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Primary Side PWM Controller
Preliminary Specification
Features Description
The AS2208 is a simplified pulse width modulation controller, offering similar functionality as that of the AS3842. Based on the AS2214, the AS2208 provides the additional features of low startup current and overvoltage latching, making it a good solution for adapter applications. The PWM function is controlled by the current sense comparator for normal current mode control. The COMP pin, which serves as an input to the current sense comparator, provides a 1 mA current source which can be tied directly to the control loop optocoupler. The output stage is a high current totem pole output that sees only 85 ns delay from the PWM comparator. The AS2208 requires only 100 A of startup current. The undervoltage lockout (UVLO) thresholds are nominally 14V for turn on and 8 V for turn off. The VREG pin, based on a trimmed bandgap reference, provides a temperature compensated 5 V to loads of up to 50 mA. The oscillator discharge current is trimmed to provide guaranteed duty cycle clamping.
Top view
AS2208
* * * * * * *
Low Startup Current Single-start or auto-restart modes Oscillator trimmed for precision duty cycle clamp Standard temperature range extended to 105C Remote on / off control Self limiting supply Voltage Standard current mode control
Pin Configuration --
PDIP (N)
COMP ISNS RT/CT OV 1 2 3 4
8L SOIC (D)
8 7 6 5 VREG VCC OUT GND
COMP ISNS RT/CT OV
1 2 3 4
8 7 6 5
VREG VCC OUT GND
Ordering Information
Package Temperature Range Order Code
8-Pin Plastic DIP 8-Pin Plastic SOIC
0 to 105 C 0 to 105 C
AS2208N AS2208D
ASTEC Semiconductor
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AS2208
Functional Block Diagram
Primary Side PWM Controller
VCC
5V enable
5V Reg.
V REG
VREG S R
ENBL Q
UVLO
ENBL S Q VREG R
Latch Enable 2V5
OV 3V9 S R 1V7 ISNS VCC 1mA COMP 2R
ENBL Q
Fault Latch
VOV Latch
(FAULT) CM PWM VCC
(PWM) 1V R OUT
RT/CT
OSC
(BLANK)
GND
ASTEC Semiconductor
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Primary Side PWM Controller
Pin Function Description
Pin Number Function Description
AS2208
1
COMP
This is the inverting input to the PWM comparator. A divided and level shifted representation of this voltage is compared to the ISNS input to determine OUT duty cycle. A 1 mA current source is provided as a pull-up for an optocoupler. A voltage proportional to inductor current is connected to this pin. The PWM uses this information to terminate the gate drive of the output. Oscillator frequency and maximum duty cycle are set by connecting a resistor (RT) to VREG and a capacitor (CT) to ground. This pin latches OUT low when pulled above 2.5 V. The latch can be reset by pulling OV above 4 V then back to ground. Circuit common ground. This totem pole output is designed to directly drive a power MOSFET switch capable of sourcing and sinking peak currents up to 1 A. Positive supply voltage for the IC. Output of 5V series regulator.
2 3 4 5 6 7 8
ISNS RT/CT OV GND OUT VCC VREG
Absolute Maximum Ratings
Parameter Symbol Rating Unit
Supply Voltage (ICC < 30 mA) Supply Voltage (Low Impedance Source) Reference Current Output Current Output Voltage Continuous Power Dissipation at 25 C Junction Temperature Storage Temperature Range Lead Temperature, Soldering 10 Seconds
VCC VCC IREF IOUT VOUT PD TJ TSTG TL
Self-Limiting 20 200 1 20 500 150 - 65 to 150 300
V V mA A V mW C C C
Stresses greater than those listed under ABSOLUTE MAXIMUM RATINGS may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability.
