEN, 2V/div
CH2: VOUT, 2V/div
CH3: VSW, 10V/div
CH4: IL, 1A/div
TIME: 400µs/div
CH1: VOUT, 2V/div
CH2: VSW, 10V/div
CH3: IL, 1A/div
TIME: 200µs/div
Steady State Switching Waveforms
ACT4082A-012
ACT4082A-011
ILOAD = 1A
CH1
Hiccup Mode Switching Waveforms
CH1
CH2
CH3
CH2
CH1: VOUT, 100mV/div, (AC COUPLED)
CH2: IL, 1A/div
TIME: 1ms/div
CH1: VOUT, 50mV/div, (AC COUPLED)
CH2: VSW, 10V/div
CH3: IL, 500mA/div
TIME: 400ns/div
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ACT4082A
Active-Semi
Rev0, 16-May-08
FUNCTIONAL BLOCK DIAGRAM
IN
CSA
EN
REGULATOR
& UVLO
BST
CONTROL
OSCILLATOR
SOFT-START
PWM Comparator
ILIM Comparator
HICCUP
Q1
DRIVER
SW
REFERENCE
& THERMAL
SHUTDOWN
COMPENSATION
EA
FB
G
in setting the ACT4082A's transient response and
ensuring stability. For most applications, choosing
RFB1 = 49.9kΩ provides good results. For applications with output voltages of 1.8V or lower, use a
larger RFB1 value such as 80.6kΩ. Once RFB1 is
chosen, use the following equation to choose RFB2:
FUNCTIONAL DESCRIPTION
The ACT4082A is a current-mode step-down
DC/DC converter that provides excellent transient
response with no extra external compensation components. This device contains an internal, lowresistance, high-voltage power MOSFET, and operates at a high 1.4MHz operating frequency to ensure a compact, high-efficiency design with excellent AC and DC performance.
RFB2 =
RFB1
(1)
⎛ VOUT
⎞
−1⎟
⎜
0
.
81
V
⎝
⎠
Setting the Output Voltage
Selecting the Inductor
An external voltage divider is used to set the output
voltage, as well as provide a known impedance
from VOUT to FB for compensation purposes. Connect a 50kΩ resistor from the output to FB to ensure
stable compensation, and select the bottom resistor
to provide the desired regulation voltage.
The ACT4082A was optimized for use with a 4.7µH
inductor. When choosing an inductor, choose one
with a DC resistance of less than 250mΩ and a DC
current rating that is typically 30% higher than the
maximum load current.
During typical operation, the inductor maintains a
continuous current to output load. The inductor
current has a ripple that is dependent on the
inductance value.
Figure 1:
Output Voltage Setting
Higher inductance reduces the peak-to-peak ripple
current. The trade off for high inductance value is
the increase in inductor core size and series
resistance, and a reduction in current handling
capability.
VOUT
ACT4082A
RFB1
FB
RFB2
If efficiency at light loads (such as less than 100mA)
is critical in the application, a larger inductor is
recommended.
The feedback resistor (RFB1) interacts with the internal compensation network, and plays an important
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ACT4082A
Active-Semi
Rev0, 16-May-08
Rectifier Diode
Shutdown Control
Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The
Schottky diode must have current rating higher than
the maximum output current and the reverse voltage rating higher than the maximum input voltage
(see Figure 2).
The ACT4082A enable pin provides several features for adjusting and sequencing the power supply. An internal 2µA current source pull-up, and a
precision 1.24V comparator with hysteresis. With
these components, a user has the flexibility of using
the EN pin as:
Selecting the Input Capacitor
1) A digital on/off control by pulling down the EN
current source with an external open-drain transistor. The voltage at EN is internally clamped to
6V.
For best performance choose a ceramic type capacitor with X5R or X7R dielectrics due to their low
ESR and small temperature coefficients. However,
low ESR tantalum or electrolytic types may also be
used, provided that the RMS ripple current rating is
higher than 50% of the output current. For most
applications, a 10µF capacitor is sufficient. The
input capacitor should be placed close to the IN and
G pins of the IC, with shortest possible traces. In
the case of tantalum or electrolytic types, connect a
small parallel 0.1µF ceramic capacitor right next to
the IC.
