ACTIVE-SEMI ACT4065A

ACT4065A
®
Rev 0, 23-Apr-12
High Input 2A Step Down Converter
FEATURES
GENERAL DESCRIPTION
•
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•
•
•
•
•
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The ACT4065A is a current-mode step-down
DC/DC converter that generates up to 2A output
current at 210kHz switching frequency.
2A Output Current
Up to 95% Efficiency
6.0V to 30V Input Range
The ACT4065A is highly efficient with peak efficiency at 95% when in operation. Protection features include cycle-by-cycle current limit, thermal
shutdown, and frequency foldback at short circuit.
210kHz Switching Frequency
Adjustable Output Voltage
Cycle-by-Cycle Current Limit Protection
The ACT4065A is available in SOP-8 package and
requires very few external devices for operation.
Thermal Shutdown Protection
Frequency Foldback at Short Circuit
Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
Note: ACT4065A is the drop-in replacement for
ACT4065 with feedback resistance value change.
• 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
Efficiency vs. Load current
ACT4065A-001
95
VIN = 12V
Efficiency (%)
90
85
VIN = 24V
80
75
VOUT = 5V
70
10
100
1000
10000
Load Current (mA)
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Copyright © 2012 Active-Semi, Inc.
ACT4065A
®
Rev 0, 23-Apr-12
ORDERING INFORMATION
PART NUMBER
TEMPERATURE RANGE
PACKAGE
PINS
PACKING
ACT4065ASH-T
-40°C to 85°C
SOP-8
8
TAPE & REEL
PIN CONFIGURATION
SOP-8
PIN DESCRIPTION
PIN NUMBER PIN NAME
PIN DESCRIPTION
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 0.808V. Connect to the resistor
divider between output and ground to set output voltage.
6
COMP
Compensation Pin. See Compensation Techniques in Application Information section.
7
EN
Enable Input. When higher than 0.8V, this pin turns the IC on. When lower than 0.8V,
this pin turn the IC off. Output voltage is discharged when the IC is off. This pin has a
small internal pull-up current to a high level voltage when pin is not connected. Do not
allow EN pin to exceed 6V.
8
N/C
Not Connected.
Innovative PowerTM
Switch Output. Connect this pin to the switching end of the inductor.
-2-
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Copyright © 2012 Active-Semi, Inc.
ACT4065A
®
Rev 0, 23-Apr-12
ABSOLUTE MAXIMUM RATINGSc
PARAMETER
VALUE
UNIT
-0.3 to 30
V
SW Voltage
-1 to VIN + 1
V
BS Voltage
VSW - 0.3 to VSW + 7
V
EN, FB, COMP Voltage
-0.3 to 6
V
Continuous SW Current
Internally limited
A
Maximum Power Dissipation
0.76
W
Junction to Ambient Thermal Resistance (θJA )
105
°C/W
Operating Junction Temperature
-40 to 150
°C
Storage Temperature
-55 to 150
°C
300
°C
IN Supply Voltage
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, TJ = 25˚C, unless otherwise specified.)
PARAMETER
SYMBOL
TEST CONDITIONS
Input Voltage
VIN
VOUT = 5V, ILOAD = 1A
Feedback Voltage
VFB
VCOMP = 1.5V
MIN
TYP
6
0.792
0.808
MAX
UNIT
30
V
0.824
V
High-Side Switch On Resistance
RONH
0.22
Ω
Low-Side Switch On Resistance
RONL
8
Ω
SW Leakage
High-Side Switch Current Limit
VEN = 0
ILIM
COMP to Current Limit Transconductance
GCOMP
Error Amplifier Transconductance
GEA
Error Amplifier DC Gain
AVEA
Switching Frequency
Maximum Duty Cycle
Duty = 50%
ΔICOMP = ±10µA
fSW
Short Circuit Switching Frequency
DMAX
1
190
10
µA
3.5
A
3.4
A/V
650
µA/V
4000
V/V
210
240
kHz
VFB = 0
30
kHz
VFB = 0.7V
88
%
Minimum Duty Cycle
VFB = 1.0V
Enable Threshold Voltage
Hysteresis = 0.1V
Enable Pull-Up Current
Pin pulled up to 4.5V typically
when left unconnected
4
Supply Current in Shutdown
VEN = 0
75
IC Supply Current in Operation
VEN = 3V, VFB = 1.0V
0.75
mA
Thermal Shutdown Temperature
Hysteresis = 10°C
155
°C
Innovative PowerTM
-3-
0.75
0.8
0
%
0.85
V
µA
100
µA
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Copyright © 2012 Active-Semi, Inc.
