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19-2830; Rev 0; 4/03
Synchronizable, High-Frequency Current- and
Voltage-Mode PWM Controllers for Isolated Supplies
General Description
The MAX8540/MAX8541 pulse-width-modulated (PWM)
controllers for forward/flyback isolated DC-to-DC convert-
ers provide maximum flexibility to power-supply design-
ers and reduce external component count. These
controllers allow common PC board layout for current-
mode (MAX8540) and voltage-mode (MAX8541) designs.
Both controllers feature adjustable switching frequency
and external synchronization from 200kHz to 1MHz.
Active-high and active-low enable, undervoltage pro-
tection (UVP), and overvoltage protection (OVP) reduce
external component count.
Maximum duty cycle is adjustable, and the feed-forward
function scales the maximum duty cycle with input volt-
age to limit the maximum volt-seconds applied to the
transformer primary. The MAX8540 allows the user to
select the value of slope compensation to further opti-
mize magnetics design. The MAX8541 features user-
adjustable ramp magnitude for the PWM comparator.
A cycle-by-cycle current-limit function controls the peak
primary current during overload and short circuit. Both
controllers can be set to latch off or to hiccup when a
short circuit is detected. The number of current-limited
cycles to initiate the hiccup mode and number of
cycles skipped are user selectable to allow startup with
high-capacitance loads and protect the converter
against sustained short circuits.
The MAX8540/MAX8541 feature 9Ω internal gate dri-
vers for low-power applications and are compatible
with external gate drivers for high-power applications.
Both devices are available in the space-saving 16-pin
QSOP package.
The MAX8541 EV kit evaluates the MAX8540 and the
MAX8541 to speed designs. Design examples are also
available in application notes:
50W Voltage-Mode
Forward Converter Design with the MAX8541
and
50W
Current-Mode Forward Converter Design with the
MAX8540.
♦
Synchronization to External Clock
♦
Programmable, Constant Maximum Volt-Second
Simplifies Transformer Design
♦
Programmable Hiccup/Skip Cycles or Latch-Mode
Protection
♦
Clean Startups with High-Capacitance Loads
♦
Programmable Under/Overvoltage Protection
♦
Current-Mode, Adjustable Slope Compensation
(MAX8540)
♦
Voltage-Mode, Adjustable Ramp Magnitude
(MAX8541)
♦
10mA, 5V Regulator
♦
75mV to 1.25mV Adjustable Current Limit
Reduces External Components
♦
Internal Gate Driver for Low-Power Applications
♦
External Gate Driver for High-Power Applications
Features
♦
200kHz to 1MHz Adjustable Switching Frequency
MAX8540/MAX8541
Ordering Information
PART
MAX8540EEE
MAX8541EEE
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
16 QSOP
Pin Configurations
TOP VIEW
REF 1
OV 2
UV 3
FREQ/SYNC 4
SS 5
MAXDTY 6
EN 7
SCOMP 8
16 V
CC
15 DRV
14 GND
Applications
Isolated DC-to-DC Modules (Bricks)
Cellular Base Stations
Telecom and Network Systems
High-Performance Off-Line AC/DC Converters
MAX8540EEE
13 SKTON
12 CS
11 SKTOFF
10 ILIM
9
OPTO
QSOP
Functional Diagrams and Typical Operating Circuit appear
at end of data sheet.
Pin Configurations continued at end of data sheet.
1
________________________________________________________________
Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Synchronizable, High-Frequency Current- and
Voltage-Mode PWM Controllers for Isolated Supplies
MAX8540/MAX8541
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND ............................................................-0.3V to +20V
OPTO, UV, OV,
EN,
PRAMP, ILIM, REF to GND ......-0.3V to +6V
SCOMP, FREQ, CS, SKTON, SKTOFF, SS,
MAXDTY to GND .....................................-0.3V to V
REF
+ 0.3V
DRV to GND ................................................-0.3V to V
VCC
+ 0.3V
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
VCC
= 12V, C
REF
= 1µF, V
UV
= V
OV
= V
OPTO
, V
ILIM
= 2V, R
FREQ/SYNC
= 32.4kΩ, C
SS
= 0.1µF, R
MAXDTY
= 97.6kΩ, V
EN
= 0,
R
SCOMP
= 68kΩ, R
PRAMP
= 25kΩ, C
SKTON
= 0.01µF, C
SKTOFF
= 0.1µF, V
CS
= 0.6V, C
DRV
= 10pF,
T
A
= 0°C to +85°C,
unless otherwise
noted. Typical values are at T
A
= +25°C.)
