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ACT355A
Rev1, 09-Jul-08
ActivePSRTM Primary Switching Regulators FEATURES
* Multiple Patent-Pending Primary Side
Regulation Technology The ACT355A ensures safe operation with complete protection against all fault conditions. Built-in protection circuitry is provided for output shortcircuit, line under-voltage, and over-temperature conditions. The ACT355A ActivePSR is optimized for costsensitive applications, and utilizes Active-semi's proprietary primary-side feedback architecture to provide accurate constant voltage, constant current (CV/CC) regulation without the need of an optocoupler or reference device. Integrated line and primary inductance compensation circuitry provides accurate constant current operation despite wide variations in line voltage and primary inductance. Integrated output cord resistance compensation further enhances output accuracy. These products achieve excellent regulation and transient response, yet requires less than 300mW of standby power. The ACT355A is optimized for 2.5W to 3.5W applications (such as 5V/500mA to 5V/700mA CV/CC chargers). It is available in a tiny SOT23-5 package. Figure 1: Typical Application Circuit
HIGH VOLTAGE DC
* No Opto-coupler * Best Constant Voltage, Constant Current
Over All Accuracy
* Minimum External Components * Integrated Line and Primary Inductance
Compensation
* Integrated Output Cord Resistance Compensation
* Line Under-Voltage Protection * Short Circuit Protection * Over Temperature Protection * Flyback Topology in DCM Operation * Complies with all Global Energy Efficient
Regulations: 0.3W Standby Power and CEC Average Efficiency
* SOT23-5 Package
APPLICATIONS
* Chargers for Cell Phones, PDAs, MP3,
Portable Media Players, DSCs, and Other Portable Devices and Appliances
+
NP NS
CV/CC OUTPUT
* RCC Adapter Replacements * Linear Adapter Replacements * Standby and Auxiliary Supplies
GENERAL DESCRIPTION
The ACT355A belongs to the high performance, multiple patent-pending ActivePSRTM Family of universal-input AC/DC off-line controllers for battery charger and adapter applications. It is designed for the flyback topology working in a discontinuous conduction mode (DCM). In addition to being the industry's most accurate primary side regulator, the ACT355A meets all of the global energy efficiency regulations (CEC, European Blue Angel, and US Energy Star standards) while using very few external components.
+
VDD
SW R5 NA
ACT355A
FB G
R6
Micro Bridge Technology Co.,Ltd.
ACT355A
Rev1, 09-Jul-08
ORDERING INFORMATION
PART NUMBER
ACT355AUC-T
TEMPERATURE RANGE
-40C to 85C
PACKAGE
SOT23-5
PINS
5
PACKING METHOD
TAPE & REEL
TOP MARK
PSRI
PIN CONFIGURATION
FB
1
5
VDD
PSRI
G
2
NC
3
4
SW
SOT23-5 ACT355AUC-T
PIN DESCRIPTIONS
PIN NUMBER
1 2 3 4 5
PIN NAME
FB G NC SW VDD Ground. No Connection.
PIN DESCRIPTION
Feedback Pin. Connect to a resistor divider network from the auxiliary winding.
Switch Driver. Connect this pin to the emitter of the power NPN transistor or source of the power MOSFET. Power Supply.
Micro Bridge Technology Co.,Ltd.
ACT355A
Rev1, 09-Jul-08
ABSOLUTE MAXIMUM RATINGS
PARAMETER
VDD to G Maximum Continuous VDD Current FB to G SW to G Continuous SW Current Maximum Power Dissipation (derate 5.3mW/C above TA = 50C) Junction to Ambient Thermal Resistance (JA) Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 sec)
VALUE
-0.3 to +23.5 20 -0.3 to +6 -0.3 to +23.5 Internally limited 0.53 190 -40 to 150 -55 to 150 300
UNIT
V mA V V A W C/W C C 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
(VDD = 15V, VOUT = 5V, LP = 2mH, NP = 130, NS = 10, NA = 32, TA = 25C, unless otherwise specified.)
PARAMETER
VDD Turn-On Voltage VDD Turn-Off Voltage VDD OVP Trigger Voltage Supply Current Start Up Supply Current Clamp Switching Frequency Effective FB Feedback Voltage Output Cord Resistance Compensation Primary Current Limit Maximum Duty Cycle Switch On-Resistance SW Rise Time SW Fall Time SW Off Leakage Current Over-Temperature Threshold
SYMBOL
VDDON VDDOFF VDDOVP IDD IDDST VFB ILIM DMAX RON
TEST CONDITIONS
VDD Rising VDD Falling
MIN
16.4 7 18.2
TYP
19.4 7.5 20.5 0.8 30
MAX
22.0 8 22.5 1.5 55 58 3.520
UNIT
V V V mA A kHz V % mA
VDD = 15V, before turn-on 45 FB in Regulation Maximum Output Power ISW = 10mA ISW = 50mA 1nF load, 15 pull-up 1nF load, 15 pull-up Switch in off-state, VSW = 22V 80 3.415
3.467 +3.7 320 86 3.5 30 20 1 160
92 5
% ns ns
10
A C
Micro Bridge Technology Co.,Ltd.