ACT4065A
®
Rev 0, 23-Apr-12
FUNCTIONAL BLOCK DIAGRAM
is charged to VSW + 5V when the Low-Side Power
Switch turns on.
FUNCTIONAL DESCRIPTION
As seen in, Functional Block Diagram, the ACT4065A is a current mode pulse width modulation
(PWM) converter. The converter operates as follows:
The COMP voltage is the integration of the error
between the FB input and the internal 0.808V 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 2.0V.
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 Oscillator normally switches at 210kHz. However, if the FB voltage is less than 0.6V, then the
switching frequency decreases until it reaches a
minimum of 30kHz at VFB = 0.15V.
Shutdown Control
The ACT4065A has an enable input EN for turning
the IC on or off. When EN is less than 0.7V, the IC
is in 8μA low current shutdown mode . When EN is
higher than 0.8V, the IC is in normal operation
mode. EN is internally pulled up with a 4μA current
source and can be left unconnected for always-on
operation. EN should never be directly connected to
IN.
Thermal Shutdown
The High-Side Power Switch is driven by logic using the BS bootstrap pin as the positive rail. This pin
Innovative PowerTM
The ACT4065A automatically turns off when its
junction temperature exceeds 155°C.
-4-
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Copyright © 2012 Active-Semi, Inc.
ACT4065A
®
Rev 0, 23-Apr-12
APPLICATIONS INFORMATION
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 a large current flows in and out of
this capacitor during switching, its ESR also affects
efficiency.
Output Voltage Setting
Figure 1:
Output Voltage Setting
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 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 Capacitor
RFB1
⎛ V
⎞
= RFB 2 ⎜ OUT − 1 ⎟
⎝ 0.808V
⎠
The output capacitor also needs to have low ESR to
keep low output voltage ripple. The output ripple
voltage is:
(1)
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 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 (Table 1), the peak inductor
current is IOUT × (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.
⎛
VIN
VRIPPLE = IOUTMAXK RIPPLERESR + ⎜⎜
2
⎝ 28 × fSW LCOUT
⎞
⎟ (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, 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 type, 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 type, typically choose a
capacitance of about 22µF. For tantalum or
electrolytic type, choose a capacitor with less than
50mΩ ESR.
Rectifier Diode
Use a Schotky 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
VOUT
1.5V
1.8V
2.5V
3.3V
5V
L
10μH
10μH
15μH
22μH
33μH
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Copyright © 2012 Active-Semi, Inc.
ACT4065A
®
Rev 0, 23-Apr-12
frequency. If RCOMP is less than 15kΩ, the equation
for CCOMP is:
Stability compensation
Figure 2:
Stability Compensation
=
C COMP
−5
1 . 8 × 10
R COMP
(10)
(F)
If RCOMP is limited to 15kΩ, then the actual cross
over frequency is 6.1/ (VOUTCOUT). Therefore:
C COMP = 1 . 2 × 10 5 V OUT C OUT
The feedback system of the IC is stabilized by the
components at COMP pin, as shown in Figure 2.
The DC loop gain of the system is determined by
the following equation:
A VDC
(4)
⎞
⎛ 1.1 × 10 −6
RESROUT ≥ Min⎜⎜
,0.012VOUT ⎟⎟
⎠
⎝ COUT
fP1
CCOMP 2 =
(5)
I OUT
2 π VOUT C OUT
1
Typical Compensation for Different Output voltages and Output Capacitors
And finally, the third pole is due to RCOMP and
CCOMP2 (if CCOMP2 is used):
fP 3 =
1
(8)
2π R COMP C COMP2
Follow the following steps to compensate the IC:
STEP 1. Set the cross over frequency at 1/5 of the
switching frequency via RCOMP:
R COMP =
2 π V OUT C OUT f SW
10 G EA G COMP × 0 . 808 V
= 2 . 75 × 10 8 V OUT C OUT
(Ω)
(9)
CCOMP2c
VOUT
COUT
2.5V
22μF Ceramic
12kΩ
2.2nF
None
3.3V
22μF Ceramic
12kΩ
1.5nF
None
5V
22μF Ceramic
15kΩ
2.2nF
None
2.5V
47μF SP Cap
15kΩ
1.5nF
None
3.3V
47μF SP Cap
15kΩ
1.8nF
None
5V
47μF SP Cap
15kΩ
2.7nF
None
2.5V
470µF/6.3V/30mΩ
15kΩ
1.5nF
47pF
3.3V
470µF/6.3V/30mΩ
15kΩ
2.2nF
47pF
5V
470µF/10V/30mΩ
15kΩ
2.7nF
47pF
RCOMP CCOMP
c: CCOMP2 is needed only for high ESR output capacitors
but limit RCOMP to 15kΩ maximum.
