ACTIVE-SEMI ACT4072SH Wide input 2a step down converter Datasheet

ACT4072
Active-Semi
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
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.
420kHz Switching Frequency
Adjustable Output Voltage
Cycle-by-Cycle Current Limit Protection
Thermal Shutdown Protection
The ACT4072 is available in SOP-8 package and
requires very few external devices for operation.
Frequency Fold-Back at Short Circuit
Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
• SOP-8 Package
APPLICATIONS
•
•
•
•
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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
VIN
BS
Up to 30V
IN
SW
VOUT
ACT4072
EN
ENABLE
FB
G
COMP
+
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-1-
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Copyright © 2008 Active-Semi, Inc.
ACT4072
Active-Semi
Rev2, 27-May-08
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
BS
1
IN
2
8
N/C
7
EN
ACT4072SH
SW
3
6
COMP
G
4
5
FB
SOP-8
PIN DESCRIPTIONS
PIN
NUMBER
PIN NAME
1
BS
Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect 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 Application Information section.
3
SW
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 Techniques in Application Information section.
PIN DESCRIPTION
Switch Output. Connect this pin to the switching end of the inductor.
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.
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-2-
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Copyright © 2008 Active-Semi, Inc.
ACT4072
Active-Semi
Rev2, 27-May-08
ABSOLUTE MAXIMUM RATINGSc
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
Internally limited
A
Junction to Ambient Thermal Resistance (θJA)
105
°C/W
Maximum Power Dissipation
0.76
W
Operating Junction Temperature
-40 to 150
°C
Storage Temperature
-55 to 150
°C
300
°C
-40 to 85
°C
Continuous SW Current
Lead Temperature (Soldering, 10 sec)
Ambient Operating Temperature
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
Input Voltage
VIN
Feedback Voltage
VFB
TEST CONDITIONS
MIN
TYP
4.5
VIN = 12V
1.198
1.222
MAX UNIT
30
V
1.246
V
High-Side Switch On Resistance
RONH
0.13
Ω
Low-Side Switch On Resistance
RONL
10
Ω
SW Leakage
Current Limit
COMP to Current Limit Transconductance
VEN = 0
ILIM
2.4
GCOMP
Error Amplifier Transconductance
GEA
Error Amplifier DC Gain
AVEA
Switching Frequency
0
∆ICOMP = ±10µA
fSW
Short Circuit Switching Frequency
340
10
µA
3.3
A
2
A/V
550
µA/V
4000
V/V
420
500
kHz
VFB = 0
60
kHz
Maximum Duty Cycle
DMAX
VFB = 1.1V, PWM mode
88
%
Minimum Duty Cycle
DMIN
VFB = 1.4V, PFM mode
0
%
Enable Threshold Voltage
Hysteresis = 0.1V
Enable Pull Up Current
1
1.3
2
Supply Current in Shutdown
VEN = 0
IC Supply Current in Operation
Thermal Shutdown Temperature
Innovative PowerTM
0.7
V
µA
6
20
µA
VEN = 3V, not switching
0.8
2
mA
Hysteresis = 10°C
160
-3-
°C
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Copyright © 2008 Active-Semi, Inc.
ACT4072
Active-Semi
Rev2, 27-May-08
FUNCTIONAL BLOCK DIAGRAM
IN
EN
COMP
1.222V
FB
2µA
ENABLE
REGULATOR
&
REFERENCE
BS
CURRENT SENSE
AMPLIFIER
+
-
ERROR
AMPLIFIER
+
FOLDBACK
CONTROL
+ - + PWM
0.13O
Ω
HIGH-SIDE
POWER
SWITCH
COMP
SW
OSCILLATOR
&
RAMP
LOGIC
10O
Ω LOW-SIDE
POWER SWITCH
THERMAL
SHUTDOWN
G
FUNCTIONAL DESCRIPTION
As seen in the Functional Block Diagram, the
ACT4072 is a current mode pulse width modulation
(PWM) converter. The converter operates as follows:
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 connected 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 resulting 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 decrease 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.
