ACTIVE-SEMI ACT4070YH

ACT4070
Rev 0, 12/2006
Wide Input 3A Step Down Converter
FEATURES
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GENERAL DESCRIPTION
3A Output Current
The ACT4070 is a current-mode step-down
DC/DC converter that generates up to 3A output
current at 400kHz switching frequency. The
device utilizes Active-Semi’s proprietary
ISOBCD30 process for operation with input
voltage up to 30V.
Up to 95% Efficiency
4.5V to 30V Input Range
6µA Shutdown Supply Current
400kHz Switching Frequency
Consuming only 6μA in shutdown mode, the
ACT4070 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 device also includes an internal soft start
function to prevent overshoot.
Adjustable Output Voltage
Cycle-by-Cycle Current Limit Protection
Thermal Shutdown Protection
Internal Soft Start Function
Frequency Fold Back at Short Circuit
The ACT4070 is available in SOP-8/EP exposed
pad package and requires very few external
devices for operation.
Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
 SOP-8/EP (Exposed Pad) 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
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ACT4070
ORDERING INFORMATION
PART NUMBER
TEMPERATURE RANGE
PACKAGE
PINS
PACKING
ACT4070YH
-40°C to 85°C
SOP-8/EP
8
TUBE
ACT4070YH-T
-40°C to 85°C
SOP-8/EP
8
TAPE & REEL
PIN CONFIGURATION
SOP-8/EP
PIN DESCRIPTION
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 output and ground to set output voltage.
6
COMP
Compensation Pin. See Compensation Technique in Application Information section.
7
EN
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.
8
N/C
Not Connected.
EP
Exposed Pad shown as dashed box. The exposed thermal pad should be connected to board ground plane and pin 4. The ground plane should include a large
exposed copper pad under the package for thermal dissipation (see package outline). The leads and exposed pad should be flush with the board, without offset
from the board surface.
EP
PIN DESCRIPTION
Switch Output. Connect this pin to the switching end of the inductor.
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ACT4070
ABSOLUTE MAXIMUM RATINGS
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)
46
°C/W
Maximum Power Dissipation
1.8
W
Operating Junction Temperature
-40 to 150
°C
Storage Temperature
-55 to 150
°C
300
°C
Continuous SW Current
Lead Temperature (Soldering, 10 sec)
: 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
TEST CONDITIONS
MIN
VIN
Feedback Voltage
VFB
1.198 1.222 1.246
V
High-Side Switch On Resistance
RONH
100
mΩ
Low-Side Switch On Resistance
RONL
10
Ω
Current Limit
VEN = 0, VIN = 12V, VSW = 0V
GCOMP
Error Amplifier Transconductance
GEA
Error Amplifier DC Gain
AVEA
3.5
ΔILOAD/ΔICOMP
ΔICOMP = ±10µA
fSW
Short Circuit Switching Frequency
30
0
ILIM
COMP to Current Limit Transconductance
Switching Frequency
4.5
MAX UNIT
Input Voltage
SW Leakage
VOUT = 2.5V, ILOAD = 0A to 3A
TYP
340
10
V
µA
5
A
3
A/V
550
µA/V
4000
V/V
400
460
kHz
VFB = 0V
40
kHz
VFB = 1.1V, PWM mode
90
%
Minimum Duty Cycle
VFB = 1.4V, PFM mode
0
%
Enable Threshold Voltage
Hysteresis = 0.1V
Enable Pull Up Current
Pin pulled up to VIN when left unconnected
2
Supply Current in Shutdown
VEN = 0
6
20
µA
IC Supply Current in Operation
VEN = 3V, not switching
0.85
2
mA
Thermal Shutdown Temperature
Hysteresis = 10°C
160
Maximum Duty Cycle
DMAX
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0.7
1
1.3
V
µA
°C
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ACT4070
FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL DESCRIPTION
As seen in the Functional Block Diagram, the
ACT4070 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 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 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-Side Power
Switch turns on.
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The COMP voltage is the integration of the error
between 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 2.65V.
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 40kHz at VFB = 0V.
Shutdown Control
The ACT4070 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 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 ACT4070 automatically turns off when its junction temperature exceeds 160°C and then restarts
once the temperature falls to 150°C.
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ACT4070
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 large current flows in and out of this
capacitor during switching, its ESR also affects efficiency.
 V

RFB1  RFB2  OUT - 1 
 1.222V 
(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 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.
Figure 1:
Output Voltage Setting
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 IOUTMAX K RIPPLE
VRIPPLE  IOUTMAX K RIPPLE RRIPPLE

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 = between 20% and
30% to correspond to the peak-to-peak ripple current
being a percentage of the maximum output current.
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.
Typical Inductor Values
2.5V
3.3V
5V
L
6.8μH
6.8μH
6.8μH
8.5μH
15μH
(3)
Rectifier Diode
Table 1:
1.8V
2
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 5A current
limit. Finally, select the inductor core size so that it
does not saturate at 5A.
1.5V
28  fSW 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)
VOUT
VIN
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ACT4070
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
CCOMP 
1.6 x10 5
RCOMP
(10)
(F)
If RCOMP is limited to 15kΩ, then the actual cross
over frequency is 4.8/(VOUTCOUT). Therefore:
CCOMP  8.8 x10 6 VOUT COUT
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:
1.222V
AVEAGCOMP
IOUT
RESROUT
 1.1x10 6

