ACT4072_08 [ACTIVE-SEMI]
Wide Input 2A Step Down Converter; 宽电压输入2A降压转换器
| 型号： | ACT4072_08 |
| 厂家： | 
ACTIVE-SEMI, INC |
| 描述： | Wide Input 2A Step Down Converter |
| 文件： | 总10页 (文件大小：266K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Active- Semi
ACT4072
Rev2, 27-May-08
Wide Input 2A Step Down Converter
FEATURES
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.
• 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
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.
• 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-Powered Equipment
• Set-Top Boxes
• Telecom Power Supplies
• DSL and Cable Modems and Routers
TYPICAL APPLICATION CIRCUIT
BS
Up to 30V
VIN
IN
SW
VOUT
ACT4072
EN
FB
ENABLE
G
COMP
+
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ACT4072
Active- Semi
Rev2, 27-May-08
ORDERING INFORMATION
PART NUMBER
ACT4072SH
TEMPERATURE RANGE
PACKAGE
SOP-8
PINS
PACKING
TUBE
-40°C to 85°C
-40°C to 85°C
8
8
ACT4072SH-T
SOP-8
TAPE & REEL
PIN CONFIGURATION
BS
1
N/C
EN
8
7
6
5
IN
2
ACT4072SH
SW
G
COMP
FB
3
4
SOP-8
PIN DESCRIPTIONS
PIN
PIN NAME
NUMBER
PIN DESCRIPTION
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.
1
2
BS
IN
Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in Ap-
plication Information section.
3
4
SW
G
Switch Output. Connect this pin to the switching end of the inductor.
Ground.
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.
5
6
FB
COMP
Compensation Pin. See Compensation Techniques in Application Information section.
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.
7
8
EN
N/C
Not Connected.
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Copyright © 2008 Active-Semi, Inc.
ACT4072
Active- Semi
Rev2, 27-May-08
ABSOLUTE MAXIMUM RATINGSc
PARAMETER
VALUE
UNIT
V
IN to G
-0.3 to +34
-0.3 to VIN + 0.3
-1 to VIN + 1
-0.3 to +8
-0.3 to +6
Internally limited
105
EN to G
V
SW to G
V
BS to SW
V
FB, COMP to G
V
Continuous SW Current
Junction to Ambient Thermal Resistance (θJA)
Maximum Power Dissipation
Operating Junction Temperature
Storage Temperature
A
°C/W
W
0.76
-40 to 150
-55 to 150
300
°C
°C
°C
°C
Lead Temperature (Soldering, 10 sec)
Ambient Operating Temperature
-40 to 85
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
SYMBOL
VIN
TEST CONDITIONS
MIN
TYP MAX UNIT
Input Voltage
4.5
30
V
V
Feedback Voltage
VFB
VIN = 12V
1.198 1.222 1.246
High-Side Switch On Resistance
Low-Side Switch On Resistance
SW Leakage
RONH
RONL
0.13
10
Ω
Ω
V
EN = 0
0
3.3
2
10
µA
A
Current Limit
ILIM
GCOMP
GEA
2.4
340
0.7
COMP to Current Limit Transconductance
Error Amplifier Transconductance
Error Amplifier DC Gain
A/V
µA/V
V/V
kHz
kHz
%
∆ICOMP = ±10µA
550
4000
420
60
88
0
AVEA
fSW
Switching Frequency
500
1.3
Short Circuit Switching Frequency
Maximum Duty Cycle
VFB = 0
DMAX
DMIN
VFB = 1.1V, PWM mode
VFB = 1.4V, PFM mode
Hysteresis = 0.1V
Minimum Duty Cycle
%
Enable Threshold Voltage
Enable Pull Up Current
1
V
2
µA
µA
mA
°C
Supply Current in Shutdown
IC Supply Current in Operation
Thermal Shutdown Temperature
VEN = 0
6
20
2
VEN = 3V, not switching
0.8
160
Hysteresis = 10°C
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ACT4072
Active- Semi
Rev2, 27-May-08
FUNCTIONAL BLOCK DIAGRAM
IN
2µA
REGULATOR
ENABLE
&
EN
BS
REFERENCE
CURRENT SENSE
AMPLIFIER
+
-
COMP
ERROR
AMPLIFIER
1.222V
+
-
0.13ꢀ
HIGH-SIDE
POWER
+ -
-
+
PWM
COMP
FB
SWITCH
SW
FOLDBACK
CONTROL
OSCILLATOR
&
LOGIC
RAMP
10ꢀ LOW-SIDE
POWER SWITCH
THERMAL
SHUTDOWN
G
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.
