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AS2208
Primary Side PWM Controller
Preliminary Specification
Features
Low Startup Current
•
Single-start or auto-restart
•
modes
Oscillator trimmed for precision
•
duty cycle clamp
Standard temperature range
•
extended to 105°C
Remote on / off control
•
Self limiting supply Voltage
•
Standard current mode control
•
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 µA 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.
Pin Configuration
COMP
RT/CT OUT
OV
—
PDIP (N)
Top view
VREG
81
72
VCC ISNS
63
54
GND
8L SOIC (D)
COMP
RT/CT OUT
OV
81
72
63
54
VREG
VCC ISNS
GND
Ordering Information
Package Temperature Range Order Code
8-Pin Plastic DIP 0 to 105° C AS2208N
8-Pin Plastic SOIC 0 to 105° C AS2208D
ASTEC Semiconductor
77
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AS2208
Functional Block Diagram
Primary Side PWM Controller
V
CC
OV
ISNS
2V5
3V9
1V7
V
CC
1mA
V
REG
ENBL
SQ
R
Latch Enable
V
ENBL
SQ
R
VOV Latch
REG
5V enable
SQ
R
Fault Latch
UVLO
ENBL
5V Reg.
V
REG
COMP
RT/CT
ASTEC Semiconductor
1V
2R
R
OSC
CM PWM
78
(FAULT)
(BLANK)
(PWM)
V
CC
OUT
GND
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Primary Side PWM Controller
AS2208
Pin Function Description
Pin Number Function Description
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.
2 ISNS A voltage proportional to inductor current is connected to this pin. The PWM uses this
information to terminate the gate drive of the output.
3 RT/CT Oscillator frequency and maximum duty cycle are set by connecting a resistor (R
T
) to
VREG and a capacitor (CT) to ground.
4 OV 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.
5 GND Circuit common ground.
6 OUT This totem pole output is designed to directly drive a power MOSFET switch capable of
sourcing and sinking peak currents up to 1 A.
7VCCPositive supply voltage for the IC.
8V
REG
Output of 5V series regulator.
Absolute Maximum Ratings
Parameter Symbol Rating Unit
Supply Voltage (ICC < 30 mA) V
Supply Voltage (Low Impedance Source) V
Reference Current I
Output Current I
Output Voltage V
Continuous Power Dissipation at 25° CP
Junction Temperature T
Storage Temperature Range T
Lead Temperature, Soldering 10 Seconds T
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.
CC
CC
REF
OUT
OUT
D
J
STG
L
Self-Limiting V
20 V
200 mA
1A
20 V
500 mW
150 °C
–65 to 150 °C
300 °C
Recommended Conditions
Parameter Symbol Rating Unit
Supply Voltage V
Oscillator F
ASTEC Semiconductor
CC
OSC
10 - 15 V
50 - 250 kHz
Typical Thermal Resistance
Package θJA θJC Typical Derating
8L PDIP 95° C/W 50° C/W 10.5 mW/°C
8L SOIC 175° C/W 45° C/W 5.7 mW/°C
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AS2208
Primary Side PWM Controller
Electrical Characteristics
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 V
BOK = 3 V; OV = 0V; RT = 680 Ω; CT = 10 nF. To override UVLO, V
should be raised above 18 V prior to test.
CC
Parameter Symbol Test Condition Min Typ Max Unit
5 V Regulator
Output Voltage V
REG
Line Regulation PSRR 9 ≤ V
Load Regulation 1≤ I
Temperature Stability TC
REG
I
= 1 mA, TJ= 25° C 4.90 5.00 5.10 V
REG
≤ 18 V 5 15 mV
CC
≤ 20mA 5 15 mV
REG
0.2 0.4 mV/°C
Total Output Variation Line, Load,Temperature 4.85 5.15 V
Long-Term Stability Over 1,000 hrs at 25°C525mV
Output Noise Voltage V
Maximum Source Current I
NOISE
MAX
10 ≤ f ≤ 100kHz, TJ = 25°C50µV
V
= 4.8 V 30 120 180 mA
REG
Oscillator
Initial Accuracy F
OSC
Voltage Stability 9 ≤ V
Temperature Stability TC
Amplitude V
OSC
Upper Trip Point V
Lower Trip Point V
Discharge Current I
DSC
TJ =25°C 108 120 132 kHz
≤ 18 V 0.2 1 %
CC
T
F
H
L
≤ TJ ≤ T
MIN
V
RT/CT
MAX
peak-to-peak 1.55 V
5%
2.80 V
1.25 V
7.50 8.70 9.50 mA
Duty cycle Limit RT =680 Ω, CT =10nF, TJ =25°C465055%
Over-Temperature Shutdown T
OT
140 °C
Current Sense Comparator
Transfer Gain AV
ISNS Level Shift V
Maximum Input Signal V
Input Bias Current I
COMP Source Current I
COMP Swing High V
ISNS MAXVCOMP
BIAS ISNSVCOMP
COMPH
COMPH
Power Supply Rejection Ratio PSRR 9 ≤ V
Propagation Delay to Output t
PB
ISNS
LS
-0.2 ≤ V
V
ISNS
≤ 0.8 V 2.85 3.00 3.15 V/V
ISNS
= 0 V 1.50 V
=+5 V 1.00 1.08 1.20 V
=+5 V -1 -10 µA
V
=+5 V 0.6 1.0 mA
COMP
5.2 5.6 V
≤ 18 V 70 dB
CC
85 150 ns
= 15 V;
CC
ASTEC Semiconductor
80
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Primary Side PWM Controller
AS2208
Electrical Characteristics (cont’d)
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 V
BOK = 3 V; OV = 0V; RT = 680 Ω; CT = 10 nF. To override UVLO, V
should be raised above 18 V prior to test.
CC
Parameter Symbol Test Condition Min Typ Max Unit
Output
Output Low Level V
Output Low Level V
Output High Level V
Output High Level V
Rise Time t
Fall Time t
Maximum Duty Cycle D
Minimum Duty Cycle D
OH
OH
MAX
MIN
I
OL
OL
R
F
= 20 mA 0.1 0.4 V
SINK
I
= 150 mA 1.5 2.2 V
SINK
I
= 20 mA 13 13.5 V
SOURCE
I
= 150 mA 12 13 V
SOURCE
CL = 1 nF 50 150 ns
CL = 1 nF 50 150 ns
94 97 100 %
0 %
Over-Voltage Input
OV Threshold V
OV Reset Threshold V
OV Clear Threshold V
OV Bias Current I
BIAS OVVREG
OV
VOVH
VOVL
= 5 V, V
≤ OV Threshold -1 -0.2 1 µA
OV
2.50 2.80 3.10 V
3.80 4.00 4.50 V
1.10 1.75 2.20 V
Under Voltage Lockout
Startup Threshold V
Minimum Operating Voltage V
(ON) 12.5 14.0 15.8 V
CC
(OFF) 7.3 8.0 8.5 AV
CC
after Turn-on
Startup Current I
Operating Supply Current I
Supply Voltage Clamp V
CC
Output Impedance to GND in Z
CC
CC
Zener ICC = 30 mA 18 V
OUT
VCC = 13 V 105 150 µA
12 20 mA
VCC = 6 V 22.0 kΩ
UVLO State
= 15 V;
CC
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
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AS2208
Notes
Primary Side PWM Controller
ASTEC Semiconductor
82
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