Innovative PowerTM
-4-
The COMP voltage is the integration of the error
between the FB input and the internal 1.222V reference. 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. However, 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 output 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 unconnected for always-on operation.
Thermal Shutdown
The ACT4072 automatically turns off when its junction temperature exceeds 160°C.
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Copyright © 2008 Active-Semi, Inc.
ACT4072
Active-Semi
Rev2, 27-May-08
APPLICATIONS INFORMATION
Output Voltage Setting
Input Capacitor
Figure 1 shows the connections for setting the output voltage. Select the proper ratio of the two feedback resistors RFB1 and RFB2 based on the output
voltage. Typically, use RFB2 ≈ 10kΩ and determine
RFB1 from the output voltage:
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 recommended. Since a large current flows in and out of
this capacitor during switching, its ESR also affects
efficiency.
⎛ V
⎞
R FB1 = R FB2 ⎜ OUT - 1 ⎟
⎝ 1 .222 V
⎠
Figure 1:
(1)
The input capacitance needs to be higher than
10µF. The best choice is the ceramic type, 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. 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 capacitor is placed right next to the IC.
Output Voltage Setting
V OUT
ACT4072
R FB1
FB
R FB2
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 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 the
reduction in current handling capability. In general,
select an inductance value L based on ripple current
requirement:
L=
VOUT × (VIN - VOUT )
VIN fSW IOUTMAXK RIPPLE
RRIPPLE = LOUTMAXK RIPPLERESR
+
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 capacitor with less than 50mΩ 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 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.
Table 1:
Typical Inductor Values
1.5V
1.8V
2.5V
3.3V
5V
L
6.8µH
6.8µH
10µH
15µH
22µH
Innovative PowerTM
(3)
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.
(2)
VOUT
VIN
2
28 fSW LCOUT
-5-
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Copyright © 2008 Active-Semi, Inc.
ACT4072
Active-Semi
Rev2, 27-May-08
Stability compensation
STEP 2. Set the zero fZ1 at 1/4 of the cross over
frequency. If RCOMP is less than 15kΩ, the equation
for CCOMP is:
Figure 2:
Stability Compensation
C COMP =
COMP
ACT4072
CCOPM2c
CCOMP = 1.3 x10 −5VOUTCOUT
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:
1.222V
AVEAGCOMP
IOUT
CCOMP2 =
(5)
IOUT
2πVOUTCOUT
And finally, the third pole is due to RCOMP and
CCOMP2 (if CCOMP2 is used):
fP 3 =
1
(8)
2πRCOMP CCOMP2
Follow the following steps to compensate the IC:
STEP 1. Set the cross over frequency at 1/10 of the
switching frequency via RCOMP:
RCOMP =
2πVOUT COUT fSW
10GEAGCOMP 1.222V
= 2.3 x10 VOUT COUT
8
(Ω)
RCOMP CCOMP CCOMP2c
VOUT
COUT
2.5V
22µF Ceramic
8.2kΩ
2.2nF
100pF
3.3V
22µF Ceramic
12kΩ
1.5nF
100pF
5V
22µF Ceramic
15kΩ
1.5nF
100pF
2.5V
47µF SP CAP
15kΩ
1.5nF
100pF
3.3V
47µF SP CAP
15kΩ
1.8nF
100pF
5V
47µF SP CAP
15kΩ
2.7nF
100pF
2.5V
470µF/6.3V/30mΩ
15kΩ
15nF
1nF
3.3V
470µF/6.3V/30mΩ
15kΩ
22nF
1nF
5V
470µF/6.3V/30mΩ
15kΩ
27nF
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 15kΩ maximum.
Innovative PowerTM
(13)
Typical Compensation for Different Output voltages and Output Capacitors
(7)
2πRCOMP CCOMP
COUT RESROUT
RCOMP
Table 2:
The first zero Z1 is due to RCOMP and CCOMP:
fZ 1 =
(12)
Table 2 shows some calculated results based on the
compensation method above.