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:
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.
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.
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.
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.
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ACT4072
Active- Semi
Rev2, 27-May-08
APPLICATIONS INFORMATION
Input Capacitor
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 ≈ 10kꢀ and determine
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.
R
FB1 from the output voltage:
VOUT
⎛
⎜
⎞
⎟
(1)
RFB1 = RFB2
-1
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.
1.222V
⎝
⎠
Figure 1:
Output Voltage Setting
VOUT
ACT4072
RFB1
FB
RFB2
Output Capacitor
The output capacitor also needs to have low ESR to
keep low output voltage ripple. The output ripple
voltage is:
Inductor Selection
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:
RRIPPLE = LOUTMAXKRIPPLERESR
VIN
+
(3)
28fSW 2LCOUT
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.
VOUT
×
(
V -VOUT
)
IN
(2)
L =
VINfSWIOUTMAXKRIPPLE
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.
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.
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 50mꢀ ESR.
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.
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.
Table 1:
Typical Inductor Values
VOUT
1.5V
1.8V
2.5V
3.3V
5V
L
6.8µH
6.8µH
10µH
15µH
22µH
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ACT4072
Active- Semi
Rev2, 27-May-08
Stability compensation
Figure 2:
STEP 2. Set the zero fZ1 at 1/4 of the cross over
frequency. If RCOMP is less than 15kꢀ, the equation
for CCOMP is:
Stability Compensation
1.8 ×10 −5
RCOMP
CCOMP
=
(F)
(10)
COMP
ACT4072
If RCOMP is limited to 15kꢀ, then the actual cross
CCOMP
over frequency is 3.4/(VOUTCOUT). Therefore:
c
CCOPM2
RCOMP
CCOMP =1.3x10−5VOUTCOUT
(11)
(F)
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
c: CCOMP2 is needed only for high ESR output capacitors or PCB
parasitics
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:
C
COMP2 is:
−6
⎛
⎞
1.1x10
COUT
⎜
⎜
⎟
⎟
RESROUT ≥ Min
,0.012VOUT
(ꢀ)
(12)
⎝
⎠
1.222V
AVDC
=
AVEAGCOMP
(4)
IOUT
And the proper value for CCOMP2 is:
The dominant pole P1 is due to CCOMP
:
COUTRESROUT
CCOMP2
=
(13)
GEA
RCOMP
fP1
=
(5)
2πAVEACCOMP
A small value CCOMP2 such as 100pF may improve
stability against PCB layout parasitic effects.
The second pole P2 is the output pole:
Table 2 shows some calculated results based on the
compensation method above.
IOUT
fP2
=
(6)
(7)
2πVOUTCOUT
Table 2:
The first zero Z1 is due to RCOMP and CCOMP
:
Typical Compensation for Different Output volt-
ages and Output Capacitors
1
fZ1
=
2πRCOMPCCOMP
c
VOUT
2.5V
3.3V
5V
COUT
RCOMP CCOMP CCOMP2
And finally, the third pole is due to RCOMP and
COMP2 (if CCOMP2 is used):
22µF Ceramic
22µF Ceramic
22µF Ceramic
47µF SP CAP
47µF SP CAP
47µF SP CAP
8.2kꢀ 2.2nF
100pF
100pF
100pF
100pF
100pF
100pF
1nF
C
12kꢀ
15kꢀ
15kꢀ
15kꢀ
15kꢀ
1.5nF
1.5nF
1.5nF
1.8nF
2.7nF
15nF
22nF
27nF
1
fP3
=
(8)
2πRCOMPCCOMP2
2.5V
3.3V
5V
Follow the following steps to compensate the IC:
STEP 1. Set the cross over frequency at 1/10 of the
switching frequency via RCOMP
:
2.5V
3.3V
5V
470µF/6.3V/30mꢀ 15kꢀ
470µF/6.3V/30mꢀ 15kꢀ
470µF/6.3V/30mꢀ 15kꢀ
1nF
2πVOUTCOUT fSW
10GEAGCOMP1.222V
= 2.3x108VOUTCOUT
RCOMP
=
1nF
c: CCOMP2 is needed for board parasitic and high ESR output
capacitor.
