AMC DOC. #: AMC3842B_A
November 2001
Copyright 2001, ADD Microtech Corp. 1 www.addmtek.c om
DESCRIPTION FEATURES
The AMC3842B/43B are fixed frequency current-mode
PWM controllers specially designed for OFF-Line switching
power supply and DC-to-DC converters with a minimum
number of external components. These devices feature a
trimmed oscillator for precise duty cycle control, a
temperature compensated reference, high gain error
amplifier, current sensing comparator, and high current
totem pole output which is suitable for driving MOSFETs.
The under voltage lock-out (U.V.L.O.) is designed to
operated with 200µA typ. start-up current, allowing an
efficient bootstrap supply voltage design. The U.V.L.O.
thresholds for the AMC3842B are 16V (on) and 10V (off)
which are ideal for off-line applications. The corresponding
typical threshold for the AMC3843B are 8.4V (on) and 7.6V
(off). The AMC3842B/43B can operated within 100% duty
cycle.
! Low Start-Up current ( typ. 200µ
µµ
µA)
! Optimized for Off-Line and
DC-to-DC Converters
! Maximum Duty Cycle
! U.V.L.O. with Hysteresis
# Operating Frequency Up to 500KHz
# Internal Trimmed Bandgap Reference
# High Current Totem Pole Output
# Error Amplifier With Low Output
Resistance
# Available in 8-Pin Plastic DIP and
Surface Mount 14-Pin S.O.I.C.
# Identical pin assignment to earlier
UC384X series.
APPLICATIONS PACKAGE PIN OUT
! Off-line flyback or forward
converters.
! DC-to-DC buck or boost
converter.
! Monitor Power Supply
8-Pin Plastic DIP
(Top View)
AVAILABLE OPTIONS
Device Start-UP
Voltage Hysteresis Max. Duty
Cycle
AMC3842B 16V 6V < 100%
AMC3843B 8.4V 0.8V < 100%
14-Pin Plastic S.O.I.C.
Surface Mount
(
To
p
View
)
8-Pin Plastic S.O.I.C.
Surface Mount
(Top View)
ORDER INFORMATION
Plastic DIP-8 Plastic SO-14 Plastic SO-8
TA (OC) M 8-pin D 14-pin DM 8-pin
0 to 70 AMC384XBM AMC384XBD AMC384XBDM
Note: All surface-mount packages are available in Tape & Reel. Append the letter “T” to part number (i.e.
AMC384XBDT, or AMC384XBDMT).
CURRENT MODE PWM CONTROLLER
AMC3842B/43B
COMP
VFB
ISENSE
VREF
GND
OUTPUT
VCC
RT/CT
NC
NC
RT/CT
ISENSE
VFB
VREF
VCC
VC
OUTPUT
GND
PWR
NC
NC
COMP
COMP
VFB
ISENSE
VREF
GND
OUTPUT
VCC
RT/CT
A
AA
ADD MICROTECH CORP.
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 2 www.addmtek.c om
ABSOLUTE MAXIMUM RATINGS (Note 1)
Suppl y vol tage, V CC 35V
Output current, IO ± 1A
Analog inputs, VI -0.3V to 6.3V
Error amp output sink current, ISINK(EA) 10mA
Power dissipation (TA = 25 OC), PD 1W
Maximum junct ure temperature, TJ 150 OC
Storage temperature range -65OC to 150OC
Lead temperature (soldiering, 10 seconds) 260 OC
Note 1: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground.
Currents are positive into, negative out of the specified terminal.
THERMAL DATA
M PACKAGE:
Thermal Resistance-Junction to Ambient, θJA 95 OC/W
D PACKAGE:
Thermal Resistance-Junction to Ambient, θJA 120 OC/W
DM PACKAGE:
Thermal Resistance-Junction to Ambient, θJA 165 OC/W
Junct ion Tempera ture Cal culation: TJ = TA + (PD × θJA).
The θJA numbers are guidelines for the thermal performance of the device/pc-board system.
All of the above assume no ambient airflow.
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 3 www.addmtek.c om
BLOCK DIAGRAM
( ) are 14 P in S.O.I.C. pin number
Note 2 :VCC and PWR VC are internally connected for 8 pin packages.
Note 3 :PW R GND and GND are internally connected for 8 pin packages.
Note 4 :U.V.L.O. is 16V for 3842B and 8.4V for 3843B.
Note 5 :Hysteresis is 6V for 3842B and 0.8V for 3843B.
VREF
Internal
Bias 36V
2R
EN
5V
VREF
U.V.L.O.
