LM5041
Cascaded PWM Controller
General Description
The LM5041 PWM controller contains all of the features
necessary to implement either current-fed or voltage-fed
push-pull or bridge power converters. These "Cascaded"
topologies are well suited for multiple output and higher
power applications. The LM5041's four control outputs in-
clude: the buck stage controls (HD and LD) and the push-
pull control outputs (PUSH and PULL). Push-pull outputs are
driven at 50% nominal duty cycle at one half of the switching
frequency of the buck stage and can be configured for either
a guaranteed overlap time (for current-fed applications) or a
guaranteed both-off time (for voltage-fed applications).
Push-pull stage MOSFETs can be driven directly from the
internal gate drivers while the buck stage requires an exter-
nal driver such as the LM5102. The LM5041 includes a
high-voltage start-up regulator that operates over a wide
input range of 15V to 100V. The PWM controller is designed
for high-speed capability including an oscillator frequency
range up to 1 MHz and total propagation delays of less than
100ns. Additional features include: line Under-Voltage Lock-
out (UVLO), soft-start, an error amplifier, precision voltage
reference, and thermal shutdown.
Features
n
Internal Start-up Bias Regulator
n
Programmable Line Under-Voltage Lockout (UVLO) with
Adjustable Hysteresis
n
Current Mode Control
n
Internal Error Amplifier with Reference
n
Dual Mode Over-Current Protection
n
Leading Edge Blanking
n
Programmable Push-Pull Overlap or Dead Time
n
Internal 1.5A Push-Pull Gate Drivers
n
Programmable Soft-start
n
Programmable Oscillator with Sync Capability
n
Precision Reference
n
Thermal Shutdown
Applications
n
Telecommunication Power Converters
n
Industrial Power Converters
n
Multi-Output Power Converters
n
+42V Automotive Systems
Packages
n
TSSOP-16
n
LLP-16 (5x5 mm) Thermally Enhanced
Typical Application Circuit
20074901
Simplified Cascaded Push-Pull Power Converter
August 2003
LM5041
Cascaded
PWM
Controller
2003 National Semiconductor Corporation
DS200749
www.national.com
Connection Diagram
20074902
16-Lead TSSOP, LLP
Ordering Information
Order Number
Package Type
NSC Package Drawing
Supplied As
LM5041MTC
TSSOP-16
MTC-16
92 Units per anti-static tube
LM5041MTCX
TSSOP-16
MTC-16
2500 Units on Tape and Reel
LM5041SD
LLP-16
SDA-16A
Available Soon
LM5041SDX
LLP-16
SDA-16A
Available Soon
Pin Description
PIN
NAME
DESCRIPTION
APPLICATION INFORMATION
1
V
IN
Source Input Voltage
Input to start-up regulator. Input range 15V to 100V.
2
FB
Feedback Signal
Inverting input for the internal error amplifier. The
non-inverting input is connected to a 0.75V
reference.
3
COMP
Output of the Internal Error Amplifier
There is an internal 5k
resistor pull-up on this pin.
The error amplifier provides an active sink.
4
REF
Precision 5 volt reference output
Maximum output current: 10mA. Locally decouple
with a 0.1F capacitor. Reference stays low until the
line UV and the V
CC
UV are satisfied.
5
HD
Main Buck PWM control output
Buck switch PWM control output. The maximum duty
cycle clamp for this output corresponds to an off time
of typically 240ns per cycle. The LM5101 or LM5102
Buck stage gate driver can be used to level shift and
drive the Buck switch.
6
LD
Sync Switch control output
Sync Switch control output. Inversion of HD output.
The LM5101 or LM5102 lower drive can be used to
drive the synchronous rectifier switch.
7
V
CC
Output from the internal high voltage start-up
regulator. Regulated to 9 volts.
If an auxiliary winding raises the voltage on this pin
above the regulation setpoint, the internal start-up
regulator will shutdown, reducing the IC power
dissipation.
8
PUSH
Output of the push-pull drivers
Output of the push-pull gate driver. Output capability
of 1.5A peak .