(9)
(ꢀ)
Figure 3 shows an example ACT4072 application
circuit generating a 5V/2A output.
but limit RCOMP to 15kꢀ maximum.
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ACT4072
Active- Semi
Rev2, 27-May-08
Figure 3:
ACT4072 5V/2A Output Applicationc
C3
10nF
BS
L1 22µH/3A
R1 39.2k
Up to 30V
5V/2A
VIN
IN
SW
VOUT
IC1
EN ACT4072 FB
ENABLE
G
COMP
C4
C2
1.5nF
22µF/10V
ceramic or
47µH/6.3 SP
Cap
+
D1
C5
100pF
R2
12.1k
C1
10µF/35V
R3
15k
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.
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ACT4072
Active- Semi
Rev2, 27-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 3, unless otherwise specified.)
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
80
90
80
70
60
50
70
60
50
VIN = 6V
VIN = 30V
VIN = 12V
VIN = 25V
VIN = 12V
VIN = 8V
40
40
30
20
30
20
VOUT = 5V
L = 22µH
VOUT = 3.3V
L = 15µH
10
0
C
IN = 10µF
C
IN = 10µF
10
0
COUT = 22µF
COUT = 22µF
0.01
0.1
1
10
0.0
0.1
1
10
Output Current (A)
Output Current (A)
Switching Frequency vs. Input Voltage
Shutdown Supply Current vs. Input Voltage
18
16
14
430
425
420
415
410
405
12
10
8
6
4
2
0
5
10
2.0
0.5
1.0
2.5
15
20
25
30
0.0
1.5
Input Voltage (V)
Temperature (°C)
Surface Temperature vs. Output Current
Feedback Voltage vs. Temperature
80
70
1.27
1.25
VIN = 12V
VIN = 30V
60
50
1.23
1.21
1.19
40
30
20
VOUT=5V
L=22µH
CIN=10µF
COUT=22µF
VIN = 12V
1.17
0.0
1.5
2.0
-20
1.0
0.5
-40
20
60
0
40
80
120
100
Output Current (A)
Temperature (°C)
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ACT4072
Active- Semi
Rev2, 27-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 3, unless otherwise specified.)
Load Transient Response
Load Transient Response
VOUT
VOUT
200mV/div
200mV/div
2A
IOUT
1A
1A
IOUT
0A
VIN = 12V
VIN = 12V
100µs/div
100µs/div
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ACT4072
Active- Semi
Rev2, 27-May-08
PACKAGE OUTLINE
SOP-8 PACKAGE OUTLINE AND DIMENSIONS
D
C
DIMENSION IN DIMENSION
MILLIMETERS
IN INCHES
SYMBOL
MIN
1.350
0.100
1.350
0.330
0.190
4.700
3.800
5.800
MAX
1.750
0.250
1.550
0.510
0.250
5.100
4.000
6.300
MIN
0.053
0.004
0.053
0.013
0.007
0.185
0.150
0.228
MAX
A
A1
A2
B
0.069
0.010
0.061
0.020
0.010
0.201
0.157
0.248
θ
C
e
D
B
E
E1
e
1.270 TYP
0.050 TYP
L
0.400
0°
1.270
8°
0.016
0°
0.050
8°
θ
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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