ACTIVE-SEMI ACT4065

Data Sheet
Rev 2, 6/2006
ACT4065
High Input 2A Step Down Converter
FEATURES
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GENERAL DESCRIPTION
The ACT4065 is a current-mode step-down
DC-DC converter that generates up to 2A output
current at 200kHz switching frequency. The
device
utilizes
Active-Semi’s
proprietary
ISOBCD30 process for operation with input
voltage up to 28V.
2A Output Current
Up to 95% Efficiency
Up to 28V Input Range
8µA Shutdown Supply Current
200kHz 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
SOP-8 Package
Consuming only 8μA in shutdown mode, the
ACT4065 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.
The ACT4065 is available in SOP-8 package
and requires very few external devices for
operation.
APPLICATIONS
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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
5V/2A (<23V INPUT)
5V/1.7A (>23V INPUT)
5V/1.7A
BS
8.5V to 28V
IN
SW
ACT4065
ENABLE
EN
G
FB
COMP
+
Figure 1. Typical Application Circuit
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ACT4065
ORDERING INFORMATION
PART NUMBER
ACT4065SH
ACT4065SH-T
TEMPERATURE RANGE
-40°C to 85°C
-40°C to 85°C
PACKAGE
SOP-8
SOP-8
PINS
8
8
PACKING
TUBE
TAPE & REEL
PIN CONFIGURATION
BS
1
IN
2
SW
3
G
4
ACT4065SH
8
N/C
7
EN
6
COMP
5
FB
SOP-8
PIN DESCRIPTION
PIN NUMBER
PIN NAME
1
BS
2
IN
3
4
SW
G
5
FB
6
COMP
7
EN
8
N/C
Active-Semi, Inc.
PIN DESCRIPTION
Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver.
Connect a 10nF between this pin and SW.
Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in
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 Compensation Technique in 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. 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.
Not Connected.
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ACT4065
ABSOLUTE MAXIMUM RATINGS
(Note: Exceeding these limits may damage the device. Exposure to absolute maximum rating conditions for long periods may affect device
reliability.)
PARAMETER
IN Supply Voltage
SW Voltage
BS Voltage
EN, FB, COMP Voltage
Continuous SW Current
Maximum Power Dissipation
VALUE
-0.3 to 30
-1 to VIN + 1
VSW – 0.3 to VSW + 8
-0.3 to 6
Internally limited
0.76
UNIT
V
V
V
V
A
W
105
°C/W
-40 to 150
-55 to 150
300
°C
°C
°C
Junction to Ambient Thermal Resistance (θ JA)
Operating Junction Temperature
Storage Temperature
Lead Temperature (Soldering, 10 sec)
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TJ = 25°C 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
Active-Semi, Inc.
SYMBOL
TEST CONDITIONS
VIN
VOUT = 5V, ILOAD = 1A
VFB
VCOMP = 1.5V
RONH
RONL
VEN = 0
ILIM
MIN
6
1.267
3
GCOMP
GEA
AVEA
fSW
DMAX
ΔICOMP = ±10µA
160
VFB = 0
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 = 10°C
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0.7
TYP
1.293
0.2
8
0
3.5
MAX
28
1.319
10
UNIT
V
V
Ω
Ω
µA
A
1.8
A/V
550
4000
200
50
93
µA/V
V/V
kHz
kHz
%
%
V
240
0
1.3
1
1
µA
8
0.7
160
20
µA
mA
°C
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ACT4065
IN
2μA
EN
COMP
ENABLE
REGULATOR
&
REFERENCE
BS
CURRENT SENSE
AMPLIFIER
ERROR
AMPLIFIER
–
+
1.293V
+
–
FB
FOLDBACK
CONTROL
+
OSCILLATOR
&
RAMP
–
+
–
PWM
COMPARATOR
0.2Ω
HIGH-SIDE
POWER
SWITCH
SW
LOGIC
8Ω LOW-SIDE
POWER SWITCH
THERMAL
SHUTDOWN
G
Figure 2. Functional Block Diagram
Side Power Switch turns on.
FUNCTIONAL DESCRIPTION
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.
As seen in Figure 2, Functional Block
Diagram, the ACT4065 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 HighSide 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 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 output. This
state continues until the cycle starts again.
The Oscillator normally switches at 200kHz.
However, if FB voltage is less than 0.7V, then the
switching frequency decreases until it reaches a
minimum of 50kHz at VFB = 0.5V.
SHUTDOWN CONTROL
The ACT4065 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 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. Note that
EN is a low voltage input with a maximum
voltage of 6V; it should never be directly
connected to IN.
The High-Side Power Switch is driven by
logic using BS bootstrap pin as the positive rail.
This pin is charged to VSW + 6V when the Low-
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THERMAL SHUTDOWN
The ACT4065 automatically turns off when its
junction temperature exceeds 160°C.
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ACT4065
APPLICATION 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 large
current flows in and out of this capacitor during
switching, its ESR also affects efficiency.
OUTPUT VOLTAGE SETTING
VOU T
RFB 1
ACT4065
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 traces possible. 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.
FB
RFB 2
Figure 3. Output Voltage Setting
Figure 3 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:
RFB1
 V

