Datenblatt-pdf.com

ACT4070 Schematic ( PDF Datasheet ) - Active-Semi

Teilenummer ACT4070
Beschreibung Wide Input 3A Step Down Converter
Hersteller Active-Semi
Logo Active-Semi Logo 



Gesamt 10 Seiten
		
ACT4070 Datasheet, Funktion
www.DataSheet4U.com
ACT4070
Rev 0, 12/2006
Wide Input 3A Step Down Converter
FEATURES
 3A Output Current
 Up to 95% Efficiency
 4.5V to 30V Input Range
 6µA Shutdown Supply Current
 400kHz Switching Frequency
 Adjustable Output Voltage
 Cycle-by-Cycle Current Limit Protection
 Thermal Shutdown Protection
 Internal Soft Start Function
 Frequency Fold Back at Short Circuit
 Stability with Wide Range of Capacitors,
Including Low ESR Ceramic Capacitors
 SOP-8/EP (Exposed Pad) Package
APPLICATIONS
 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
GENERAL DESCRIPTION
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.
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.
The ACT4070 is available in SOP-8/EP exposed
pad package and requires very few external
devices for operation.
TYPICAL APPLICATION CIRCUIT
Innovative Products. Active Solutions.
-1-
Copyright © 2006 Active-Semi, Inc.
www.active-semi.com






ACT4070 Datasheet, Funktion
www.DataSheet4U.com
ACT4070
Stability compensation
Figure 2:
Stability Compensation
: CCOMP2 is needed only for high ESR output capacitor
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:
AVDC
1.222V
IOUT
AVEAGCOMP
(4)
The dominant pole P1 is due to CCOMP:
fP 1
G EA
2 AVEA C COMP
(5)
The second pole P2 is the output pole:
fP 2
IOUT
2VOUT COUT
(6)
The first zero Z1 is due to RCOMP and CCOMP:
fZ1
1
2RCOMP CCOMP
(7)
And finally, the third pole is due to RCOMP and
CCOMP2 (if CCOMP2 is used):
fP 3
1
2RCOMP CCOMP2
(8)
Follow the following steps to compensate the IC:
STEP 1. Set the cross over frequency at 1/10 of
the switching frequency via RCOMP:
RCOMP
2VOUT COUT fSW
10 GEAGCOMP 1.222 V
1.25 x10 8VOUT COUT
(Ω)
but limit RCOMP to 15kΩ maximum.
(9)
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:
CCOMP
1.6 x10 5
RCOMP
(F) (10)
If RCOMP is limited to 15kΩ, then the actual cross
over frequency is 4.8/(VOUTCOUT). Therefore:
CCOMP
8.8
x10
V6
OUT
COUT
(F) (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 us-
ing CCOMP2 is:
RESROUT
Min
1.1x10
COUT
6
,0.012VOUT

) (12)
And the proper value for CCOMP2 is:
CCOMP
COUT RESROUT
RCOMP
(13)
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.
Table 2 shows some calculated results based on
the compensation method above.
Table 2:
Typical Compensation for Different Output
Voltages and Output Capacitors
VOUT
1.8V
COUT
22μF Ceramic
RCOMP
4kΩ
CCOMP CCOMP2
3.3nF 220pF
2.5V 22μF Ceramic 5.6kΩ 3.3nF 220pF
5V 22μF Ceramic 12kΩ 1.5nF 220pF
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
: CCOMP2 is needed for board parasitic and high ESR output
capacitor.
Figure 3 shows a sample ACT4070 application
circuit generating a 2.5V/3A output.
Innovative Products. Active Solutions.
-6-
Copyright © 2006 Active-Semi, Inc.
www.active-semi.com

6 Page


SeitenGesamt 10 Seiten
PDF Download[ ACT4070.PDF ]

Link teilen




Besondere Datenblatt

TeilenummerBeschreibungHersteller
ACT4070Wide Input 3A Step Down ConverterActive-Semi
Active-Semi
ACT4070Wide Input 3A Step Down ConverterActive-Semi
Active-Semi
ACT4070BWide Input 3A Step Down ConverterActive-Semi
Active-Semi
ACT4072Wide Input 2A Step Down ConverterActive-Semi
Active-Semi
ACT4075Wide Input 2.5A Step Down ConverterActive-Semi
Active-Semi

TeilenummerBeschreibungHersteller
CD40175BC

Hex D-Type Flip-Flop / Quad D-Type Flip-Flop.

Fairchild Semiconductor
Fairchild Semiconductor
KTD1146

EPITAXIAL PLANAR NPN TRANSISTOR.

KEC
KEC


www.Datenblatt-PDF.com    |   2020   |  Kontakt  |   Suche