(6)
1
⎞
⎟⎟ (Ω)
⎠
A small value CCOMP2 such as 100pF may improve
stability against PCB layout parasitic effects.
The second pole P2 is the output pole:
fP 2 =
(11)
And the proper value for CCOMP2 is:
The dominant pole P1 is due to CCOMP:
fP 1
(F)
⎛ 1.1x10 −6
R ESROUT ≥ Min ⎜⎜
,0.012VOUT
⎝ COUT
(4)
GEA
=
2 πAVEA CCOMP
(10)
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:
c: CCOMP2 is needed only for high ESR output capacitors or PCB
parasitics
AVDC =
(F)
If RCOMP is limited to 15kΩ, then the actual cross
over frequency is 3.4/(VOUTCOUT). Therefore:
CCOMP
RCOMP
1 . 8 × 10 − 5
R COMP
-6-
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ACT4072
Active-Semi
Rev2, 27-May-08
Figure 3:
ACT4072 5V/2A Output Applicationc
VIN
ENABLE
C3
10nF
BS
Up to 30V
IN
IC1
ACT4072
EN
G
+
C1
10µF/35V
SW
L1 22µH/3A
5V/2A
VOUT
R1 39.2k
FB
COMP
C2
1.5nF
C5
R2
100pF 12.1k
R3
15k
D1
C4
22µF/10V
ceramic or
47µH/6.3 SP
Cap
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 capacitance 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
VIN = 6V
90
80
Efficiency (%)
Efficiency (%)
80
60
VIN = 25V
50
VIN = 12V
40
30
20
0
70
VIN = 30V
60
VIN = 12V
50
VIN = 8V
40
30
20
VOUT = 3.3V
L = 15µH
CIN = 10µF
COUT = 22µF
10
ACT4072-002
90
70
100
ACT4072-001
100
VOUT = 5V
L = 22µH
CIN = 10µF
COUT = 22µF
10
0
0.01
0.1
1
10
0.0
0.1
Output Current (A)
Switching Frequency vs. Input Voltage
Shutdown Supply Current (mA)
Switching Frequency(kHz)
420
415
410
405
1.0
1.5
2.0
18
ACT4072-004
ACT4072-003
425
0.5
16
14
12
10
8
6
4
2
0
5
2.5
10
15
Surface Temperature vs. Output Current
30
1.27
VIN = 12V
Feedback Voltage (V)
VIN = 30V
60
ACT4072-006
Surface Temperature (°C)
25
Feedback Voltage vs. Temperature
ACT4072-005
80
50
40
VOUT=5V
VIN = 12V L=22µH
CIN=10µF
COUT=22µF
30
20
Input Voltage (V)
Temperature (°C)
70
10
Shutdown Supply Current vs. Input Voltage
430
0.0
1
Output Current (A)
1.25
1.23
1.21
1.19
1.17
20
0.0
0.5
1.0
1.5
2.0
-40
Output Current (A)
Innovative PowerTM
-20
0
20
40
60
80
100
120
Temperature (°C)
-8-
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Copyright © 2008 Active-Semi, Inc.
ACT4072
Active-Semi
Rev2, 27-May-08
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 3, unless otherwise specified.)
Load Transient Response
Load Transient Response
VOUT
200mV/div
2A
IOUT
1A
1A
IOUT
0A
VIN = 12V
VIN = 12V
100µs/div
100µs/div
Innovative PowerTM
ACT4072-008
ACT4072-007
VOUT
200mV/div
-9-
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Copyright © 2008 Active-Semi, Inc.
ACT4072
Active-Semi
Rev2, 27-May-08
PACKAGE OUTLINE
SOP-8 PACKAGE OUTLINE AND DIMENSIONS
D
C
E1
E
L
SYMBOL
?
θ
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
A
A2
B
A1
e
DIMENSION IN
MILLIMETERS
e
1.270 TYP
0.050 TYP
L
0.400
1.270
0.016
0.050
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
[email protected] 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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