2) A sequenced power supply by tying the EN pin
through a resistor to the output of another power
supply. The IC will be enabled when the voltage
at EN exceeds 1.24V, or a resistor divider can be
used to adjust the turn-on threshold.
3) An always-on converter by floating the EN pin or
pulling EN to a desired voltage with a high value
(1MΩ) external resistor. EN is internally clamped
at 6V and will dissipate power if an external resistor attempts to pull EN above the 6V clamp
voltage.
Selecting the Output Capacitor
A 22µF ceramic capacitor with X5R or X7R dielectric provides the best results over a wide range of
applications.
4) Line UVLO. If desired, to achieve a UVLO voltage that is higher than the internal UVLO, an
external resistor divider from VIN to EN to GND
can be used to disable the ACT4082A until a
higher input voltage is achieved. For example, it
is not useful for a converter with 9V output to
start up with a 4.2V input voltage, as the output
cannot reach regulation. To enable the ACT4082A when the input voltage reaches 12V, a
9kΩ/1kΩ resistor divider from IN to GND can be
connected to the EN pin. Both the precision 1.2V
threshold and 80mV hysteresis are multiplied by
the resistor ratio, providing a proportional 6.67%
hysteresis for any startup threshold. For the example of a 12V enable threshold, the turn off
threshold would be 11.2V.
The output capacitor also needs to have low ESR
to keep low output voltage ripple. The output ripple
voltage is:
VRIPPLE = IOUTMAX K RIPPLE RESR +
VIN
2
8 × fSW LCOUT
(2)
where IOUTMAX is the maximum output current,
KRIPPLE is the ripple factor (typically 20% to 30%),
RESR resistance is the ESR of the output capacitor,
fSW is the switching frequency, L is the inductor
value, and COUT is the output capacitance.
In the case of ceramic output capacitors, RESR is
very small and does not contribute to the ripple. In
the case of tantalum or electrolytic type, the ripple is
dominated by RESR multiplied by the ripple current.
In that case, the output capacitor is chosen to have
sufficiently low due to ESR, typically choose a capacitor with less than 50mΩ ESR.
5) Power supply sequencing. By connecting a small
capacitor from EN to GND, the 2µA current
source and 1.24V threshold can provide a stable
and predictable delay between startup of multiple
power supplies. For example, a startup delay of
roughly 10mS is provided using 150nF, and
roughly 20mS by using 330nF. The EN current
source is active anytime an input supply is applied, so disabling the IC or resetting the delay
requires an external open-drain pull-down device
to reset the capacitor and hold the EN pin low for
shutdown.
External Bootstrap Diode
An external bootstrap diode (D2 in Figure 2) is recommended if the input voltage is less than 5.5V or if
there is a 5V system rail available. This diode helps
strengthen gate drive at lower input voltages, resulting in lower on-resistance and higher efficiency.
Low cost diodes, such as 1N4148 or BAT54, are
suitable for this application.
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ACT4082A
Active-Semi
Rev0, 16-May-08
Soft-Start
Frequency Foldback
The ACT4082A provides an internal soft-start feature, which ramps the output voltage and output
current are from 0 to the full value over 0.5 milliseconds. This feature prevents output voltage overshoot at light loads as well as to prevent large inrush currents upon startup. The soft-start circuitry is
internally reset anytime the IC is disabled using the
EN pin, as well as if the IC reaches hiccup mode or
thermal shutdown. In all of these cases, soft-start
provides a smooth, controlled restart after the fault
is removed.
The voltage at FB is monitored by a comparator to
detect an extreme output overload condition. If the
voltage at the FB pin falls to below 0.3V, the internal oscillator slows to a decreased frequency of
467kHz, 33% of the nominal value. This prevents
the inductor current from rising excessively during a
dead-short condition, potentially resulting in inductor saturation.
Figure 2:
ACT4082A Typical 5V/1.2A Output Application
Optional Connection:
IN if VIN < 5.5V
OUT if VOUT < 5.5V
VIN
2
IN
BST
6
C1
10µF
ACT4082A SW
ON
OFF
3
C3
22nF
D1
B230A
EN
FB
G
4
RFB2
5
Innovative PowerTM
1
D2
1N4148
(Optional)
-8-
9.53k?