V
REF
Good Logic
Error Amp Current
Sense
C
Oscillator
R 1V R
S
PWM
Latch
VFB
CURRENT
SENSE
RT/CT PWR
GND
OUTPUT
PWR
VC
GND
VCC
COMP
T
1
(
1
)
2
(
3
)
3
(
5
)
4
(
7
)
8
(
14
)
5
(
8
)
6
(
10
)
7
(
11
)
5
(
9
)
7
(
12
)
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 4 www.addmtek.c om
RECOMMENDED OPERATING CONDITIONS
Recommended Operating Conditions
Parameter Symbol Min. Typ. Max. Units
Supply Voltage VCC / VC 30 V
VI,RT/CT
Input Voltage VI,ISENSE/VFB 0 5.5 V
Output Voltage VO, Output 0 30 V
Supply Current ICC 25 mA
Average Output Current IO 200 mA
Reference Output Current IO(REF) -20 mA
Ti ming Capacitor CT 1 nF
Oscillator Frequency fOSC 100 500 KHz
Operating Free-air Temperature TA 0 70
OC
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, these specifications apply over the operating ambient temperature for AMC384XB with
0OC ≤ TA ≤70 OC; VCC = 15V(note 6); RT = 10K;CT = 3.3nF. Low duty cycle pulse testing techniques are used which
maintains junction and case temperatures equal to the ambient temperature.
AMC384XB
Parameter Symbol Test Co nd itions Min. Typ. Max. Units
Reference Section
Reference output Voltage VREF T
J = 25 OC, IREF = 1mA 4.9 5.0 5.1 V
Line Regul ation 12V ≤ VCC ≤ 25V,TJ = 25 OC 6 20 mV
Load Regulat ion 1mA ≤ IREF ≤ 20mA 6 25 mV
Short Ciruit Output Current ISC T
J = 25 OC -30 -100 -180 mA
Oscillator Section
Oscillation Frequency f TJ = 25 OC 52 KHz
Freq uency Change with Voltage 12V ≤ VCC ≤ 25V 0.2 1.0 %
Freq uency Change with Te mpe rature
(note 7) TMIN ≤ TA ≤ TMAX 5 %
Peak-to-peak Amplitude At RT/CT VOSC 1.7 V
Current Sense Section
Gain (note 8 & 9) AVOL 2.85 3.00 3.15 V/V
Maximum Input Signal (note 8) VI(MAX) COMP = 5V 0.9 1.0 1.1 V
Power Supply Rejection Ratio (note 8) PSRR 12V ≤ VCC ≤ 25V (note 8) 70 dB
Input Bias Current IBIAS -3.0 -10 µA
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 5 www.addmtek.c om
ELECTRICAL CHARACTERISTICS (Cont inued)
Error Amplifier Section
Input Bias Current IBIAS -0.1 -2 µA
Input Voltage VI(EA) COMP = 2.5V 2.42 2.50 2.58 V
Open Loop Voltage Gain GVO 2V ≤ VO ≤ 4V 65 90 dB
Unity Gain Bandwidth (note 7) UGBW TJ = 25 OC 0.7 1 MHz
Power Supply Rejection Ratio PSRR 12V ≤ VCC ≤ 25V 60 70 dB
Output Sink Current ISINK V
FB = 2.7V, COMP = 1.1V 2 7 mA
Output Source Current ISOURCE V
FB = 2.3V, COMP = 5.0V -0.5 -1.0 mA
High Output Vo ltage VOH VFB = 2.3V, RL = 15KΩ to GND 5 6 V
Low Output Voltage VOL VFB = 2.7V, RL = 15KΩ to VREF 0.7 1.1 V
Output Section ISINK = 20mA 0.1 0.4
Output Low Level VOL ISINK = 200mA 1.4 2.2 V
ISOURCE = 20mA 13 13.5
Outp ut High Leve l VOH ISOURCE = 200mA 12 13.0 V
Rise Time (note 7) tr T
J = 25 OC, CL = 1nF 50 150 ns
Fall Time (note 7) tf T
J = 25 OC, CL = 1nF 50 150 ns
Under-Voltage Lockout Section AMC3842B 14.5 16.0 17.5
Start Threshold VTH(ST) AMC3843B 7.8 8.4 9.0 V
AMC3842B 8.5 10 11.5
Min. Oper ating Vo ltage AMC3843B 7.0 7.6 8.2 V
PWM Section
Maximum Duty Cycle AMC3842B/43B 94 97 100 %
Total Standby Current AMC3842B 0.2 0.35
Startup Current AMC3843B 0.5 1.0 mA
Operating Supply Curre nt ICC V
FB = ISENSE = 0V 14 17 mA
Zener Volt age VZ I
CC = 25mA 30 35 V
note 6: Adjust VCC above the start threshold before setting at 15V
note 7: These parameters, although guaranteed, are not 100% tested in production prior to shipment
note 8: Parameters are measured at trip point of latch with VFB = 2V
note 9: Gain is measured between ISENSE and COMP with the input changing from 0V to 0.8V
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 6 www.addmtek.c om
Application Information
Fig. 1. Current Sense Circuit
Peak cu rrent (IS) is set by: IS(MAX) = 1V/RS
Fig. 3. Oscillator Section
1.72
Fig. 2. Error Amplifier Configuration - the
amplifier can source or sink up to 0.5mA For RT < 5K, f = RTCT
Fig. 4. Open-loop laboratory test fixture: Careful grounding techniques are necessary for high peak
currents associated with capacitive loads. Timing and bypass capacitors should be connected to GND pin
in a single point ground. The transistor and 5K potentiometer are used to sample the oscillator waveform
and ap ply an adjust able ramp to the ISENSE pin
GND
ISENSE
COMP
Error
Am
p
RS
Rf
Cf
R
2R
1V Current
Sense
Comparator
4.7K
1
Error AMP
Ad
us
4.7K
2N2222
100K
5
K
ISENSE
Adjust
COMP
VFB
ISENSE
RT/CT
GND
VREF
VCC
Output
0.1µ
µµ
µF
Output
1K,
1W
VCC
VREF
0.1µ
µµ
µF
GND
CT
RT
2.5V
Zf
Zi
0.5mA
VFB
COMP
Error
Am
p
GND
RT/CT
VREF
CT
RT
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 7 www.addmtek.c om
Application Information (continued)
Fig. 5 . Shutdo w n Techni que s - t here are two ways to shutdo wn the PWM controller: 1) raise the voltage at
ISENSE above 1V or, 2) pull the COMP below a voltage two diodes above ground.
