June 2005
rev 0.6
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
ASM8P18S44ER / ASM8P18S45ER
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
protection.
Frequency skip mode.
Available in 8-pin plastic MicroSO, P-DIP and SOIC
packages.
shutdown,
overload
and
undercurrent
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
FSEL
C
T
GND
ASM8P18xx
V
REF
R
D
COMP
FB
OUT
I
SNS
R
1
R
C
C
C
R
2
R
3
R
S
V
IN
From SMPS Output
Alliance Semiconductor
2575 Augustine Drive
•
Santa Clara, CA
•
Tel: 408.855.4900
•
Fax: 408.855.4999
•
Notice: The information in this document is subject to change without notice.
June 2005
rev 0.6
Logic Block Diagram
V
DD
V
REF
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
ASM8P18S44ER / ASM8P18S45ER
I
SNS
F
SEL
OL + UC
SENSE
PWM
SS MOD
Control
DRIVER
OUT
UVLO
V
BG
THERMAL
SHUTDOWN
Error
Amp
FB
GND
COMP
Pin Diagram
8-Pin MicroSO, P-DIP and SOIC
COMP
FB
I
SNS
F
SEL
1
2
3
4
8
V
REF
V
DD
OUT
GND
COMP
FB
I
SNS
F
SEL
1
2
8
R
D
V
DD
OUT
GND
ASM8P18S42
ASM8P1843
7
6
5
ASM8P18S42ER
7
ASM8P18S43ER
3
ASM8P18S44ER
6
ASM8P18S45ER
4
5
Pin Description
Pin #
1
2
3
4
5
6
7
8
Pin Name
COMP
FB
I
SNS
FSEL
GND
OUT
V
DD
V
REF
/
R
D
Function
Input of the PWM Comparator and output of the error amplifier
Feedback, inverting input of the error amplifier
Current sense comparator input
External capacitor selects PWM frequency
Ground
SS modulated PWM output
Supply voltage
5V output for ASM8PI8S42 and ASM8PI843 parts. External resistor ”
R
D
”
to GND sets the modulation spread for the parts with ER suffix.
Voltage Mode PWM Controller with EMI Reduction
Notice: The information in this document is subject to change without notice.
2 of 11
June 2005
rev 0.6
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.
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
ASM8P18S44ER / ASM8P18S45ER
Thermal Shutdown
The output of ASM8P18xx goes down to zero when the
junction temperature of the device rises above 155°C. The
device automatically resumes operation when temperature
drops to 126°C. 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
V
DD
I
DD
I
OUT
I
SNS
V
REF
V
OSC
V
OUT
Supply Voltage
Supply Current
Maximum Output Current
Current Sense Inputs and feedback
I
SNS,
FB, COMP
Reference Voltage
Oscillator Voltage
Output Voltage
Operation Junction Temperature
Storage Temperature
Lead Soldering Temperature (10 Seconds)
Static Discharge Voltage MIL-STD-883
*Maximum output voltage = 30V
Parameter
Min
Max
30
TBD*
1
5
6
4
30
Units
V
mA
A
V
V
V
V
°C
°C
°C
KV
-45
-65
150
150
300
2
Voltage Mode PWM Controller with EMI Reduction
Notice: The information in this document is subject to change without notice.
3 of 11
June 2005
rev 0.6
Electrical Characteristics
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
ASM8P18S44ER / ASM8P18S45ER
Unless otherwise noted, V
DD
=15V, Capacitor on F
SEL
= 330pf, I
SENS
= 0.5V. Specifications are over the –40°C to +85°C ambient temperature range. Typical
values are at 25°C.
