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Copyright © 2008 Active-Semi, Inc.
TYPICAL APPLICATION CIRCUIT
ACT4072
Rev2, 27-May-08
Wide Input 2A Step Down Converter
ACT4072
BS
IN
EN
COMP
FB
SW
G
VIN
ENABLE
Up to 30V
+
VOUT
FEATURES
• 2A Output Current
• Up to 95% Efficiency
• Up to 30V Input Range
• 6µA Shutdown Supply Current
• 420kHz Switching Frequency
• Adjustable Output Voltage
• Cycle-by-Cycle Current Limit Protection
• Thermal Shutdown Protection
• Frequency Fold-Back at Short Circuit
• Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
• SOP-8 Package
APPLICATIONS
• TFT LCD Monitors or Televisions and HDTV
• Portable DVD Players
• Car-Powered or Battery -Po wered Equipment
• Set-Top Boxes
• Telecom Power Supplies
• DSL and Cable Modems and Routers
GENERAL DESCRIPTION
The ACT4072 is a current-mode step-down DC/DC
converter that generates up to 2A output current at
420kHz switching frequency. The device utilizes
Active-Semi’s proprietary ISOBCD30 process for
operation with input voltage up to 30V.
Consuming only 6µA in shutdown mode, the
ACT4072 is highly efficient with peak efficiency at
95% when in operation. Protection features include
cycle-by-cycle current limit, thermal shutdown, and
frequency fold-back at short circuit.
The ACT4072 is available in SOP-8 package and
requires very few external devices for operation.
A
cti ve-Sem i
ACT4072
Rev2, 27-May-08
Active-Semi
Innovative PowerTM - 2 - www.active-semi.com
Copyright © 2008 Active-Semi, Inc.
ORDERING INFORMATION
PART NUMBER TEMPERATURE RANGE PACKAGE PINS PACKING
ACT4072SH -40°C to 85°C SOP-8 8 TUBE
ACT4072SH-T -40°C to 85°C SOP-8 8 TAPE & REEL
PIN CONFIGURATION
PIN DESCRIPTIONS
SOP-8
PIN
NUMBER PIN NAME PIN DESCRIPTION
1 BS
Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Con-
nect a 10nF between this pin and SW.
2 IN
Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in Ap-
plication Information section.
3 SW Switch Output. Connect this pin to the switching end of the inductor.
4 G Ground.
5 FB
Feedback Input. The voltage at this pin is regulated to 1.222V. Connect to the resistor
divider between the output and ground to set output voltage.
6 COMP Compensation Pin. See Compensation Techniq ues in Application Information section.
7 EN
Enable Input. Drive higher than 1.3V or leave unconnected to enable the IC. Drive lower
than 0.7V to disable the IC. When disabled, the IC is in 6µA low current shutdown mode
and the output is discharged through the Low-Side Power Switch. This pin has a small
internal pull up current to a high level voltage when pin is not connected.
8 N/C Not Connected.
8
7
6
5
1
2
3
4
BS
IN
SW
GFB
COMP
EN
N/C
ACT4072SH
ACT4072
Rev2, 27-May-08
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Copyright © 2008 Active-Semi, Inc.
ABSOLUTE MAXIMUM RATINGSc
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TA= 25°C, unless otherwise specified.)
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.
PARAMETER VALUE UNIT
IN to G -0.3 to +34 V
EN to G -0.3 to VIN + 0.3 V
SW to G -1 to VIN + 1 V
BS to SW -0.3 to +8 V
FB, COMP to G -0.3 to +6 V
Continuous SW Current Internally limited A
Junction to Ambient Thermal Resistance (JA) 105 °C/W
Maximum Power Dissipation 0.76 W
Operating Junction Temperature -40 to 150 °C
Storage Temperature -55 to 150 °C
Lead Temperature (Soldering, 10 sec) 300 °C
Ambient Operating Temperature -40 to 85 °C
PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT
Input Voltage VIN 4.5 30 V
Feedback Voltage VFB V
IN = 12V 1.198 1.222 1.246 V
High-Side Switch On Resistance RONH 0.13
Low-Side Switch On Resistance RONL 10
SW Leakage VEN = 0 0 10 µA
Current Limit ILIM 2.4 3.3 A
COMP to Current Limit Transconductance GCOMP 2 A/V
Error Amplifier Transconductance GEA ICOMP = ±10µA 550 µA/V
Error Amplifier DC Gain AVEA 4000 V/V
Switching Frequency fSW 340 420 500 kHz
Short Circuit Switching Frequency VFB = 0 60 kHz
Maximum Duty Cycle DMAX V
FB = 1.1V, PWM mode 88 %
Minimum Duty Cycle DMIN V
FB = 1.4V, PFM mode 0 %
Enable Threshold Voltage Hysteresis = 0.1V 0.7 1 1.3 V
Enable Pull Up Current 2 µA
Supply Current in Shutdown VEN = 0 6 20 µA
IC Supply Current in Operation VEN = 3V, not switching 0.8 2 mA
Thermal Shutdown Temperature Hysteresis = 10°C 160 °C
ACT4072
Rev2, 27-May-08
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Copyright © 2008 Active-Semi, Inc.
FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL DESCRIPTION
As seen in the Functional Block Diagram, the
ACT4072 is a current mode pulse width modulation
(PWM) converter. The converter operates as fol-
lows:
A switching cycle starts when the rising edge of the
Oscillator clock output causes the High-Side Power
Switch to turn on and the Low-Side Power Switch to
turn off. With the SW side of the inductor now con-
nected to IN, the inductor current ramps up to store
energy in its magnetic field. The inductor current
level is measured by the Current Sense Amplifier
and added to the Oscillator ramp signal. If the result-
ing summation is higher than the COMP voltage, the
output of the PWM Comparator goes high. When
this happens or when Oscillator clock output goes
low, the High-Side Power Switch turns off and the
Low-Side Power Switch turns on. At this point, the
SW side of the inductor swings to a diode voltage
below ground, causing the inductor current to de-
crease and magnetic energy to be transferred to the
output. This state continues until the cycle starts
again.
The High-Side Power Switch is driven by logic using
the BS bootstrap pin as the positive rail. This pin is
charged to VSW + 6V when the Low-Side Power
Switch turns on.
The COMP voltage is the integration of the error
between the FB input and the internal 1.222V refer-
ence. If FB is lower than the reference voltage,
COMP tends to go higher to increase current to the
output. Current limit happens when COMP reaches
its maximum clamp value of 2.55V.
The Oscillator normally switches at 420kHz. How-
ever, if the FB voltage is less than 0.7V, then the
switching frequency decreases until it reaches a
minimum of 60kHz at VFB = 0.5V.
Shutdown Control
The ACT4072 has an enable input EN for turning
the IC on or off. When EN is less than 0.7V, the IC
is in 6µA low current shutdown mode and the out-
put is discharged through the Low-Side Power
Switch. When EN is higher than 1.3V, the IC is in
normal operation mode. EN is internally pulled up
with a 2µA current source and can be left uncon-
nected for always-on operation.
Thermal Shutdown
The ACT4072 automatically turns off when its junc-
tion temperature exceeds 160°C.
IN
EN
COMP
FB
BS
SW
LOGIC
THERMAL
SHUTDOWN
REGULATOR
&
REFERENCE
+
-
OSCILLATOR
&
RAMP
FOLDBACK
CONTROL
1.222V
ERROR
AMPLIFIER
2µA
ENABLE
0.13O
HIGH-SIDE
POWER
SWITCH
G
+- +-
-
+
PWM
COMP
CURRENT SENSE
AMPLIFIER
10O LOW-SIDE
POWER SWITCH
ACT4072
Rev2, 27-May-08
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Copyright © 2008 Active-Semi, Inc.
Output Voltage Setting
Figure 1 shows the connections for setting the out-
put voltage. Select the proper ratio of the two feed-
back resistors RFB1 and RFB2 based on the output
voltage. Typically, use RFB2 10k and determine
RFB1 from the output voltage:
The inductor maintains a continuous current to the
output load. This inductor current has a ripple that is
dependent on the inductance value: higher induc-
tance 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 the
reduction in current handling capability. In general,
select an inductance value L based on ripple current
requirement:
VOUT 1.5V 1.8V 2.5V 3.3V 5V
L 6.8µH 6.8µH 10µH 15µH 22µH
⎟
⎠
⎞
⎜
⎝
⎛
=1
V222.1V
RR OUT
FB21FB -
()
RIPPLEOUTMAXSWIN
OUTINOUT KIfV VVV
L-×
=
The input capacitor needs to be carefully selected to
maintain sufficiently low ripple at the supply input of
the converter. A low ESR capacitor is highly recom-
mended. Since a large current flows in and out of
this capacitor during switching, its ESR also affects
efficiency.
The input capacitance needs to be higher than
10µF. The best choice is the ceramic type, how-
ever, 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. 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, they can be
further away if a small parallel 0.1µF ceramic ca-
pacitor is placed right next to the IC.
The output capacitor also needs to have low ESR to
keep low output voltage ripple. The output ripple
voltage is:
where IOUTMAX is the maximum output current,
KRIPPLE is the ripple factor, RESR is the ESR
resistance of the output capacitor, fSW is the
switching frequency, L is the inductor value, COUT is
the output capacitance.
