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ACT4060A
Rev 0, 28-Apr-09
Wide Input 2A Step Down Converter FEATURES
* * * * * * * * * *
2A Output Current Up to 96% Efficiency 4.5V to 24V Input Range 10A Shutdown Supply Current 400kHz Switching Frequency Adjustable Output Voltage Cycle-by-Cycle Current Limit Protection Thermal Shutdown Protection Frequency FoldBack at Short Circuit Stability with Wide Range of Capacitors, Including Low ESR Ceramic Capacitors
GENERAL DESCRIPTION
The ACT4060A is a current-mode step-down DC/DC converter that provides up to 2A of output current at 400kHz switching frequency. The device utilizes Active-Semi's proprietary high voltage process for operation with input voltages up to 24V. The ACT4060A provides fast transient response and eases loop stabilization while providing excellent line and load regulation. This device features a very low ON-resistance power MOSFET which provides peak operating efficiency up to 96%. In shutdown mode, the ACT4060A consumes only 10A of supply current. This device also integrates protection features including cycle-by-cycle current limit, thermal shutdown and frequency fold-back at short circuit. The ACT4060A is available in a SOP-8 package and requires very few external devices for operation.
* SOP-8 Package
APPLICATIONS
* * * * * * *
TFT LCD Monitors Portable DVDs Car-Powered or Battery-Powered Equipments Set-Top Boxes Telecom Power Supplies DSL and Cable Modems and Routers Termination Supplies
TYPICAL APPLICATION CIRCUIT
Up to 24V
BS IN EN G SW
2.5V/2A
ACT4060A
ENABLE FB COMP
+
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ACT4060A
ORDERING INFORMATION
PART NUMBER
ACT4060ASH ACT4060ASH-T
Rev 0, 28-Apr-09
TEMPERATURE RANGE
-40C to 85C -40C to 85C
PACKAGE
SOP-8 SOP-8
PINS
8 8
PACKING
TUBE TAPE & REEL
PIN CONFIGURATION
SOP-8
PIN DESCRIPTIONS
PIN
1 2 3 4 5 6 7 8
NAME
BS IN SW G FB COMP EN N/C
DESCRIPTION
Bootstrap. This pin acts as the positive rail for the high-side switch's gate driver. Connect a 10nF capacitor between BS and SW. Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in the Application Information section. Switch Output. Connect this pin to the switching end of the inductor. Ground. Feedback Input. The voltage at this pin is regulated to 1.293V. Connect to the resistor divider between output and ground to set output voltage. Compensation Pin. See Stability Compensation in the Application Information section. Enable Input. When higher than 1.3V, this pin turns the IC on. When lower than 0.7V, this pin turns the IC off. Output voltage is discharged when the IC is off. When left unconnected, EN is pulled up to 4.5V with a 2A pull-up current. Not Connected.
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ACT4060A
ABSOLUTE MAXIMUM RATINGS
PARAMETER
IN Supply Voltage SW Voltage BS Voltage EN, FB, COMP Voltage Continuous SW Current Junction to Ambient Thermal Resistance (JA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 sec)
Rev 0, 28-Apr-09
VALUE
-0.3 to 28 -1 to VIN + 1 VSW - 0.3 to VSW + 8 -0.3 to 6 Internally Limited 105 0.76 -40 to 150 -55 to 150 300
UNIT
V V V V A C/W W C C 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 = 25C, unless otherwise specified.)