PARAMETER
V
CC
Operating Voltage Range
Undervoltage Lockout
Undervoltage Lockout Hysteresis
Supply Current
Shutdown Current
REF
Output Voltage
Load Regulation
Line Regulation
Pulldown Resistor in Shutdown
I
REF
= 0
I
REF
= 0 to 10 mA
V
VCC
= 8.4V to 18V
V
EN
= 3V
V
UV
rising, 120mV typical hysteresis
V
UV
falling
V
OV
rising, 130mV typical hysteresis
V
OV
falling
V
IL
V
IH
V
EN
= 2.6V
2.6
5
0.075
110
±10
1.175
1.250
1.330
17
1.250
150
1.200
1.083
-0.5
2.9
2.778
4.9
5.0
20
5
10
1.250
1.128
+0.01
3.021
2.894
5.1
50
20
30
1.300
1.173
+0.5
3.1
3.010
1.2
V
mV
mV
Ω
V
REF
is active,
I
REF
= 0
V
EN
= 3V
No switching
Switching with no load
(Note 1)
V
CC
rising
V
CC
falling
7.6
7.6
6.6
0.9
8.0
7.0
1.0
3.5
5
0.5
4.2
6.3
0.9
18.0
8.4
7.4
V
V
V
mA
mA
CONDITIONS
MIN
TYP
MAX
UNITS
UNDERVOLTAGE/OVERVOLTAGE (UV/OV)
UVLO Threshold
Input Bias Current
OVLO Threshold
EN
Input Low Threshold
Input High Threshold
Pullup Current
CURRENT LIMIT
V
ILIM
Range
CS Current-Limit to DRV Turn-Off
Includes leading-edge blanking time
Delay
V
CS
Cycle-by-Cycle Threshold
Voltage
Accuracy when V
ILIM
= 0.075V
V
ILIM
= 1.250V
V
ns
%
V
V
V
µA
V
µA
V
2
_______________________________________________________________________________________
Synchronizable, High-Frequency Current- and
Voltage-Mode PWM Controllers for Isolated Supplies
ELECTRICAL CHARACTERISTICS (continued)
(V
VCC
= 12V, C
REF
= 1µF, V
UV
= V
OV
= V
OPTO
, V
ILIM
= 2V, R
FREQ/SYNC
= 32.4kΩ, C
SS
= 0.1µF, R
MAXDTY
= 97.6kΩ, V
EN
= 0,
R
SCOMP
= 68kΩ, R
PRAMP
= 25kΩ, C
SKTON
= 0.01µF, C
SKTOFF
= 0.1µF, V
CS
= 0.6V, C
DRV
= 10pF,
T
A
= 0°C to +85°C,
unless otherwise
noted. Typical values are at T
A
= +25°C.)
PARAMETER
ILIM Leakage Current
Hiccup Skip Off-Time
Hiccup Skip Off-Charging
Hiccup Skip On-Time
Hiccup Skip On-Charging
Current
Hiccup SKTOFF Voltage
Threshold
OPTO
Input Bias Current
Minimum Input Voltage
Maximum Input Voltage
DUTY CYCLE
R
MAXDTY
= 24.3kΩ, V
UV
= 1.3V
R
MAXDTY
= 130kΩ, V
UV
= 1.3V
Maximum Duty Cycle
V
UV
= 1.3V, R
MAXDTY
= 97.6kΩ
Internally programmed limit for maximum duty cycle at
all frequencies
SOFT-START
Source Current
V
SS
= 1V
4.5
5.5
10
440
280
300
200
1000
1.5
0.1
2.5
1
0.5
30
57
V
320
6.5
30
µA
Ω
ms/µF
kHz
kHz
Pulldown Resistance in Shutdown I
SS
= 10mA, V
E N
= 3V
Time
FREQUENCY
Initial Accuracy
Switching Frequency Range
SCOMP (MAX8540)
Slope Compensation
PRAMP (MAX8541)
R
PRAMP
= 12.4kΩ
Ramp Voltage Amplitude
DRV (MOSFET DRIVER)
Rise Time
C
DRV
= 500pF, 10% to 90% of V
VCC
C
DRV
= 2000pF, 10% to 90% of V
VCC
ns
R
PRAMP
= 21kΩ