 Min
,0.012VOUT 
 COUT

(4)
The dominant pole P1 is due to CCOMP:
fP 1 
G EA
2  A VEA C COMP
CCOMP 
(5)
IOUT
2 VOUT C OUT
(6)
1
COUT R ESROUT
RCOMP
(13)
Table 2 shows some calculated results based on
the compensation method above.
(7)
2 RCOMP CCOMP
(12)
Though CCOMP2 is unnecessary when the output
capacitor has sufficiently low ESR, a small value
CCOMP2 such as 220pF may improve stability
against PCB layout parasitic effects.
The first zero Z1 is due to RCOMP and CCOMP:
fZ1 
(Ω)
And the proper value for CCOMP2 is:
The second pole P2 is the output pole:
fP 2 
(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)
Table 2:
Typical Compensation for Different Output
Voltages and Output Capacitors
And finally, the third pole is due to RCOMP and
CCOMP2 (if CCOMP2 is used):
CCOMP CCOMP2
VOUT
COUT
RCOMP
1.8V
22μF Ceramic
4kΩ
3.3nF
220pF
2.5V
22μF Ceramic
5.6kΩ
3.3nF
220pF
Follow the following steps to compensate the IC:
5V
22μF Ceramic
12kΩ
1.5nF
220pF
STEP 1. Set the cross over frequency at 1/10 of
the switching frequency via RCOMP:
1.8V
100μF SP CAP
15kΩ
1.5nF
220pF
2.5V
100μF SP CAP
15kΩ
2.2nF
220pF
5V
100μF SP CAP
15kΩ
4.7nF
220pF
fP 3 
1
(8)
2 RCOMP CCOMP2
RCOMP 
2 VOUT COUT fSW
10 GEAGCOMP 1 .222 V
 1 .25 x10 8 VOUT COUT
(Ω)
: CCOMP2 is needed for board parasitic and high ESR output
capacitor.
(9)
Figure 3 shows a sample ACT4070 application
circuit generating a 2.5V/3A output.
but limit RCOMP to 15kΩ maximum.
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ACT4070
Figure 3:
ACT4070 2.5V/3A Output Application
C3
10nF
BS
4.5V to 30V
VIN
IN
IC1
ACT4070
EN
ENABLE
G
+
C1
10µF/35V
L1 10µH/4A
SW
2.5V/3A
VOUT
R1 14k
FB
COMP
C2
(CCOMP)
3.3nF
R3
(RCOMP)
5.6k
C5
(CCOMP2)
220pF
R2
13k
D1
40V
3A
C4 (COUT)
22µF/10V
ceramic or
47µH/6.3 SP
Cap
: 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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ACT4070
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 3, unless otherwise specified.)
Efficiency vs. Output Current
Efficiency vs. Output Current
Efficiency (%)
70
60
90
VIN = 12V
50
VIN = 30V
40
VIN = 20V
30
20
0
0.01
0.1
1
70
60
VIN = 30V
50
VIN = 12V
40
30
VIN = 20V
VOUT = 2.5V
L = 10µH
CIN = 22µF
COUT = 22µF
20
VOUT = 5V
L = 15µH
CIN = 22µF
COUT = 22µF
10
VIN = 8V
80
Efficiency (%)
VIN = 8V
80
ACT4070-0002
90
100
ACT4070-0001
100
10
0
0.01
10
0.1
Output Current (A)
Feedback Voltage vs. Temperature
Switching Frequency vs. Input Voltage
1.23
Switching Frequency (kHz)
1.25
1.21
1.19
1.17
ACT4070-0004
Feedback Voltage (V)
10
500
ACT4070-0003
1.27
450
400
350
300
-40
-20
0
20
40
60
80
8
100
10
12
Temperature (°C)
14
16
18
20
22
24
26
28
30
Input Voltage (V)
Surface Temperature vs. Output Current
Shutdown Supply Current vs. Input Voltage
14
12
Surface Temperature (°C)
16
10
8
6
4
2
VOUT = 5V
L = 15µH
CIN = 22µF
COUT = 22µF
120
VIN = 30V
100
80
ACT4070-006
140
ACT4070-0005
18
Shutdown Supply Current (µA)
1
Output Current (A)
VIN = 20V
60
40
VIN = 12V
20
0
0
5
10
15
20
25
0
30
0.5
1
1.5
2
2.5
3
Output Current (A)
Input Voltage (V)
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ACT4070
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit of Figure 3, unless otherwise specified.)
Load Transient Response
Load Transient Response
ACT4070-0008
ACT4070-0007
VOUT
200mV/div
VOUT
200mV/div
1A
1A
IOUT
IOUT
0A
0A
VIN = 12V
VIN = 12V
100µs/div
100µs/div
Load Transient Response
ACT4070-0009
VOUT
200mV/div
3A
IOUT
2A
VIN = 12V
100µs/div
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ACT4070
PACKAGE OUTLINE
SOP-8/EP PACKAGE OUTLINE AND DIMENSIONS
DIMENSION IN
MILLIMETERS
DIMENSION IN
INCHES
MIN
MAX
MIN
MAX
A
1.350
1.750
0.053
0.069
A1
0.050
0.150
0.002
0.006
A2
1.350
1.550
0.053
0.061
b
0.330
0.510
0.013
0.020
c
0.170
0.250
0.007
0.010
D
4.700
5.100
0.185
0.200
D1
3.202
3.402
0.126
0.134
E
3.800
4.000
0.150
0.157
E1
5.800
6.200
0.228
0.244
E2
2.313
2.513
0.091
0.099
D
b
e
D1
SYMBOL
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
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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