ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
June 2005
ASM8P18S44ER / ASM8P18S45ER
rev 0.6
Notice: The information in this document is subject to change without notice.
Alliance Semiconductor
2575 Augustine Drive
Santa Clara, CA
Tel: 408.855.4900
Fax: 408.855.4999
Voltage Mode PWM Controller with EMI Reduction
General Description
ASM8P18xx is a high performance, adjustable frequency,
PWM controller with an integrated spread spectrum
modulator for EMI reduction. It contains all the functions
of a standard PWM controller along with a user
configurable spread spectrum modulation with adjustable
spread. ASM8P18xx allows significant system cost
savings by reducing the number of PCB layers and
shielding that are traditionally required to pass EMI
regulation.
ASM8P18xx is the industry's first general purpose EMI
reduction IC, specifically designed for use in SMPS
systems. ASM8P18xx is compatible to any other 3842
PWM controllers.
ASM8P18xx is capable of driving 1A maximum current
output and it covers a wide supply voltage range from 7V
DC to 30V DC. The PWM frequency is selectable from 40
KHz to 400 KHz.
ASM8P18xx provides under voltage lockout, thermal
shutdown, overload, and undercurrent protection. It is
available in 8-pin MicroSO, P-DIP and SOIC package.
Features
30V maximum operating voltage with CMOS
technology
Adjustable PWM frequencies (40 KHz to 400 KHz)
Maximum Output drive current of 1A.
Wide duty cycle range (0% minimum to 95%
maximum)
Spread spectrum modulation with adjustable spread.
Under voltage lockout with hysteresis.
Low startup current: 275?A maximum
Pin compatible with industry standard 3842 PWM
controller.
Temperature range 40
C to +85
C.
Thermal shutdown, overload and undercurrent
protection.
Frequency skip mode.
Available in 8-pin plastic MicroSO, P-DIP and SOIC
packages.
Applications
Off-line converter
DC-DC converter
Monitor power supply
Computer/DVD/STB power supply
Wireless base station power supply
Telecom power supply
Typical Operating Circuit
V
DD
V
DD
V
IN
FSEL
GND
C
T
V
REF
OUT
COMP
R
C
C
C
R
1
R
2
From SMPS Output
R
S
I
SNS
FB
R
D
R
3
ASM8P18xx
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
June 2005
ASM8P18S44ER / ASM8P18S45ER
rev 0.6
Voltage Mode
PWM Controller with EMI Reduction 2 of 11
Notice: The information in this document is subject to change without notice.
Logic Block Diagram
Pin Diagram
8-Pin MicroSO, P-DIP and SOIC
Pin Description
Pin #
Pin Name
Function
1
COMP
Input of the PWM Comparator and output of the error amplifier
2
FB
Feedback, inverting input of the error amplifier
3
I
SNS
Current sense comparator input
4
FSEL
External capacitor selects PWM frequency
5
GND Ground
6
OUT
SS modulated PWM output
7
V
DD
Supply
voltage
8
V
REF
/
R
D
5V output for ASM8PI8S42 and ASM8PI843 parts. External resistor "
R
D
"
to GND sets the modulation spread for the parts with ER suffix.
I
SNS
GND
PWM
SS MOD
Control
OL + UC
SENSE
UVLO
THERMAL
SHUTDOWN
V
BG
DRIVER
Error
Amp
COMP
FB
OUT
V
REF
V
DD
F
SEL
1
2
3
4
8
7
6
5
ASM8P18S42
COMP
FB
I
SNS
F
SEL
GND
OUT
V
DD
V
REF
ASM8P1843
COMP
1
2
3
4
8
7
6
5
FB
I
SNS
F
SEL
GND
OUT
V
DD
R
D
ASM8P18S42ER
ASM8P18S43ER
ASM8P18S44ER
ASM8P18S45ER
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
June 2005
ASM8P18S44ER / ASM8P18S45ER
rev 0.6
Voltage Mode
PWM Controller with EMI Reduction 3 of 11
Notice: The information in this document is subject to change without notice.
Application Information
Spread Spectrum Deviation
The deviation can be determined by selecting the proper
resistor at V
REF
to GND for the parts with `ER' suffix. (Refer
"R
D
Resistor Vs. % Modulation Depth Plot" for resistor
selection)
PWM Frequency
The PWM frequency can be determined by selecting the
proper capacitance (C
T
) at the FSEL pin.
Start-up Current
ASM8P18xx allows a substantial reduction in the start up
current. Low start up current allows high resistance, lower
wattage start-up resistor, to supply controller start up
power.
Under Voltage Lockout (UVLO)
When the power supply voltage is below the start up
threshold voltage, internal circuitry puts the output into low
impedance state and sets the output to zero.
Thermal Shutdown
The output of ASM8P18xx goes down to zero when the
junction temperature of the device rises above 155C. The
device automatically resumes operation when temperature
drops to 126C. This protects the device from thermal
breakdown.
Overload and under current protection
ASM8P18xx provides Cycle by cycle current limit and pulls
down PWM output to low as soon as I
SNS
pin senses a
peak voltage of 1V, with a delay to output of 125 nS
maximum.
At no load condition when the device senses the peak
voltage level of less than 0.1V at I
SNS
pin for a period of
200mS, the oscillator enters in to cycle skip mode. Normal
condition is restored once I
SNS
increases beyond 0.1V for
more than three cycles. Details of cycle skip for different
options are provided in the Electrical Characteristics table.