Figure 3 shows a sample ACT4065A application
circuit generating a 2.5V/2A output.
STEP 2. Set the zero fZ1 at 1/4 of the cross over
Innovative PowerTM
(13)
Table 2:
(7)
2π RCOMP CCOMP
COUT R ESROUT
RCOMP
Table 2 shows some calculated results based on the
compensation method above.
(6)
The first zero Z1 is due to RCOMP and CCOMP:
f Z1 =
(12)
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.
The second pole P2 is the output pole:
fP 2 =
(Ω)
And the proper value for CCOMP2 is:
The dominant pole P1 is due to CCOMP:
G EA
=
2 π AVEA C COMP
(11)
STEP 3. If the output capacitors 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
required. The condition for using CCOMP2 is:
c: CCOMP2 is needed only for high ESR output capacitors
0 . 808 V
=
A VEA G COMP
I OUT
(F)
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Copyright © 2012 Active-Semi, Inc.
ACT4065A
®
Rev 0, 23-Apr-12
Figure 3:
Typical Application Circuit for 5V/2A Car Charger
Table 3:
BOM List for 5V/2A Car Charger
ITEM
REFERENCE
1
U1
IC, ACT4065ASH, SOP-8EP
Active-Semi
1
2
C1
Capacitor, Electrolytic, 47µF/35V, 6.3х7mm
Murata, TDK
1
3
C2
Capacitor, Ceramic, 10µF/35V, 1210, SMD
Murata, TDK
1
4
C3
Capacitor, Ceramic, 2.2nF/6.3V, 0603, SMD
Murata, TDK
1
5
C4
Capacitor, Ceramic, 10nF/50V, 0603, SMD
Murata, TDK
1
6
C5
Capacitor, Electrolytic, 100µF/10V, 6.3х7mm
Murata, TDK
1
7
C6
Capacitor, Ceramic, 1µF/10V, 0603, SMD
Murata, TDK
1
8
L1
Inductor,33µH, 3.0A
Sumida
1
9
D1
Diode, Schottky, 40V/2A, SB240
Diodes
1
10
R1
Chip Resistor, 52kΩ, 0603, 1%
Murata, TDK
1
11
R3
Chip Resistor, 8.2kΩ, 0603, 5%
Murata, TDK
1
12
R2
Chip Resistor, 10kΩ, 0603, 1%
Murata, TDK
1
Innovative PowerTM
DESCRIPTION
-7-
MANUFACTURER
QTY
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Copyright © 2012 Active-Semi, Inc.
ACT4065A
®
Rev 0, 23-Apr-12
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 3, unless otherwise specified .)
Switching Frequency vs. Feedback Voltage
Switching Frequency vs. Input Voltage
210
Switching Frequency (kHz)
Switching Frequency (kHz)
230
190
170
150
130
ACT4065A-003
260
ACT4065A-002
250
210
160
110
60
10
110
6
8
10
15
20
25
0
30
100
200
Maximum Peak Current vs. Duty Cycle
400
500
600
700
800
900
Start up with EN
3.7
3.6
ACT4065A-005
ACT4065A-004
3.8
Maximum CC Current (mA)
300
Feedback Voltage (mV)
Input Voltage (V)
VIN = 12V
V0UT = 5V
ILOAD = 2A
3.5
CH1
3.4
CH2
3.3
3.2
3.1
3
20
30
40
50
60
70
CH1: EN, 1V/div
CH2: VOUT, 1V/div
TIME: 10ms/div
Duty Cycle
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-8-
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Copyright © 2012 Active-Semi, Inc.
ACT4065A
®
Rev 0, 23-Apr-12
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
4.780
5.000
0.188
0.197
E
3.800
4.000
0.150
0.157
E1
5.800
6.300
0.228
0.248
e
A
A2
B
A1
e
DIMENSION IN
MILLIMETERS
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
sales@active-semi.com or visit http://www.active-semi.com.
®
is a registered trademark of Active-Semi.
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