ACT355A
Rev1, 09-Jul-08
FUNCTIONAL BLOCK DIAGRAM
SW VDD
REGULATOR & UVLO REFERENCE
FB
3.45V
+
DIFFERENTIAL PREAMP
-
SIGNAL FILTER
+
-
ERROR AMPLIFIER
+
+
-
CURRENT MODE PWM COMPARATOR PFWM CONTROL
DC CORD COMP
CURRENT SHAPING
OSCILLATOR & RAMP
G
FUNCTIONAL DESCRIPTION
As shown in the Functional Block Diagram, the ACT355A feedback regulation is done via several circuit blocks to pre-amplify the FB pin error voltage relative to an internal reference, filter out the switching transients, and integrate the resulting useful differential error voltage for current mode PFWM (Pulse Frequency and Width Modulation) control. SW is a driver output that drives the emitter of an external high voltage NPN transistor or N-channel MOSFET. This emitter-drive method takes advantage of the high VCBO of the transistor, allowing a low cost transistor such as `13003 (VCBO = 700V) or `13002 (VCBO = 600V) to be used for a wide AC input range.
Constant Voltage (CV) Mode
In constant voltage operation, the IC captures the auxiliary flyback signal at FB pin through a resistor divider network R5 and R6 in the simplified application circuit. The FB pin is pre-amplified against the reference voltage, and the secondary side output voltage error is extracted based on Active-Semi's proprietary filter architecture. This error signal is then integrated by the Error Amplifier . When the secondary output voltage is above regulation, the Error Amplifier output voltage decreases to reduce the switch current. When the secondary side is below regulation, the Error Amplifier output voltage increases to ramp up the switch current to bring the secondary output back to regulation. The output regulation voltage is determined by the following relationship:
R 5 N S VOUTCV = 3 .45 V x 1 + R 6 N A - VF
Startup Mode
VDD is the power supply terminal for the IC. During startup, the IC typically draws 30A supply current. The bleed resistor from the rectified high voltage DC rail supplies current to VDD until it exceeds the VDDON threshold of 19.4V. At this point, the IC enters normal operation when switching begins and the output voltage begins to rise. The VDD bypass capacitor must supply the IC and the NPN base drive until the output voltage builds up enough to provide power from the auxiliary winding to sustain the VDD. The VDDOFF threshold is 7.5V, and therefore, the voltage on the VDD capacitor must not drop more than 10V while the output is charging up.
(1)
where R5 and R6 are top and bottom feedback resistor, NS and NA are numbers of transformer secondary and auxiliary turns, and VF is the rectifier diode forward drop voltage at approximately 0.1A bias. The ACT355A includes internal feedback loop compensation to simplify application circuit design.
Micro Bridge Technology Co.,Ltd.
ACT355A
Rev1, 09-Jul-08
Constant Current (CC) Mode
When the secondary output current reaches a level set by the internal current limiting circuit, the IC enters current limit condition and causes the secondary output voltage to drop. As the output voltage decreases, so does the flyback voltage in a proportional manner. An Internal current shaping circuitry adjusts the switching frequency based on the flyback voltage so that the transferred power remains proportional to the output voltage, resulting in a constant secondary side output current profile. The energy transferred to the output during each switching cycle is 1/2(LP x ILIM2) x , where LP is the transformer primary inductance, ILIM is the primary peak current, and is the conversion efficiency. From this formula, the constant output current can be derived:
IOUTCC 1 2 x fSW = LP x ILIM V 2 OUTCV
Loop Compensation
The ACT355A integrates loop compensation circuitry for simplified application design, optimized transient response, and minimal external components.
Primary Inductance Compensation
The ACT355A includes built-in primary inductance compensation to maintain constant current regulation despite variations in transformer manufacturing.
Peak Inductor Current Limit Compensation
The ACT355A includes peak inductor current limit compensation to achieve constant input power over wide line and wide load range.
Output Cord Resistance Compensation
The ACT355A provides automatic output cord resistance compensation during constant voltage regulation, monotonically adding an output voltage correction up to a typical correction of 3.2% at full power. This feature allows for better output voltage accuracy by compensating for the output voltage droop due to the output cord resistance.
(2)
where fSW is the nominal switching frequency and VOUTCV is the nominal secondary output voltage. The constant current operation typically extends down to lower than 40% of output voltage regulation.
Light Load Mode
When the secondary side output load current decreases to an internally set light load level, the IC's switching frequency is also reduced to save power. This enables the application to meet all current green energy standards. The actual minimum switching frequency is programmable with a small dummy load (while still meeting standby power).
Short Circuit Mode
When the secondary side output is short circuited, the ACT355A enters hiccup mode operation. In this condition, the auxiliary supply voltage collapses and the VDD voltage drops below the VDDOFF threshold. This turns off the IC and causes it to restart. This hiccup behavior continues until the short circuit is removed.