In the case of ceramic output capacitors, RESR is
very small and does not contribute to the ripple.
Therefore, a lower capacitance value can be used
for ceramic type, typically choose a capacitance of
about 22µF.
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 ca-
pacitor with less than 50m ESR.
Rectifier Diode
Use a Schottky diode as the rectifier to conduct cur-
rent when the High-Side Power Switch is off. The
Schottky diode must have current rating higher than
the maximum output current and the reverse volt-
age rating higher than the maximum input voltage.
Output Capacitor
Input Capacitor
APPLICATIONS INFORMATION
where VIN is the input voltage, VOUT is the output
voltage, fSW is the switching frequency, IOUTMAX is the
maximum output current, and KRIPPLE is the ripple
factor. Typically, choose KRIPPLE = 20% to 30%
corresponding to the peak-to-peak ripple current
being 20% to 30% of the maximum output current.
With this inductor value (Table 1), the peak inductor
current is IOUT × (1 + KRIPPLE / 2). Make sure that this
peak inductor current is less that the 2.4A current
limit. Finally, select the inductor core size so that it
does not saturate at 2.4A.
(1)
(2)
(3)
Figure 1:
Output Voltage Setting
ESRRIPPLEOUTMAXRIPPLE RKLR
=
OUT
2
SW
IN
LCf28 V
+
Table 1:
Typical Inductor Values
Inductor Selection
FB
ACT4072 RFB1
RFB2
VOUT
ACT4072
Rev2, 27-May-08
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Copyright © 2008 Active-Semi, Inc.
Stability compensation
The feedback system of the IC is stabilized by the
components at the COMP pin, as shown in Figure
2. The DC loop gain of the system is determined by
the following equation:
COMPVEA
OUT
VDC GA
IV222.1
A=
The dominant pole P1 is due to CCOMP:
COMPVEA
EA
1P CA2 G
f
π
=
COMPCOMP
1Z CR2 1
f
π
=
And finally, the third pole is due to RCOMP and
CCOMP2 (if CCOMP2 is used):
COMP2COMP
3P CR2 1
f
π
=
Follow the following steps to compensate the IC:
STEP 1. Set the cross over frequency at 1/10 of the
switching frequency via RCOMP:
but limit RCOMP to 15k maximum.
OUTOUT
OUT
2P CV2 I
f
π
=
The first zero Z1 is due to RCOMP and CCOMP:
The second pole P2 is the output pole:
STEP 2. Set the zero fZ1 at 1/4 of the cross over
frequency. If RCOMP is less than 15k, the equation
for CCOMP is:
If RCOMP is limited to 15k, then the actual cross
over frequency is 3.4/(VOUTCOUT). Therefore:
OUTOUT
5
COMP CV10x3.1C −
=
STEP 3. If the output capacitor’s ESR is high
enough to cause a zero at lower than 4 times the
cross over frequency, an additional compensation
capacitor CCOMP2 is required. The condition for using
CCOMP2 is:
V012.0,
C10x1.1
MinR OUT
OUT
6
ESROUT ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
≥
−
And the proper value for CCOMP2 is:
COMP
ESROUTOUT
2COMP RRC
C=
A small value CCOMP2 such as 100pF may improve
stability against PCB layout parasitic effects.
Table 2 shows some calculated results based on the
compensation method above.
Table 2:
Typical Compensation for Different Outpu t volt-
ages and Output Cap acitors
VOUT C
OUT R
COMP C
COMP C
COMP2c
2.5V 22µF Ceramic 8.2k 2.2nF 100pF
3.3V 22µF Ceramic 12k 1.5nF 100pF
5V 22µF Ceramic 15k 1.5nF 100pF
2.5V 47µF SP CAP 15k 1.5nF 100pF
3.3V 47µF SP CAP 15k 1.8nF 100pF
5V 47µF SP CAP 15k 2.7nF 100pF
2.5V 470µF/6.3V/30m 15k 15nF 1nF
3.3V 470µF/6.3V/30m 15k 22nF 1nF
5V 470µF/6.3V/30m 15k 27nF 1nF
OUTOUT
8COMPEA
SWOUTOUT
COMP
CV10x3.2 V222.1GG10 fCV2
R
=
=
π
(10)
(12)
(11)
(13)
(4)
(5)
(6)
(7)
(8)
() (9)
()
(F)
(F)
c: CCOMP2 is needed for board parasitic and high ESR output
capacitor.
c: CCOMP2 is needed only for high ESR output capacitors or PCB
parasitics
Figure 2:
Stability Compensation
Figure 3 shows an example ACT4072 application
circuit generating a 5V/2A output.