Ω
1%
L1
4.7µH
C2
22µF
VOUT
5V
RFB1
49.9k?
Ω
1%
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ACT4082A
Active-Semi
Rev0, 16-May-08
Figure 3:
ACT4082A Optimized for Minimal External Components
The ACT4082A with provides excellent AC and DC results across a wide range of external component combinations. The circuit of
Figure 3 can be used to generate a 5V output from a 12V input utilizing a smaller (i.e. lower-cost) output capacitor while maintaining
good performance.
VIN
2
IN
BST
6
C1
10µF
ACT4082ASW
ON
OFF
3
C3
22nF
1
D1
B230A
EN
FB
G
4
RFB2
5
28.7k?
Ω
1%
L1
4.7µH
C2
4.7µF
RFB1
Ω
150k?
1%
Figure 4:
Figure 5:
Circuit of Figure 3 (ILOAD = 150mA to 850mA)
Circuit of Figure 3 (ILOAD = 1A)
ACT4082A-014
CH1
ACT4082A-013
Circuit of Figure 3
ILOAD = 150mA to 850mA
Circuit of Figure 3
ILOAD = 1A
CH1
CH2
VOUT
5V
CH2
CH1: ILOAD, 500mA/div
CH2: VOUT, 100mV/div (AC Coupled)
TIME: 200µs/div
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CH1: VSW, 10V/div
CH2: VOUT, 20mV/div (AC Coupled)
TIME: 400ns/div
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ACT4082A
Active-Semi
Rev0, 16-May-08
Hiccup Mode
If the ACT4082A transitions from normal operation
to a severe overload condition (the voltage at FB
falls below 0.3V), the controller automatically enters
"Hiccup Mode" to provide maximum protection to
the system. In hiccup mode, the IC stops switching,
clears the soft-start circuitry, then attempts to restart. If the overload condition has been removed,
the IC will start up normally and continue regulating.
In the case of a sustained overload, however, the
IC will attempt to regulate for a period of time equal
to 3x the soft-start period (1.5ms). If the overload
condition persists until the end of this period, the IC
will begin another hiccup cycle. This hiccup-mode
control scheme minimizes power dissipation during
severe overload conditions, and ensures that the
ACT4082A responds quickly to instantaneous severe overload conditions while providing immunity
to false hiccups that may occur with a heavily
loaded output.
Thermal Shutdown
The ACT4082A automatically turns off when the IC
junction temperature exceeds 160°C, and reenables when the IC junction temperature drops by
10°C (typ).
PC Board Layout
The high current paths at G, IN and SW should be
placed very close to the device with short, direct
and wide traces. The input capacitor needs to be as
close as possible to the IN and G pins. The external
feedback resistors should be placed next to the FB
pin. Keep the switch node traces short and away
from the feedback network and use shielded
inductors.
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ACT4082A
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Rev0, 16-May-08
PACKAGE OUTLINE
SOT23-6 PACKAGE OUTLINE AND DIMENSIONS
D
θ
b
SYMBOL
0.2
c
e
e1
DIMENSION IN
MILLIMETERS
DIMENSION IN
INCHES
MIN
MAX
MIN
MAX
A
1.050
1.250
0.041
0.049
A1
0.000
0.100
0.000
0.004
A2
1.050
1.150
0.041
0.045
b
0.300
0.500
0.012
0.020
c
0.100
0.200
0.004
0.008
D
2.820
3.020
0.111
0.119
E
1.500
1.700
0.059
0.067
E1
2.650
2.950
0.104
0.116
e
e1
L
0.950 TYP
1.800
2.000
0.700 REF
0.037 TYP
0.071
0.079
0.028 REF
L1
0.300
0.600
0.012
0.024
θ
0°
8°
0°
8°
Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. Users should evaluate each
product to make sure that it is suitable for their applications. Active-Semi products are not intended or authorized for use
as critical components in life-support devices or systems. Active-Semi, Inc. does not assume any liability arising out of
the use of any product or circuit described in this datasheet, nor does it convey any patent license.
Active-Semi and its logo are trademarks of Active-Semi, Inc. For more information on this and other products, contact
sales@active-semi.com or visit http://www.active-semi.com. For other inquiries, please send to:
1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044, USA
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