PARAMETER
Input Voltage Feedback Voltage High-Side Switch On Resistance Low-Side Switch On Resistance SW Leakage Current Limit COMP to Current Limit Transconductance Error Amplifier Transconductance Error Amplifier DC Gain Switching Frequency Short Circuit Switching Frequency Maximum Duty Cycle Minimum Duty Cycle Enable Threshold Voltage Enable Pull-Up Current Supply Current in Shutdown IC Supply Current in Operation Thermal Shutdown Temperature
SYMBOL
VIN VFB RONH RONL
TEST CONDITIONS
VOUT = 3.3V, ILOAD = 0A to 1A 4.5V VIN 24V, VCOMP = 1.5V
MIN
4.5 1.267
TYP
1.293 0.18 4.5
MAX
24 1.319
UNIT
V V
VEN = 0 ILIM GCOMP GEA AVEA fSW VFB = 0 DMAX VFB = 1.1V VFB = 1.4V Hysteresis = 0.1V Pin pulled up to 4.5V typically when left unconnected VEN = 0 VEN = 3V, VFB = 1.4V Hysteresis = 10C 0.7 350 VIN = 12V, VOUT = 5V ICOMP = 10A 2.4
0 2.85 1.8 650 4000 400 60 95
10
A A A/V A/V V/V
450
kHz kHz %
0 1 2 10 0.55 160 20 1.3
% V A A mA C
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ACT4060A
FUNCTIONAL BLOCK DIAGRAM
IN EN
ENABLE REGULATOR & REFERENCE
Rev 0, 28-Apr-09
BS
CURRENT SENSE AMPLIFIER
COMP
1.293V
+
ERROR AMPLIFIER
+
+
FB
FOLDBACK CONTROL OSCILLATOR & RAMP
-
PWM COMP
+
-
0.18 HIGH-SIDE POWER SWITCH
SW
LOGIC 4.5 LOW-SIDE POWER SWITCH
THERMAL SHUTDOWN
G
FUNCTIONAL DESCRIPTION
As seen in Functional Block Diagram, the ACT4060A 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 the 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 output. This state continues until the cycle starts again. The High-Side Power Switch is driven by logic using BS 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 FB input and the internal 1.293V 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 400kHz. However, if FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a typical value of 60kHz at VFB = 0.5V.
Shutdown Control
The ACT4060A has an enable input EN for turning the IC on or off. When EN is less than 0.7V, the IC is in 10A low current shutdown mode and 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 2A current source and can be left unconnected for always-on operation. Note that EN is a low voltage input with a maximum voltage of 6V, it should never be directly connected to IN.
Thermal Shutdown
The ACT4060A automatically turns off when its junction temperature exceeds 160C.
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ACT4060A
APPLICATIONS INFORMATION
Output Voltage Setting
Figure 1: Output Voltage Setting
VOUT ACT4060A
FB RFB2 RFB1
Rev 0, 28-Apr-09
Input Capacitor
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 large current flows in and out of this capacitor during switching, its ESR also affects efficiency. The input capacitance needs to be higher than 10F. 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 the shortest traces possible. In the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1F ceramic capacitor is placed right next to the IC.
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 10k and determine RFB1 from the following equation:
V R FB1 = R FB 2 OUT - 1 1.293V
(1)
Output Capacitor
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
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:
+
VIN 28 x fSW LC OUT
2
(3)
L=
VOUT x (VIN - VOUT ) VIN fSW IOUTMAX K RIPPLE
(2)
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 = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum output current. With this inductor value, the peak inductor current is IOUT x (1 + KRIPPLE/2). Make sure that this peak inductor current is less that the 3A current limit. Finally, select the inductor core size so that it does not saturate at 3A. Typical inductor values for various output voltages are shown in Table 1. Table 1: Typical Inductor Values VOUT
L
where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR 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. Therefore, a lower capacitance value can be used for ceramic type. In the case of tantalum or electrolytic capacitors, the ripple is dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR. For ceramic output capacitor, typically choose a capacitance of about 22F. For tantalum or electrolytic capacitors, choose a capacitor with less than 50m ESR.
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 a reverse voltage rating higher than the maximum input voltage.