COMP
5
COMP R108.1
C−
×
=
COMP
ACT4072
CCOPM2
CCOMP
RCOMP
c
ACT4072
Rev2, 27-May-08
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Copyright © 2008 Active-Semi, Inc.
Figure 3:
ACT4072 5V/2A Output Applicationc
c: D1 is a 40V, 3A Schottky diode with low forward voltage, an IR 30BQ040 or SK34 equivalent. C4 can be either a ceramic capacitor
(Panasonic ECJ-3YB1C226M) or SP-CAP (Specialty Polymer) Aluminum Electrolytic Capacitor such as Panasonic EEFCD0J470XR.
The SP-Cap is based on aluminum electrolytic capacitor technology, but uses a solid polymer electrolyte and has very stable capaci-
tance characteristics in both operating temperature and frequency compared to ceramic, polymer, and low ESR tantalum capacitors.
IC1
ACT4072
BS
IN
EN
COMP
FB
SW
G
VIN
ENABLE
Up to 30V
+
C1
10µF/35V
C2
1.5nF
R3
15k
C5
100pF
R2
12.1k
D1
L1 22µH/3A
C3
10nF
R1 39.2k
VOUT
C4
22µF/10V
ceramic or
47µH/6.3 SP
Cap
5V/2A
ACT4072
Rev2, 27-May-08
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Copyright © 2008 Active-Semi, Inc.
Surface Temperature vs. Output Current
TYPICAL PERFORMANCE CHARACTERISTICS
ACT4072-005
Output Current (A)
Surface Temperature (°C)
70
80
60
40
0.0 0.5 1.0 1.5 2.0
50
30
20
VIN = 30V
VIN = 12V
VOUT=5V
L=22µH
CIN=10µF
COUT=22µF
40
70
80
90
100
50
60
Efficiency (%)
Output Current (A)
ACT4072-001
30
20
10
0
0.01 0.1 1 10
Efficiency vs. Output Current
VOUT = 3.3V
L = 15µH
CIN = 10µF
COUT = 22µF
40
70
80
90
100
50
60
Efficiency (%)
0.0 0.1 1 10
Output Current (A)
ACT4072-002
Efficiency vs. Output Current
30
20
10
0
VOUT = 5V
L = 22µH
CIN = 10µF
COUT = 22µF
0.0
Temperature (°C)
0.5 1.0 1.5 2.0 2.5
ACT4072-003
415
420
430
410
405
Switching Frequency(kHz)
Switching Frequency vs. Input Voltage
425
ACT4072-004
Shutdown Supply Current (mA)
Shutdown Supply Current vs. Input Voltage
2
4
6
16
18
12
10
8
14
0
5 20 25 30
10
Input Voltage (V)
15
ACT4072-006
Temperature (°C)
Feedback Voltage (V)
1.17
1.19
1.21
1.23
1.25
1.27
Feedback Voltage vs. Temperature
0 40 80 120
-20 20 60
100
-40
VIN = 12V
VIN = 6V
VIN = 12V
VIN = 25V
VIN = 8V
VIN = 12V
VIN = 30V
(Circuit of Figure 3, unless otherwise specified.)
ACT4072
Rev2, 27-May-08
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Copyright © 2008 Active-Semi, Inc.
TYPICAL PERFORMANCE CHARACTERISTICS
VOUT
200mV/div
2A
IOUT
1A
ACT4072-007
Load Transient Response
100µs/div
ACT4072-008
Load Transient Response
100µs/div
VOUT
200mV/div
VIN = 12V VIN = 12V
(Circuit of Figure 3, unless otherwise specified.)
1A
IOUT
0A
ACT4072
Rev2, 27-May-08
Active-Semi
Innovative PowerTM - 10 - www.active-semi.com
Copyright © 2008 Active-Semi, Inc.
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 a pplications . Active-Semi products ar e not intende d or authori zed 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, Ca lifornia 94085-4044, USA
PACKAGE OUTLINE
SOP-8 PACKAGE OUTLINE AND DIMENSIONS
SYMBOL DIMENSION IN
MILLIMETERS DIMENSION
IN INCHES
MIN MAX MIN MAX
A 1.350 1.750 0.053 0.069
A1 0.100 0.250 0.004 0.010
A2 1.350 1.550 0.053 0.061
B 0.330 0.510 0.013 0.020
C 0.190 0.250 0.007 0.010
D 4.700 5.100 0.185 0.201
E 3.800 4.000 0.150 0.157
E1 5.800 6.300 0.228 0.248
e 1.270 TYP 0.050 TYP
L 0.400 1.270 0.016 0.050
0° 8° 0° 8°
A
A2
A1
L
?
C
E
D
E1
B
e
