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ACT4455 Schematic ( PDF Datasheet ) - Active-Semo

Teilenummer ACT4455
Beschreibung 36V/5A Step Down DC/DC Converter
Hersteller Active-Semo
Logo Active-Semo Logo 




Gesamt 15 Seiten
ACT4455 Datasheet, Funktion
ACT4455
Rev 2, 21-Nov-12
36V/5A Step Down DC/DC Converter
FEATURES
7.5V to 36V Input Voltage
40V Input Voltage Surge
Up to 5A Output Current
Up to 12V Output Voltage
Dual Outputs with Independent Over Current
Protection
7.5% Accurate Over Current Protection (OCP)
Integrated 45mHigh Side Power FET
90% Efficiency at Heavy Load
Internal 3ms Soft Startup
Low Standby Input Current
Sleeping Mode at OCP, OTP and SCP
Zero Input and Output Currents at Over Current
and Short Circuit Protection
Auto Recovery into Full Load after Faults
Output Cord Voltage Drop Compensation
Stable with Low ESR Ceramic Output Capacitors
Internal Cycle-by-Cycle Current Control
Programmable Over Current Setting
SOP-8EP Package
APPLICATIONS
Automotive Industry
Dual-Output Car Charger
LCD-TV
GENERAL DESCRIPTION
ACT4455 is a wide input voltage step-down DC/DC
converter with high-side MOSFET integrated. It
provides up to 5A continuous output current at
200kHz switching frequency. The converter can be
configured as single output or dual outputs with
independent over current protection. The converter
achieves high efficiency and excellent load and line
regulation. The converter enters into hiccup and
sleeping mode and the converter power
consumption is nearly zero when output is
overloaded or shorted to ground. Other protection
features includes cycle-by-cycle current limit, under
voltage protection and thermal shutdown. The
device is available in SOP8-EP package.
100
90
80
70
60
50
0
Efficiency vs. Load current
VIN = 12V
VIN = 32V
VIN = 24V
1000
2000
3000
4000 5000
Efficiency (%)
Innovative PowerTM
- 1 - www.active-semi.com
Copyright © 2012 Active-Semi, Inc.






ACT4455 Datasheet, Funktion
ACT4455
Rev 2, 21-Nov-12
APPLICATIONS INFORMATION
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 10kand
determine RFB1 from the following equation:
R FB 1
=
R
FB
2
⎜⎛
0
V OUT
.808
V
1 ⎟⎞
(1)
Over Current Protection Setting
The output over current threshold is calculated by:
IOCP1 = IOCP 2 = 116 mV / RSENSE
(2)
It is recommended that 1% or 0.5% high-accuracy
current sensing resistor is selected to achieve high-
accuracy over current protection. Two over current
protection thresholds can be different based on
different current sensing resistance.
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
V_
OUT
V f I KIN SW LOADMAX RIPPLE
(3)
where VIN is the input voltage, VOUT is the output
voltage, fSW is the switching frequency, ILOADMAX is
the maximum load 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 load current.
With a selected inductor value the peak-to-peak
inductor current is estimated as:
( )ILPK _PK
=
VOUT
×
VIN
V_
OUT
L ×VIN × fSW
(4)
The peak inductor current is estimated as:
ILPK = ILOADMAX
+
1
2
I LPK
_ PK
(5)
The selected inductor should not saturate at ILPK.
The maximum output current is calculated as:
IOUTMAX
=
I_
LIM
1
2
I
LPK
_ PK
(6)
ILIM is the internal current limit, which is typically
6.5A, as shown in Electrical Characteristics Table.
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
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 the 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.
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 RRIPPLE ESR
+
28
VIN
× fSW 2 LCOUT
(7)
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
Innovative PowerTM
- 6 - www.active-semi.com
Copyright © 2012 Active-Semi, Inc.

6 Page









ACT4455 pdf, datenblatt
ACT4455
Rev 2, 21-Nov-12
TYPICAL PERFORMANCE CHARACTERISTICS CONT’D
(Circuit of Figure 7, RCS1 = RCS2 = 50m, L = 18µH, CIN = 150µF, COUT = 680µF, TA = 25°C, unless otherwise specified.)
Input Current at Output Short Output
1.2
1
0.8
0.6
0.4
0.2
0
5
10 15 20 25
30 35
40
Input Voltage (V)
Vcs vs. Temperature
0.18
0.17
0.16
0.15
VCS1
0.14
VCS2
0.13
-25 0 25 50 75 100 125 150
Temperature (°C)
IVVROIUNOLTOU=RT=D1=1=2A5V1V.5
IISET = 2A
VIN = 12V
Start Up
CH1
CH2
CH1: VOUT, 2V/div
CH2: VIN, 5V/div
TIME: 1ms/div
SW vs. Output Ripples
VIN = 12V
IOUT = 0A
CH1
CH2
CH1: Ripper, 50mV/div
CH2: SW, 10V/div
TIME: 2µs/div
SW vs. Output Ripples
CH1
VIN = 12V
IOUT = 4.2A
CH2
CH1: Ripper, 50mV/div
CH2: SW, 10V/div
TIME: 2µs/div
Innovative PowerTM
Load Step Waveforms
VIN = 12V
IOUT1 = 0.08-2.1A
IOUT2 = 0A
CH1
CH2
- 12 -
CH1: VOUT Ripple, 200mV/div
CH2: IOUT, 2A/div
TIME: 400µs/div
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Copyright © 2012 Active-Semi, Inc.

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