Parameter
REFERENCE SECTION
ASM8P18S42 & ASM8P1843
Output voltage
Line Regulation
Total Reference variation
Temperature Stability
Load Regulation (ASM8P1843)
ERROR AMPLIFIER SECTION
Input Bias Current
Input Voltage
Open Loop Voltage Gain
Power Supply Rejection Ratio
Output Sink Current
Output Source Current
High Output Voltage
Low Output Voltage
CURRENT SENSE SECTION
Over Current Protection
Threshold
Delay to output
Under Current Sense Period
Under Current Recovery Period
Symbol
Conditions
Min
Typ
Max
Units
V
REF
N
V
REF
T
A
= +25°C, I
OUT
= 1mA
12V < V
DD
< 18V, I
OUT
= 5?A
Line, Temperature
4.90
5.00
25
5.1
V
mV
0.7
0.5
%
mV/°C
mV
TC
REF
ImA < Io < 20mA
25
I
BIAS
V
I
A
VOL
PSRR
I
OL
I
OH
V
OH
V
OL
V
START
< V
CC
< V
CC
max
V
FB
= 1.32V, V
COMP
= 0.15V
V
FB
= 1.18V, V
COMP
= 4.17V
V
FB
= 1.25V, R
L
= 15KP
V
FB
= 1.25V
4.17
V
pin1
= 1.25V
1.2
-20
1.25
65
80
-1.5
0.3
1.3
?A
V
dB
dB
mA
mA
V
0.15
V
V
I(MAX)
T
PD
T
UCS
T
UCSD
Cycle Skip
condition:
I
SENS
R
0.1V
FB = 0V (V
COMP
= 5V)
V
FB
= 0V, I
SNS
= 0 to 2V
0.90
1.00
1.10
125
V
ns
ms
Cycles of PWM
Frequency
200
3
ASM8P18S42,
ASM8P18S42ER
ASM8P1843
ASM8P18S43ER
ASM8P18S44ER
ASM8P18S45ER
1/4
1/10
No
Skip
0.128
0.470
14.71
13.77
6.5
2.5
Cycle Skip
x f
S
OUTPUT SECTION
Low Output Voltage
High Output Voltage
On Resistance, High
On Resistance, Low
V
OL
V
OH
R
DS(ON)H
R
DS(ON)L
I
SINK
= 50mA
I
SINK
= 200mA
I
SOURCE
= 50mA
I
SOURCE
= 200mA
I
SOURCE
= 0.2A
I
SINK
= 0.2A
At V
DD
=15V
V
V
P
P
Voltage Mode PWM Controller with EMI Reduction
Notice: The information in this document is subject to change without notice.
4 of 11
June 2005
rev 0.6
Parameter
Rise Time
Fall Time
Shoot Through Current
UVLO SECTION
ASM8P1843,
ASM8P18S43ER,
ASM8P18S45ER,
ASM8P18S42,
ASM8P18S42ER
ASM8P18S44ER
ASM8P1843,
ASM8P18S43ER,
ASM8P18S45ER
ASM8P18S42,
ASM8P18S42ER,
ASM8P18S44ER
ASM8P18S42 / ASM8P18S42ER
ASM8P1843 / ASM8P18S43ER
ASM8P18S44ER / ASM8P18S45ER
Symbol
t
R
t
F
Conditions
T
A
= 25°C, C
L
=1nF
T
A
= 25°C, C
L
=1nF
Min
30
30
Typ
Max
Units
nS
nS
0
7.8
V
15.4
6.7
10.2
V
Start threshold
V
th(START)
Stop Threshold
V
th(STOP)
PWM SECTION
PWM frequency
f
S
ASM8P18S44ER,
ASM8P18S45ER
Duty Cycle Range
ASM8P18S42,
ASM8P18S42ER,
ASM8P1843,
ASM8P18S43ER
I
ST
I
OUT(PK)
I
CC(OPR)
V
Z
V
FB
= 0; I
SNS
= 0.5;
V
DD
= 15V
Junction Temp
1000
5
155
126
ASM8P18S43ER,
ASM8P18S45ER
ASM8P18S42,
ASM8P18S42ER,
ASM8P18S44ER
6
40
0
400
50
%
0
95
kHz
TOTAL DEVICE
Start up Current
Peak Output Current
Operating Current
Thermal Shutdown
Thermal Recovery
SPREAD SPECTRUM SECTION
1/20
1/10
of Switching
Frequency
(KHz)
275
?A
mA
mA
°C
°C
Modulation Rate
Modulation Depth
OSCILLATOR SECTION
Frequency change with Voltage
Oscillator Amplitude
Temperature Stability
T
OSC
Df/d V
CC
Refer R
D
Resistor Vs. % Modulation Depth Plot
0.04
0.05
1.66
%
V (Pk-Pk)
%/°C
0.1
Voltage Mode PWM Controller with EMI Reduction
Notice: The information in this document is subject to change without notice.
5 of 11
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