= R FB2  OUT − 1 
 1.293 V

OUTPUT CAPACITOR
The output capacitor also needs to have low
ESR to keep low output voltage ripple. The
output ripple voltage is:
(1)
VRIPPLE = I OUTMAX K RIPPLE R ESR
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 )
+
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.
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
L
10μH
10μH
15μH 22μH 33μH
Active-Semi, Inc.
3.3V
(3)
For ceramic output type, typically choose a
capacitance of about 22µF. For tantalum or
electrolytic type, 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 3A current limit. Finally, select the inductor
core size so that it does not saturate at 3A.
VOUT
28 • f SW 2 LCOUT
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 in 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.
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.
(2)
VIN fSW IOUTMAX K RIPPLE
VIN
5V
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ACT4065
frequency. If RCOMP is less than 15kΩ, the
equation for CCOMP is:
STABILITY COMPENSATION
COMP
ACT4065
CCOMP =
CC O MP
(F )
(10)
If RCOMP is limited to 15kΩ, then the actual cross
over frequency is 6.1 / (VOUTCOUT). Therefore:
*
RC O MP
1.6 × 10 − 5
RCOMP
CC O MP 2
CCOMP = 6.96 × 10 − 6VOUT COUT
Figure 4. Stability Compensation
The feedback system of the IC is stabilized
by the components at COMP pin, as shown in
Figure 4. The DC loop gain of the system is
determined by the following equation:
1.293V
AVEAGCOMP
IOUT
R ESRCOUT
 1.1 × 10 − 6
≥ Min
,0.012 • VOUT
 COUT
(4)
The dominant pole P1 is due to CCOMP:
fP1 =
G EA
CCOMP 2 =
The second pole P2 is the output pole:
fP 2 =
IOUT
The first zero Z1 is due to RCOMP and CCOMP:
fZ 1 =
1
2πRCOMP CCOMP
(7)
IC:
1
2πRCOMP CCOMP 2
VOUT
2.5V
3.3V
5V
2.5V
3.3V
5V
2.5V
3.3V
5V
(8)
STEP 1. Set the cross over frequency at 1/5 of
the switching frequency via RCOMP:
2πVOUT COUT fSW
10GEAGCOMP • 1.293V
= 9.8 × 10 7 VOUT COUT
(Ω )
COUT RESRCOUT
(13)
RCOMP
Table 2. Typical Compensation for Different
Output Voltages and Output Capacitors
Follow the following steps to compensate the
RCOMP =
(12)
Table 2 shows some calculated results based
on the compensation method above.
And finally, the third pole is due to RCOMP and
CCOMP2 (if CCOMP2 is used):
fP 3 =
(Ω)
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.
(6)
2πVOUT COUT




And the proper value for CCOMP2 is:
(5)
2 πAVEA CCOMP
(11)
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:
*CCOMP2 is needed only for high ESR output capacitor
AVDC =
(F )
(9)
COUT
RCOMP
22μF Ceramic
5.6kΩ
22μF Ceramic
7.2kΩ
22μF Ceramic
10kΩ
47μF SP Cap
11kΩ
47μF SP Cap
15kΩ
47μF SP Cap
15kΩ
470μF/6.3V/30mΩ 15kΩ
470μF/6.3V/30mΩ 15kΩ
470μF/10V/30mΩ 15kΩ
CCOMP
2.7nF
2.2nF
1.5nF
1.5nF
1nF
1.5nF
8.2nF
10nF
15nF
CCOMP2
None
None
None
None
None
None
1nF
1nF
None
Figure 5 shows a sample ACT4065
application circuit generating 2.5V/2A output.
but limit RCOMP to 15kΩ maximum.
STEP 2. Set the zero fZ1 at 1/4 of the cross over
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ACT4065
C3
10nF
BS
6V to 25V
IN
IC1
ACT4065
ENABLE
EN
2.5V/2A
R1 12 K
FB
G
+
L1 15 μH/3A
SW
C1
10μF/35V
COMP
C2
2.7nF
R3
5.6k
R2
13k
D1
C4
22μF/10V
Ceramic
C5
(OPTIONAL)
Figure 5. ACT4065 2.5V/2A Output Application
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ACT4065
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 5, unless otherwise specified .)
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ACT4065
PACKAGE OUTLINE
SOP-8 PACKAGE OUTLINE AND DIMENSIONS
SYMBOL
A
A1
A2
B
C
D
E
E1
e
L
θ
DIMENSION IN
MILLIMETERS
MIN
MAX
1.350 1.750
0.100 0.250
1.350 1.550
0.330 0.510
0.190 0.250
4.780 5.000
3.800 4.000
5.800 6.300
1.270 TYP
0.400 1.270
0°
8°
DIMENSION IN
INCHES
MIN
MAX
0.053 0.069
0.004 0.010
0.053 0.061
0.013 0.020
0.007 0.010
0.188 0.197
0.150 0.157
0.228 0.248
0.050 TYP
0.016 0.050
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 data sheet, 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 www.active-semi.com. For other inquiries, please send to:
1270 Oakmead Parkway, Sunnyvale, California 94085, USA
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