LM5041
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2
Pin Description
(Continued)
PIN
NAME
DESCRIPTION
APPLICATION INFORMATION
9
PULL
Output of the push-pull drivers
Output of the push-pull gate driver. Output capability
of 1.5A peak.
10
PGND
Power ground
Connect directly to analog ground.
11
AGND
Analog ground
Connect directly to power ground.
12
CS
Current sense input
Current sense input to the PWM comparator (CM
control). There is a 50ns leading edge blanking on
this pin. Using separate dedicated comparators, if
CS exceeds 0.5V the outputs will go into cycle by
cycle current limit. If CS exceeds 0.6V the outputs
will be disabled and a soft-start commenced.
13
SS
Soft-start control
An external capacitor and an internal 10uA current
source, set the soft-start ramp. The controller will
enter a low power state if the SS pin is below the
shutdown threshold of 0.45V
14
TIME
Push-Pull overlap and dead time control
An external resistor sets the overlap time or dead
time for the push-pull outputs. A resistor connected
between TIME and GND produces overlap. A
resistor connected between TIME and REF produces
dead time.
15
RT / SYNC
Oscillator timing resistor pin and sync
An external resistor sets the oscillator frequency.
This pin will also accept an external oscillator.
16
UVLO
Line Under-Voltage Shutdown
An external divider from the power converter source
sets the shutdown levels. Threshold of operation
equals 2.5V. Hysteresis is set by a switched internal
current source (20A).
LM5041
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Block Diagram
Simplified Block Diagram
20074903
LM5041
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4
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
IN
to GND
100V
V
CC
to GND
16V
All Other Inputs to GND
-0.3 to 7V
Junction Temperature
150C
Storage Temperature
Range
-65C to +150C
ESD Rating
2 kV
Lead temperature (Note 2)
Wave
4 seconds
260C
Infrared
10 seconds
240C
Vapor Phase
75 seconds
219C
Operating Ratings
(Note 1)
V
IN
15 to 90V
Junction Temperature
-40C to +105C
Electrical Characteristics
Specifications with standard typeface are for T
J
= 25C, and those with boldface type apply over full Operating Junction
Temperature range. V
IN
= 48V, V
CC
= 10V, RT = 26.7k
, R
SET
= 20k
) unless otherwise stated (Note 3)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Startup Regulator
V
CC
Reg
V
CC
Regulation
open circuit
8.7
9
9.3
V
V
CC
Current Limit
(Note 4)
15
25
mA
I-V
IN
Startup Regulator
Leakage (external Vcc
Supply)
V
IN
= 100V
145
500
A
Shutdown Current (Iin)
UVLO = 0V, V
CC
= open
350
450
A
V
CC
Supply
V
CC
Under-voltage
Lockout Voltage
(positive going V
cc
)
V
CC
Reg
- 400mV
V
CC
Reg -
275mV
V
V
CC
Under-voltage
Hysteresis
1.7
2.1
2.6
V
Supply Current (I
CC
)
C
L
= 0
3
4
mA
Error Amplifier
GBW
Gain Bandwidth
3
MHz
DC Gain
80
dB
Input Voltage
V
FB
= COMP
0.735
0.75
0.765
V
COMP Sink Capability
V
FB
= 1.5V, COMP= 1V
4
8
mA
Reference Supply
V
REF
Ref Voltage
I
REF
= 0 mA
4.85
5
5.15
V
Ref Voltage
Regulation
I
REF
= 0 to 10mA
25
50
mV
Ref Current Limit
15
20
mA
Current Limit
ILIM Delay to Output
CS Step from 0 to 0.6V
Time to Onset of OUT
Transition (90%)
C
L
= 0
40
ns
Cycle by Cycle
Threshold Voltage
0.45
0.5
0.55
V
Cycle Skip Threshold
Voltage
Resets SS capacitor;
auto restart
0.55
0.6
0.65
V
Leading Edge
Blanking Time
50
ns
CS Sink Current
(clocked)
CS = 0.3V
2
5
mA
LM5041
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