1.5V
6.8H
1.8V
6.8H
2.5V
10H
3.3V
15H
5V
22H
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ACT4060A
STABILITY COMPENSATION
Figure 2: Stability Compensation 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:
C COMP = 1 .8 x 10 -5 R COMP
Rev 0, 28-Apr-09
(F)
(10)
If RCOMP is limited to 15k, then the actual cross over frequency is 3.4 / (VOUTCOUT). Therefore:
CCOMP = 1.2 x10 -5 VOUTCOUT
(F)
(11)
: CCOMP2 is needed only for high ESR output capacitor
The feedback loop 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 .3V AVDC = AVEA GCOMP (4) I OUT The dominant pole P1 is due to CCOMP: G EA fP1 = 2 A VEA C COMP The second pole P2 is the output pole:
fP 2 = I OUT 2 V OUT C OUT
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:
1.1 x 10 -6 RESRCOUT Min ,0.012 x VOUT () C OUT
And the proper value for CCOMP2 is:
(12)
CCOMP2 =
COUT RESRCOUT RCOMP
(13)
(5)
Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, 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:
(6)
The first zero Z1 is due to RCOMP and CCOMP:
fZ1 =
1 2 R COMP C COMP
(7)
Typical Compensation for Different Output Voltages and Output Capacitors VOUT
2.5V 3.3V 5V 2.5V 3.3V 5V 2.5V 3.3V 5V
And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used):
fP 3 = 1 2 R COMP C COMP2
COUT
22F Ceramic 22F Ceramic 22F Ceramic 47F SP CAP 47F SP CAP 47F SP CAP 470F/6.3V/30m 470F/6.3V/30m 470F/6.3V/30m
RCOMP
8.2k 12k 15k 15k 15k 15k 15k 15k 15k
CCOMP CCOMP2
2.2nF 1.5nF 1.5nF 1.5nF 1.8nF 2.7nF 15nF 22nF 27nF None None None None None None 1nF 1nF None
(8)
The following steps should be used to compensate the IC: STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP:
R COMP =
2 VOUT C OUT f SW 10 G EA GCOMP x 1 .3V
() (9)
: CCOMP2 is needed for high ESR output capacitor. Figure 3 shows an example ACT4060A application circuit generating a 2.5V/2A output.
= 1.7 x 10 8 VOUT C OUT
but limit RCOMP to 15k maximum.
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ACT4060A
Figure 3: ACT4060A 3.3V/2A Output Application
Rev 0, 28-Apr-09
VIN
Up to 24V
BS IN
C3 L1
ENABLE
EN G
IC1 ACT4060A
COMP
SW
R1
VOUT
FB
+
C1
C2 C5 (OPTIONAL)
R2
D1
C4
R3
: 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.
Table 3: ACT4060A Bill of Materials (Apply for 3.3V Output Application) ITEM
1 IC, ACT4060A 15H 20%, ISAT = 2.7A, IDC = 2.4A@ T = 40C 2 15H 10%, ISAT = 2.88A, IDC = 2.47A@ T = 40C 10H 20%, ISAT = 3.4A, IDC = 2.5A@T = 40C 10H 10%, ISAT = 2.95A, IDC = 2.3A@ T = 40C 3 4 5 6 7 8 9 10 11 Schottky Diode SK34/40V, 3A, SMB Schottky Diode B340C/40V, 3A, SMB Ceramic cap 10F/35V, X7R, 1210 Ceramic cap 2.2nF/6.3V, X7R, 0603 Ceramic cap 10nF/50V, X7R, 0603 Ceramic cap 22F/10V, X7R, 1210 SP cap 47F/6.3V, 50m Ceramic cap 220pF/6.3V, X7R, 0603 Resistor, 15.5k, 1/16W, 1%, 0603 Resistor, 10k, 1/16W, 1%, 0603 Resistor, 12k, 1/16W, 5%, 0603 FengHua, Neohm, Yageo 1
DESCRIPTION
MANUFACTURER
Active-Semi Taiyo Yuden NR 8040T 150M Wurth Electronik 744776115 Taiyo Yuden NR 6045T 100M Wurth Electronik 74477510 Transys electronics Diodes Inc Murata, TDK,Taiyo Yuden Murata, TDK,Taiyo Yuden Murata, TDK,Taiyo Yuden Murata, TDK,Taiyo Yuden Kemet, Panasonic Murata, TDK,Taiyo Yuden
QTY
1
REFERENCE
U1
1
L1
1 1 1 1 1 1 1
D1 C1 C2 C3 C4 C5 (OPTIONAL) R1 R2 R3
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ACT4060A
Figure 4: ACT4060A 5V/2A Output Application
Rev 0, 28-Apr-09
VIN
Up to 24V
BS IN
C3 L1
ENABLE
EN G
IC1 ACT4060A
COMP
SW
R1
VOUT
FB
+
C1
C2 C5 (OPTIONAL)
R2
D1
C4
R3
: 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.
