December 2005
rev 1.2
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 pin compatible to 384x family of
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 (25V
MAX
for Micro SO). The PWM
frequency is selectable from 40 KHz to 400 KHz.
ASM8P18xx provides under voltage lockout, thermal
shutdown, and overload and cycle-by-cycle current limit.
AS8P18S4xx provides cycle slip feature which reduces
no load power consumption of converters. It is available
in 8-pin MicroSO, P-DIP and SOIC Package.
ASM8P18S42ER
ASM8P18S43ER
ASM8P18S45ER
Features
30V
maximum
operating
voltage
with
BiCMOS
technology (25V
MAX
for Micro SO)
Adjustable PWM frequencies
40KHz to 400KHz Operation
Maximum Output drive current of 1A
Wide duty cycle range
(0% minimum to 99% maximum)
Spread Spectrum Modulation with adjustable spread
for EMI Reduction
Under voltage lockout with hysteresis
Low startup current: 700µA maximum
Pin compatible with industry standard 3842 PWM
controller
Temperature range –40°C to +85°C
Thermal shutdown and overload protection
Frequency skip mode at Light load condition
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
IN
FSEL
C
T
GND
ASM8P18xx
V
REF
R
D
COMP
FB
C
C
OUT
I
SNS
R
1
R
2
R
3
R
S
V
DD
R
C
From SMPS Output
Alliance Semiconductor
2575 Augustine Drive
•
Santa Clara, CA
•
Tel: 408.855.4900
•
Fax: 408.855.4999
•
www.alsc.com
Notice: The information in this document is subject to change without notice.
December 2005
rev 1.2
Logic Block Diagram
V
DD
R
SS
ASM8P18S42ER
ASM8P18S43ER
ASM8P18S45ER
I
SNS
OL + UC
SENSE
PWM
SS MOD
Control
DRIVER
OUT
F
SEL
UVLO
V
BG
THERMAL
SHUTDOWN
Error Amp
FB
GND
COMP
Pin Diagram
COMP
FB
I
SNS
F
SEL
1
2
3
4
ASM8P18S42ER
ASM8P18S43ER
8
7
6
R
SS
V
DD
OUT
GND
ASM8P18S45ER
5
Pin Description
Pin #
1
2
3
4
5
6
7
8
Pin Name
COMP
FB
I
SNS
FSEL
GND
OUT
V
DD
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
External resistor “
R
SS
”
to GND sets Depth of Modulation.
R
SS
PWM Controller with EMI Reduction
Notice: The information in this document is subject to change without notice.
2 of 11
December 2005
rev 1.2
Application Information
Spread Spectrum Deviation
The deviation can be determined by selecting the proper
resistor at R
SS
to GND (Refer “R
SS
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
ASM8P18S42ER
ASM8P18S43ER
ASM8P18S45ER
The output of ASM8P18xx goes down to zero when the
junction temperature of the device rises above 160°C. The
device automatically resumes operation when temperature
drops to 130°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
OSC
V
OUT
Supply Voltage
Supply Current
Maximum Output Current
Current Sense Inputs and feedback
I
SNS,
FB, COMP
Oscillator Voltage
Output Voltage
Operation Junction Temperature
Storage Temperature
Lead Soldering Temperature (10 Seconds)
ESD Rating
HBM
MM
Note: For MicroSO Devices Maximum V
DDMAX
= 25V & I
DDMAX
=10mA
Parameter
Min
Max
30
15
1
5
4
30
Units
V
mA
A
V
V
V
°C
°C
°C
KV
V
-45
-65
150
150
300
2
200
Package Thermal Resistance
8-Pin Plastic DIP (θ
JA
)
8-Pin MicroSO (θ
JA
)
8-Pin SO (θ
JA
)
125°C/W
250°C/W
170°C/W
PWM Controller with EMI Reduction
Notice: The information in this document is subject to change without notice.
3 of 11
December 2005
rev 1.2
Electrical Characteristics
ASM8P18S42ER
ASM8P18S43ER
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
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
I
BIAS
V
I
A
VOL
PSRR
I
OL
I
OH
V
OH
V
OL
Conditions
Min
Typ
-170
Max
Units
µA
V
pin1
= 2.5V
1.19
1.25
37
1.29
V
dB
dB
mA
mA
V
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
= 15KΩ
V
FB
= 1.25V
3.6
80
-0.06
-0.13
0.35
V
V
I(MAX)
T
PD
T
UCS
T
UCSD
Cycle Skip
condition:
I
SENS
≤
0.1V
FB = 0V (V
COMP
= 5V)
V
FB
= 0V, Tested with
2V,20nS I
SNS
pulse
0.90
1.00
1.10
125
V
ns
ms
Cycles of PWM
Frequency
175
200
3
375
ASM8P18S42ER
ASM8P18S43ER
ASM8P18S45ER
1/4
1/10
No
Skip
0.312
13.4
0.424
13.91
6.5
2.5
20
20
0
0.57
14.37
V
V
Ω
Ω
nS
nS
x f
S
Cycle Skip
OUTPUT SECTION
Low Output Voltage
High Output Voltage
On Resistance, High
On Resistance, Low
Rise Time
Fall Time
Shoot Through Current
UVLO SECTION
Start threshold
V
th(START)
ASM8P18S43ER,
ASM8P18S45ER,
ASM8P18S42ER
Stop Threshold
PWM frequency
V
th(STOP)
f
S
ASM8P18S43ER,
ASM8P18S45ER
ASM8P18S42ER,
5.8
12
5.5
7
40
9.5
16.5
7.9
11.9
400
kHz
V
V
V
OL
V
OH
R
DS(ON)H
R
DS(ON)L
t
R
t
F
I
SINK
= 0.2A
I
SOURCE
= 0.2A
I
SOURCE
= 0.2A
I
SINK
= 0.2A
T
A
= 25°C, C
L
=1nF
T
A
= 25°C, C
L
=1nF
PWM Controller with EMI Reduction
Notice: The information in this document is subject to change without notice.
4 of 11
December 2005
rev 1.2
Parameter
Duty Cycle Range
ASM8P18S42ER
ASM8P18S43ER
ASM8P18S45ER
Symbol
Conditions
ASM8P18S45ER
ASM8P18S42ER,
ASM8P18S43ER
Min
0
0
Typ
40
Max
47
99
Units
%
TOTAL DEVICE
Start up Current
Peak Output Current
Operating Current
Thermal Shutdown
Thermal Recovery
SPREAD SPECTRUM SECTION
Modulation Rate
Modulation Depth
OSCILLATOR SECTION
Initial Accuracy
Frequency change with Voltage
Oscillator Amplitude
Temperature Stability
T
OSC
f
INIT
Df/d V
CC
1.7
T
A
=25°C
47
48
0.04
1.76
0.12
49
0.05
1.8
KHz
%
V (Pk-Pk)
%/°C
ASM8P18S43ER,
ASM8P18S45ER
ASM8P18S42ER,
1/20
1/10
of Switching
Frequency
(KHz)
I
ST
I
OUT(PK)
I
CC(OPR)
V
Z
V
FB
= 0; I
SNS
= 0.5;
V
DD
= 15V
Junction Temp
250
1
5
155
126
6.2
700
µA
A
mA
°C
°C
Refer R
SS
Resistor Vs. % Modulation Depth Plot
PWM Controller with EMI Reduction
Notice: The information in this document is subject to change without notice.
5 of 11
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