R
PRAMP
= 42kΩ
R
SCOMP
= 14kΩ
R
SCOMP
= 204kΩ
V
R
FREQ
= 32.4kΩ
R
FREQ
= 48.7kΩ
R
FREQ
= 8.87kΩ
79
15
80
60
80
82
%
V
OPTO
= 3.5V
Minimum voltage for duty-cycle control
Maximum voltage for duty-cycle control
30
0.6
2.6
µA
V
V
C
SKTOFF
= 0.1µF (Note 3)
0.9
C
SKTON
= 0.01µF (Note 3)
1.5
2.3
CONDITIONS
MIN
-1
90
1.5
9
2.5
2.5
3.5
2.7
2.1
TYP
MAX
+1
UNITS
µA
ms
µA
ms
µA
V
MAX8540/MAX8541
_______________________________________________________________________________________
3
Synchronizable, High-Frequency Current- and
Voltage-Mode PWM Controllers for Isolated Supplies
MAX8540/MAX8541
ELECTRICAL CHARACTERISTICS (continued)
(V
VCC
= 12V, C
REF
= 1µF, V
UV
= V
OV
= V
OPTO
, V
ILIM
= 2V, R
FREQ/SYNC
= 32.4kΩ, C
SS
= 0.1µF, R
MAXDTY
= 97.6kΩ, V
EN
= 0,
R
SCOMP
= 68kΩ, R
PRAMP
= 25kΩ, C
SKTON
= 0.01µF, C
SKTOFF
= 0.1µF, V
CS
= 0.6V, C
DRV
= 10pF,
T
A
= 0°C to +85°C,
unless otherwise
noted. Typical values are at T
A
= +25°C.)
PARAMETER
Fall Time
On-Resistance Pullup
On-Resistance Pulldown
SYNC (EXTERNAL FREQUENCY SYNCHRONIZATION)
Frequency Range
FREQ Input Threshold
THERMAL SHUTDOWN
Thermal Shutdown
T
A
rising, 20°C hysteresis
170
°C
Frequency syncs
±30%
of frequency set by external R
on FREQ pin
(Note 4)
0.2
2
1.0
3
MHz
V
CONDITIONS
C
DRV
= 500pF, 90% to 10% of V
VCC
C
DRV
= 2000pF, 90% to 10% of V
VCC
MIN
TYP
27
53
9
7
MAX
UNITS
ns
Ω
Ω
ELECTRICAL CHARACTERISTICS
(V
VCC
= 12V, C
REF
= 1µF, V
UV
= V
OV
= 2V, R
FREQ/SYNC
= 32.4kΩ, C
SS
= 0.1µF, R
MAXDTY
= 97.6kΩ, V
EN
= 0, R
SCOMP
= 68kΩ,
R
PRAMP
= 25kΩ, C
SKTON
= 0.01µF, C
SKTOFF
= 0.1µF, V
OPTO
= 2V, V
ILIM
= 4V, V
CS
= 0.6V, C
DRV
= 10pF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 5)
PARAMETER
V
CC
Operating Voltage Range
Undervoltage Lockout
Undervoltage Lockout Hysteresis
Supply Current
Shutdown Current
REF
Output Voltage
Load Regulation
Line Regulation
Shutdown Resistor
I
REF
= 0
I
REF
= 0 to 10mA
V
VCC
= 8.4V to 18V
V
EN
= 3V
V
UV
falling, 120mV typical hysteresis
V
UV
rising
V
OV
falling, 130 mV typical hysteresis
V
OV
rising
1.200
1.083
-0.5
2.901
2.778
4.9
5.1
50
20
30
1.300
1.173
+0.5
3.142
3.010
V
mV
mV
Ω
V
REF
= is active,
I
REF
= 0
V
EN
= 3V
No switching
Switching with no load
(Note 1)
V
CC
rising
V
CC
falling
7.6
7.6
6.6
0.9
4.2
6.3
0.9
18.0
8.4
7.4
V
V
V
mA
mA
CONDITIONS
MIN
TYP
MAX
UNITS
UNDERVOLTAGE/OVERVOLTAGE (UV/OV)
UVLO Threshold
Input Bias Current
OVLO Threshold
V
µA
V
4
_______________________________________________________________________________________
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