ETC AS2208

AS2208
Primary Side PWM Controller
Preliminary Specification
Features
Description
•
•
Low Startup Current
•
Oscillator trimmed for precision
duty cycle clamp
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.
•
Standard temperature range
extended to 105°C
•
•
•
Remote on / off control
Single-start or auto-restart
modes
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.
Self limiting supply Voltage
Standard current mode control
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 —
Top view
8L SOIC (D)
PDIP (N)
COMP
1
8
VREG
ISNS
2
7
RT/CT
3
OV
4
COMP
1
8
VREG
VCC
ISNS
2
7
VCC
6
OUT
RT/CT
3
6
OUT
5
GND
OV
4
5
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
Primary Side PWM Controller
AS2208
Functional Block Diagram
VCC
5V enable
VREG
ENBL
S
5V Reg.
V REG
UVLO
Q
R
ENBL
Latch Enable
S
Q
VREG
2V5
R
Fault Latch
ENBL
OV
3V9
S
Q
R
VOV Latch
1V7
ISNS
VCC
1mA
COMP
(FAULT)
2R
CM PWM
VCC
(PWM)
1V
RT/CT
OUT
R
(BLANK)
OSC
ASTEC Semiconductor
78
GND
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 (RT) 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.
7
VCC
Positive supply voltage for the IC.
8
VREG
Output of 5V series regulator.
Absolute Maximum Ratings
Parameter
Symbol
Rating
Unit
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
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
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
Typical Thermal Resistance
Parameter
Symbol
Rating
Unit
Package
θJA
θJC
Typical Derating
Supply Voltage
VCC
10 - 15
V
8L PDIP
95° C/W
50° C/W
10.5 mW/°C
Oscillator
FOSC
50 - 250
kHz
8L SOIC
175° C/W
45° C/W
5.7 mW/°C
ASTEC Semiconductor
79
Primary Side PWM Controller
AS2208
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 VCC = 15 V;
BOK = 3 V; OV = 0V; RT = 680 Ω; CT = 10 nF. To override UVLO, VCC should be raised above 18 V prior to test.
Parameter
Symbol
Test Condition
Min
Typ
Max
Unit
4.90
5.00
5.10
V
5 V Regulator
Output Voltage
VREG
IREG = 1 mA, TJ= 25° C
Line Regulation
PSRR
9 ≤ VCC ≤ 18 V
5
15
mV
1≤ IREG ≤ 20mA
5
15
mV
0.2
0.4
mV/°C
5.15
V
25
mV
Load Regulation
Temperature Stability
TCREG
Total Output Variation
Line, Load,Temperature
Long-Term Stability
Over 1,000 hrs at 25°C
5
10 ≤ f ≤ 100kHz, TJ = 25°C
50
Output Noise Voltage
Maximum Source Current
VNOISE
4.85
µV
IMAX
VREG = 4.8 V
30
120
180
mA
FOSC
TJ =25°C
108
Oscillator
Initial Accuracy
Voltage Stability
120
132
kHz
9 ≤ VCC ≤ 18 V
0.2
1
%
5
%
1.55
V
Temperature Stability
TCF
TMIN ≤ TJ ≤ TMAX
Amplitude
VOSC
VRT/CT peak-to-peak
Upper Trip Point
VH
2.80
V
Lower Trip Point
VL
1.25
V
Discharge Current
IDSC
RT =680 Ω, CT =10nF, TJ =25°C
Duty cycle Limit
Over-Temperature Shutdown
7.50
8.70
9.50
mA
46
50
55
%
TOT
°C
140
Current Sense Comparator
Transfer Gain
ISNS Level Shift
AV
ISNS
VLS
-0.2 ≤ VISNS ≤ 0.8 V
VISNS = 0 V
Maximum Input Signal
VISNS MAX
VCOMP =+5 V
Input Bias Current
IBIAS
VCOMP =+5 V
ISNS
COMP Source Current
ICOMPH
COMP Swing High
VCOMPH
Power Supply Rejection Ratio
PSRR
Propagation Delay to Output
tPB
2.85
3.00
3.15
1.50
1.00
VCOMP =+5 V
9 ≤ VCC ≤ 18 V
80
V
1.08
1.20
V
-1
-10
µA
0.6
1.0
mA
5.2
5.6
V
70
dB
85
ASTEC Semiconductor
V/V
150
ns
Primary Side PWM Controller
Electrical Characteristics
AS2208
(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 VCC = 15 V;
BOK = 3 V; OV = 0V; RT = 680 Ω; CT = 10 nF. To override UVLO, VCC should be raised above 18 V prior to test.
Parameter
Symbol
Test Condition
Min
Typ
Max
Unit
Output
Output Low Level
VOL
ISINK = 20 mA
0.1
0.4
V
Output Low Level
VOL
ISINK = 150 mA
1.5
2.2
V
Output High Level
VOH
ISOURCE = 20 mA
13
13.5
V
Output High Level
VOH
ISOURCE = 150 mA
12
13
V
Rise Time
tR
CL = 1 nF
50
150
ns
Fall Time
tF
CL = 1 nF
50
150
ns
97
100
%
Maximum Duty Cycle
DMAX
94
Minimum Duty Cycle
DMIN
0
VOV
2.50
2.80
3.10
V
OV Reset Threshold
VVOVH
3.80
4.00
4.50
V
OV Clear Threshold
VVOVL
1.10
1.75
2.20
V
OV Bias Current
IBIAS OV
-1
-0.2
1
µA
%
Over-Voltage Input
OV Threshold
VREG = 5 V, VOV ≤ OV Threshold
Under Voltage Lockout
Startup Threshold
VCC (ON)
12.5
14.0
15.8
V
Minimum Operating Voltage
after Turn-on
VCC (OFF)
7.3
8.0
8.5
AV
105
150
µA
12
20
mA
Startup Current
Operating Supply Current
Supply Voltage Clamp
Output Impedance to GND in
UVLO State
ICC
VCC = 13 V
ICC
VCC Zener
ZOUT
ICC = 30 mA
VCC = 6 V
18
V
22.0
kΩ
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
Primary Side PWM Controller
AS2208
Notes
ASTEC Semiconductor
82