Output Over Voltage Protection
The ACT355A includes output over-voltage protection circuitry, which shuts down the IC when the output voltage is 40% above the normal regulation voltage or when no feedback signal is detected for 8 consecutive switching cycles. The IC enters hiccup mode when an output over voltage fault is detected.
Micro Bridge Technology Co.,Ltd.
ACT355A
Rev1, 09-Jul-08
APPLICATIONS INFORMATION
Figure 2: NPN Transistor Reverse Bias Safe Operation Area
IC
is driven at its emitter. Thus, the ACT355A+'13002 or `13003 combination meets the necessary breakdown safety requirement. Table 1 lists the breakdown voltage of some transistors appropriate for use with the ACT355A. The power dissipated in the NPN transistor is equal to the collector current times the collector-emitter voltage. As a result, the transistor must always be in saturation when turned on to prevent excessive power dissipation. Select an NPN transistor with sufficiently high current gain (hFEMIN > 8) and a base drive resistor low enough to ensure that the transistor easily saturates.
Base-Drive Safe Region (RCC)
Emitter-Drive Safe Region
VCEO
VCBO
VC
Table 1: Recommended NPN Transistor DEVICE
MJE13002
External Power Transistor
The ACT355A allows a low-cost high voltage power NPN transistor such as `13003 or `13002 to be used safely in flyback configuration. The required collector voltage rating for VAC = 265V with full output load is at least 600V to 700V. As seen from Figure 2, NPN Reverse Bias Safe Operation Area, the breakdown voltage of an NPN is significantly improved when it
VCBO VCEO
600V
IC
hFEMIN PACKAGE
25 25 25 TO-126 TO-126 TO-92
300V 1.5A 400V 1.5A 400V 1A
MJE13003, 700V KSE13003 STX13003 700V
Figure 3: Typical Application Circuit
R12 L FR1 L1 T1 D4 VIN = 85 to 265VAC D3 N C8 R5 D7 R9 R10 VDD FB SW Q1 D2 + C1 + C2 D1 R7 R8 R4 R2 R3 D6 C3 D8 + C6 VO C5 R11 GND
D5
C1, C2 C3 C4 C5 C6 C7 C8
C7
4.7F/400V 4.7nF/1kV 4.7F/25V 680F/10V 1nF/50V 470pF/50V 680pF/50V 1N4007 FR107 HER103 1N4148 SB240
Q1 L1 FR1 R2, R7, R8 R3, R10 R4 R5 R6 R9 R11 R12 T1
'13002S, TO-92 1.5mH 10 750k 100 33 See Table 2 See Table 2 390 1k 10 See Table 2
ACT355A
G
R6
+
C4
D1-D4 D5 D6 D7 D8
Micro Bridge Technology Co.,Ltd.
ACT355A
Rev1, 09-Jul-08
Design Procedure
Figure 3, Typical Application Circuit, shows a complete, optimized constant voltage/constant current charger application. The application design procedure for using the ACT355A is simple. Three components determine the output constant voltage and constant current settings: the transformer T1 and resistors R5 and R6. Refer to Table 2 for selection values for these three key components for different typical design cases. The Typical Application Circuit in Figure 3 lists component values of other devices in the a complete charger application. Table 2: Component Selection Table OUTPUT VO (V)
5.0 5.0 5.0
Design Notes
1) Feedback resistors R5 and R6 must meet the 1% maximum tolerance to have good V0 regulation. 2) The value of the feedback resistor can be chosen slightly different from the table according to the actual system efficiencies in different systems. 3) C8 must be added to guarantee good CC accuracy.
DESIGN CASE
1 2 3
IO (mA)
500 600 650
ActivePSRTM PART NUMBER
ACT355A ACT355A ACT355A
TRANSFORMER NP
130 130 130
RESISTOR NETWORK LP7% (mH)
1.6 1.8 1.9
NA
32 32 32
NS
10 10 10
R51% (k)
26.7 31.6 34.4
R61% (k)
6.98 8.25 9.09
Micro Bridge Technology Co.,Ltd.
ACT355A
Rev1, 09-Jul-08
PACKAGE OUTLINE
SOT23-5 PACKAGE OUTLINE AND DIMENSIONS
?
b L1
0.2
SYMBOL
A
DIMENSION IN MILLIMETERS MIN
1.050 0.000 1.050 0.300 0.100 2.820 1.500 2.650
DIMENSION IN INCHES MIN
0.041 0.000 0.041 0.012 0.004 0.111 0.059 0.104
MAX
1.250 0.100 1.150 0.500 0.200 3.020 1.700 2.950
MAX
0.049 0.004 0.045 0.020 0.008 0.119 0.067 0.116
D E1 E
A1 A2
L
e e1
c
b c D E
A1
A2
A
E1 e e1 L L1
0.950 TYP 1.800 2.000
0.037 TYP 0.071 0.079
0.700 REF 0.300 0 0.600 8
0.028 REF 0.012 0 0.024 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
Micro Bridge Technology Co.,Ltd.

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