Absolute Maximum Ratings
Symbol
Parameter
Min
Max
Units
V
DD
Supply Voltage
30
V
I
DD
Supply Current
TBD*
mA
I
OUT
Maximum Output Current
1
A
I
SNS
Current Sense Inputs and feedback
I
SNS,
FB, COMP
5 V
V
REF
Reference Voltage
6
V
V
OSC
Oscillator Voltage
4
V
V
OUT
Output Voltage
30
V
Operation Junction Temperature
-45
150
C
Storage Temperature
-65
150
C
Lead Soldering Temperature (10 Seconds)
300
C
Static Discharge Voltage MIL-STD-883
2
KV
*Maximum output voltage = 30V
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
June 2005
ASM8P18S44ER / ASM8P18S45ER
rev 0.6
Voltage Mode
PWM Controller with EMI Reduction 4 of 11
Notice: The information in this document is subject to change without notice.
Electrical Characteristics
Unless otherwise noted, V
DD
=15V, Capacitor on F
SEL
= 330pf, I
SENS
= 0.5V. Specifications are over the 40C to +85C ambient temperature range. Typical
values are at 25C.
Parameter
Symbol
Conditions
Min
Typ
Max
Units
REFERENCE SECTION
ASM8P18S42 & ASM8P1843
Output voltage
V
REF
T
A
= +25C, I
OUT
= 1mA
4.90
5.00
5.1
V
Line Regulation
N V
REF
12V < V
DD
< 18V, I
OUT
= 5?A
25
mV
Total Reference variation
Line, Temperature
0.7
%
Temperature Stability
TC
REF
0.5
mV/C
Load Regulation (ASM8P1843)
ImA < Io < 20mA
25
mV
ERROR AMPLIFIER SECTION
Input Bias Current
I
BIAS
-20
?A
Input Voltage
V
I
V
pin1
= 1.25V
1.2
1.25
1.3
V
Open Loop Voltage Gain
A
VOL
65
dB
Power Supply Rejection Ratio
PSRR
V
START
< V
CC
< V
CC
max
80
dB
Output Sink Current
I
OL
V
FB
= 1.32V, V
COMP
= 0.15V
-1.5
mA
Output Source Current
I
OH
V
FB
= 1.18V, V
COMP
= 4.17V
0.3
mA
High Output Voltage
V
OH
V
FB
= 1.25V, R
L
= 15KP
4.17
V
Low Output Voltage
V
OL
V
FB
= 1.25V
0.15
V
CURRENT SENSE SECTION
Over Current Protection
Threshold
V
I(MAX)
FB = 0V (V
COMP
= 5V)
0.90
1.00
1.10
V
Delay to output
T
PD
V
FB
= 0V, I
SNS
= 0 to 2V
125
ns
Under Current Sense Period
T
UCS
200
ms
Under Current Recovery Period
T
UCSD
3
Cycles of PWM
Frequency
ASM8P18S42,
ASM8P18S42ER
1/4
ASM8P1843
ASM8P18S43ER
ASM8P18S44ER
1/10
Cycle Skip
Cycle Skip
condition:
I
SENS
R
0.1V
ASM8P18S45ER
No
Skip
x f
S
OUTPUT SECTION
Low Output Voltage
V
OL
I
SINK
= 50mA
I
SINK
= 200mA
0.128
0.470
V
High Output Voltage
V
OH
I
SOURCE
= 50mA
I
SOURCE
= 200mA
At V
DD
=15V
14.71
13.77
V
On Resistance, High
R
DS(ON)H
I
SOURCE
= 0.2A
6.5
P
On Resistance, Low
R
DS(ON)L
I
SINK
= 0.2A
2.5
P
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
June 2005
ASM8P18S44ER / ASM8P18S45ER
rev 0.6
Voltage Mode
PWM Controller with EMI Reduction 5 of 11
Notice: The information in this document is subject to change without notice.
Parameter
Symbol
Conditions
Min
Typ
Max
Units
Rise Time
t
R
T
A
= 25C, C
L
=1nF 30
nS
Fall Time
t
F
T
A
= 25C, C
L
=1nF 30
nS
Shoot Through Current
0
UVLO SECTION
ASM8P1843,
ASM8P18S43ER,
ASM8P18S45ER,
7.8
Start threshold
V
th(START)
ASM8P18S42,
ASM8P18S42ER
ASM8P18S44ER
15.4
V
ASM8P1843,
ASM8P18S43ER,
ASM8P18S45ER
6.7
V
Stop Threshold
V
th(STOP)
ASM8P18S42,
ASM8P18S42ER,
ASM8P18S44ER
10.2
PWM SECTION
PWM frequency
f
S
40 400
kHz
ASM8P18S44ER,
ASM8P18S45ER
0
50
Duty Cycle Range
ASM8P18S42,
ASM8P18S42ER,
ASM8P1843,
ASM8P18S43ER
0
95
%
TOTAL DEVICE
Start up Current
I
ST
275
?A
Peak Output Current
I
OUT(PK)
1000
mA
Operating Current
I
CC(OPR)
V
FB
= 0; I
SNS
= 0.5;
V
DD
= 15V
5 6
mA
Thermal Shutdown
V
Z
Junction Temp
155
C
Thermal Recovery
126
C
SPREAD SPECTRUM SECTION
ASM8P18S43ER,
ASM8P18S45ER
1/20
Modulation Rate
ASM8P18S42,
ASM8P18S42ER,
ASM8P18S44ER
1/10
of Switching
Frequency
(KHz)
Modulation Depth
Refer R
D
Resistor Vs. % Modulation Depth Plot
OSCILLATOR SECTION
Frequency change with Voltage
Df/d V
CC
0.04 0.05
%
Oscillator Amplitude
1.66
V (Pk-Pk)
Temperature Stability
T
OSC
0.1
%/
C
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