Table 4: ACT4060A Bill of Materials (Apply for 5V Output Application) ITEM
1 2 3 4 5 6 7 8 9 10 11 IC, ACT4060A 15H 20%, ISAT =2.7A, IDC = 2.4A@ T = 40C Schottky Diode SK34/40V, 3A, SMB Schottky Diode B340C/40V, 3A, SMB Ceramic cap 10F/35V, X7R, 1210 Ceramic cap 2.2nF/6.3V, X7R, 0603 Ceramic cap 10nF/50V, X7R, 0603 Ceramic cap 22F/10V, X7R, 1210 SP cap 47F/6.3V, 50m Ceramic cap 220pF/6.3V, X7R, 0603 Resistor, 28.7k, 1/16W, 1%, 0603 Resistor, 10k, 1/16W, 1%, 0603 Resistor, 15k, 1/16W, 5%, 0603 FengHua, Neohm, Yageo 1
DESCRIPTION
MANUFACTURER
Active-Semi Taiyo Yuden NR 8040T 150M Transys electronics Diodes Inc Murata, TDK, Taiyo Yuden Murata, TDK, Taiyo Yuden Murata, TDK, Taiyo Yuden Murata, TDK, Taiyo Yuden Kemet, Panasonic Murata, TDK, Taiyo Yuden
QTY
1 1 1 1 1 1 1 1
REFERENCE
U1 L1 D1 C1 C2 C3 C4 C5 (OPTIONAL) R1 R2 R3
15H 10%, ISAT = 2.88A, IDC = 2.47A@ T = 40C Wurth Electronik 744776115
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ACT4060A
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 3, unless otherwise specified.)
Rev 0, 28-Apr-09
Efficiency vs. Output Current
100 90 80 VOUT = 2.5V VIN = 7V 100 90 80 ACT4060A-001
Efficiency vs. Output Current
ACT4060A-002 VOUT = 5V
VIN = 7V VIN = 12V
Efficiency (%)
60 50 40 30 20 10 0 10
VIN = 12V
Efficiency (%)
70
70 60 50 40 30 20 10 0
100
1000
10000
10
100
1000
10000
Output Current (mA)
Output Current (mA)
Efficiency vs. Output Current
100 5000
Maximum Output Current vs. Duty Cycle Maximum Output Current (mA)
ACT4060A-003 ACT4060A-004
80 VIN = 5V
4000
Efficiency (%)
60
VIN = 12V
3000
40
2000
20 VOUT = 3.3V 10 100 1000 10000
1000
0
0 0 20 40 60 80 100
Output Current (mA)
Duty Cycle (% )
Switching Frequency vs. Input Voltage
410 1.33 ACT4060A-005
Feedback Voltage vs. Temperature
ACT4060A-006
Switching Frequency (kHz)
405
Feedback Voltage (V)
1.31
400 395 390 385 380 4
1.29
1.27
VOUT = 2.5V IOUT = 1A 1.25 6 8 10 12 14 16 18 20 -50 0 50 100 150
Input Voltage (V)
Temperature (C)
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ACT4060A
TYPICAL PERFORMANCE CHARACTERISTICS CONT'D
(Circuit of Figure 3, unless otherwise specified.)
Rev 0, 28-Apr-09
Shutdown Current vs. Input Voltage
25 ACT4060A-007
Shutdown Current (A)
20
15
10
5
0 5 10 15 20 25
Input Voltage (V)
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ACT4060A
PACKAGE OUTLINE
SOP-8 PACKAGE OUTLINE AND DIMENSIONS
C D
Rev 0, 28-Apr-09
SYMBOL
A A1 A2 B C
e B
DIMENSION IN MILLIMETERS MIN
1.350 0.100 1.350 0.330 0.190 4.700 3.800 5.800
DIMENSION IN INCHES MIN
0.053 0.004 0.053 0.013 0.007 0.185 0.150 0.228
MAX
1.750 0.250 1.550 0.510 0.250 5.100 4.000 6.300
MAX
0.069 0.010 0.061 0.020 0.010 0.201 0.157 0.248
D E E1 e L
1.270 TYP 0.400 0 1.270 8
0.050 TYP 0.016 0 0.050 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 lifesupport 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@activesemi.com or visit http://www.active-semi.com. For other inquiries, please send to: 2728 Orchard Parkway, San Jose, CA 95134-2012, USA
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