Fig 6. Slop Compensation – To achieve duty cycles over 50% for some applications , the above
slop e compensa tion technique is suggested by resistivel y summing a fraction of the
oscillator ramp with the current sense signal.
ISENSE
Shutdown
VREF
500Ω
ΩΩ
Ω
To Current
Sense Resistor
330Ω
ΩΩ
Ω
1K
Shutdown
COMP
VREF
RT/CT
ISENSE
RT
CT
0.1µ
µµ
µF
C
R2
R1
ISENSE
RSENSE
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 8 www.addmtek.c om
8-Pin Plastic DIP
INCHES MILLIMETERS
MIN TYP MAX MIN TYP MAX
A 0.355 0.365 0.400 9.02 9.27 10.16
B 0.240 0.250 0.280 6.10 6.35 7.11
C - - 0.210 - - 5.33
D - 0.018 - - 0.46 -
F - 0.060 - - 1.52 -
G - 0.100 - - 2.54 -
H 0.050 - 0.090 1.27 - 2.29
J 0.008 - 0.015 0.20 - 0.38
K 0.115 0.130 0.150 2.92 3.30 3.81
L 0.300 BSC. 7.62 BSC.
1
B
5
4
8
C
K
F
H G D
A
L
M
J
M - 7º 15º - 7º 15º
8-Pin Plastic S.O.I.C.
INCHES MILLIMETERS
MIN TYP MAX MIN TYP MAX
A 0.183 - 0.202 4.65 - 5.13
B 0.144 - 0.163 3.66 - 4.14
C 0.068 - 0.074 1.73 - 1.88
D 0.010 - 0.020 0.25 - 0.51
F 0.015 - 0.035 0.38 - 0.89
G 0.050 BSC 1.27 BSC
J 0.007 - 0.010 0.19 - 0.25
K 0.005 - 0.010 0.13 - 0.25
L 0.189 - 0.205 4.80 - 5.21
M - - 8º - - 8º
P 0.228 - 0.244 5.79 - 6.20
SEATING PLAN
A
D
F
P
B
K
C
M
L
J
G
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 9 www.addmtek.c om
14-Pin Plastic S.O.I.C.
INCHES MILLIMETERS
MIN TYP MAX MIN TYP MAX
A 0.336 - 0.344 8.54 - 8.74
B 0.159 - 0.158 3.81 - 4.01
C 0.053 - 0.069 1.35 - 1.75
D 0.014 - 0.018 0.35 - 0.46
F 0.026 - 0.030 0.67 - 0.77
G 0.050 BSC 1.27 BSC
J 0.007 - 0.010 0.19 - 0.25
K 0.004 - 0.010 0.10 - 0.25
L 0.189 - 0.205 4.82 - 5.21
M - - 8º - - 8º
P 0.228 - 0.244 5.79 - 6.20
SEATING PLAN
F
M
L
J
GD
P
B
A
C
K
AM C DOC. #: AMC3842B_A AMC3842B/43B
November 2001 CURRENT MODE PWM C ONTROLLER
Copyright 2001, ADD Microtech Corp. 10 www.addmtek.c om
IMPORTANT NOTICE
ADD Microtech (ADDM) reserves the right to make changes to its products or to discontinue any integrated circuit
product or service without notice, and advises its customers to obtain the latest version of relevant information to
verify, before placing orders, that the information being relied on is current.
A few applications using integrated circuit products may involve potential risks of death, personal injury, or severe
property or environmental damage. ADDM integrated circuit products are not designed, intended, authorized, or
warranted to be suitable for use in life-support applications, devices or systems or other critical applications. Use of
ADDM products in such applications is understood to be fully at the risk of the customer. In order to minimize
risks associated with the customer’s applications, the customer should provide adequate design and operating
safeguards.
ADDM assumes to no liability to customer product design or application support. ADDM warrants the performance
of its products to the specifications applicable at the time of sale.
U.S. Asia Pacific region
ADD Microtech Inc.
492 Altamont Drive
Milpitas, CA 95035
ADD Microtech Corp
3F, 132, Sec. 4, Chung Hsiao E. Rd.,
Taipei, Taiwan
TEL: (408) 9410420 TEL: 2-27760166
FAX: (408) 9410864 FAX: 2-27764208