Recommended Conditions
Parameter Supply Voltage Oscillator Symbol VCC FOSC Rating 10 - 15 50 - 250 Unit V kHz
Typical Thermal Resistance
Package 8L PDIP 8L SOIC JA 95 C/W 175 C/W JC 50 C/W 45 C/W Typical Derating 10.5 mW/C 5.7 mW/C
ASTEC Semiconductor
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AS2208
Electrical Characteristics
Primary Side PWM Controller
Electrical Characteristics are guaranteed over full junction temperature range (0 to 105 C). Ambient temperature must be derated based on power dissipation and package thermal characteristics. Unless otherwise specified, the conditions of test are VCC = 15 V; BOK = 3 V; OV = 0V; RT = 680 ; CT = 10 nF. To override UVLO, VCC should be raised above 18 V prior to test. Parameter 5 V Regulator Output Voltage Line Regulation Load Regulation Temperature Stability Total Output Variation Long-Term Stability Output Noise Voltage Maximum Source Current Oscillator Initial Accuracy Voltage Stability Temperature Stability Amplitude Upper Trip Point Lower Trip Point Discharge Current Duty cycle Limit Over-Temperature Shutdown Current Sense Comparator Transfer Gain ISNS Level Shift Maximum Input Signal Input Bias Current COMP Source Current COMP Swing High Power Supply Rejection Ratio Propagation Delay to Output AV
ISNS
Symbol
Test Condition
Min
Typ
Max
Unit
VREG PSRR
IREG = 1 mA, TJ= 25 C 9 VCC 18 V 1 IREG 20mA
4.90
5.00 5 5 0.2
5.10 15 15 0.4 5.15
V mV mV mV/C V mV V
TCREG Line, Load,Temperature Over 1,000 hrs at 25C VNOISE IMAX 10 f 100kHz, TJ = 25C VREG = 4.8 V 30 4.85
5 50 120
25
180
mA
FOSC
TJ =25C 9 VCC 18 V
108
120 0.2 5 1.55 2.80 1.25
132 1
kHz % % V V V
TCF VOSC VH VL IDSC
TMIN TJ TMAX VRT/CT peak-to-peak
7.50 RT =680 , CT =10nF, TJ =25C 46
8.70 50 140
9.50 55
mA % C
TOT
-0.2 VISNS 0.8 V VISNS = 0 V VCOMP =+5 V VCOMP =+5 V VCOMP =+5 V
2.85
3.00 1.50
3.15
V/V V
VLS VISNS MAX IBIAS
ISNS
1.00
1.08 -1
1.20 -10
V A mA V dB
ICOMPH VCOMPH PSRR tPB
0.6 5.2
1.0 5.6 70 85 150
9 VCC 18 V
ns
ASTEC Semiconductor
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Primary Side PWM Controller
Electrical Characteristics
(cont'd)
AS2208
Electrical Characteristics are guaranteed over full junction temperature range (0 to 105 C). Ambient temperature must be derated based on power dissipation and package thermal characteristics. Unless otherwise specified, the conditions of test are VCC = 15 V; BOK = 3 V; OV = 0V; RT = 680 ; CT = 10 nF. To override UVLO, VCC should be raised above 18 V prior to test. Parameter Output Output Low Level Output Low Level Output High Level Output High Level Rise Time Fall Time Maximum Duty Cycle Minimum Duty Cycle Over-Voltage Input OV Threshold OV Reset Threshold OV Clear Threshold OV Bias Current Under Voltage Lockout Startup Threshold Minimum Operating Voltage after Turn-on Startup Current Operating Supply Current Supply Voltage Clamp Output Impedance to GND in UVLO State VCC (ON) VCC (OFF) ICC ICC VCC Zener ZOUT ICC = 30 mA VCC = 6 V VCC = 13 V 12.5 7.3 14.0 8.0 105 12 18 22.0 15.8 8.5 150 20 V AV A mA V k VOV VVOVH VVOVL IBIAS OV VREG = 5 V, VOV OV Threshold 2.50 3.80 1.10 -1 2.80 4.00 1.75 -0.2 3.10 4.50 2.20 1 V V V A VOL VOL VOH VOH tR tF DMAX DMIN ISINK = 20 mA ISINK = 150 mA ISOURCE = 20 mA ISOURCE = 150 mA CL = 1 nF CL = 1 nF 94 0 13 12 0.1 1.5 13.5 13 50 50 97 150 150 100 0.4 2.2 V V V V ns ns % % Symbol Test Condition Min Typ Max Unit
ASTEC reserves the right to make changes without further notice to any products described herein to improve reliability, function, or design. ASTEC does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights or the rights of others. ASTEC products are not authorized for use as components in life support devices or systems intended for surgical implant into the body or intended to support or sustain life. Buyer agrees to notify ASTEC of any such intended end use whereupon ASTEC will determine availability and suitability of its products for the intended use. ASTEC and the ASTEC logo are trademarks of ASTEC (BSR) PLC.
ASTEC SEMICONDUCTOR
255 Sinclair Frontage Road * Milpitas, California 95035 * Tel. (408) 263-8300 * FAX (408) 263-8340
ASTEC Semiconductor
81
AS2208
Notes
Primary Side PWM Controller
ASTEC Semiconductor
82

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