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PDF LM5041MTC Data sheet ( Hoja de datos )
| Número de pieza | LM5041MTC | |
| Descripción | Cascaded PWM Controller | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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August 2003
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
Simplified Cascaded Push-Pull Power Converter
© 2003 National Semiconductor Corporation DS200749
20074901
www.national.com
1 page  
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN to GND
VCC to GND
All Other Inputs to GND
Junction Temperature
Storage Temperature
Range
100V
16V
-0.3 to 7V
150˚C
-65˚C to +150˚C
ESD Rating
2 kV
Lead temperature (Note 2)
Wave
4 seconds
Infrared
10 seconds
Vapor Phase
75 seconds
260˚C
240˚C
219˚C
Operating Ratings (Note 1)
VIN
Junction Temperature
15 to 90V
-40˚C to +105˚C
Electrical Characteristics
Specifications with standard typeface are for TJ = 25˚C, and those with boldface type apply over full Operating Junction
Temperature range. VIN = 48V, VCC = 10V, RT = 26.7kΩ, RSET = 20kΩ) unless otherwise stated (Note 3)
Symbol
Parameter
Conditions Min Typ
Max
Units
Startup Regulator
VCC Reg
I-VIN
VCC Regulation
VCC Current Limit
Startup Regulator
Leakage (external Vcc
open circuit
(Note 4)
VIN = 100V
8.7 9
15 25
145
9.3 V
mA
500 µA
Supply)
Shutdown Current (Iin)
VCC Supply
VCC Under-voltage
Lockout Voltage
UVLO = 0V, VCC = open
VCC Reg
- 400mV
350
VCC Reg -
275mV
450
µA
V
(positive going Vcc)
VCC Under-voltage
Hysteresis
1.7 2.1
2.6 V
Supply Current (ICC)
Error Amplifier
CL = 0
3 4 mA
GBW
Gain Bandwidth
3 MHz
DC Gain
80 dB
Input Voltage
COMP Sink Capability
Reference Supply
VFB = COMP
VFB = 1.5V, COMP= 1V
0.735
4
0.75
8
0.765
V
mA
VREF
Ref Voltage
Ref Voltage
Regulation
IREF = 0 mA
IREF = 0 to 10mA
4.85
5
25
5.15
50
V
mV
Ref Current Limit
15 20
mA
Current Limit
ILIM Delay to Output CS Step from 0 to 0.6V
40
ns
Time to Onset of OUT
Transition (90%)
Cycle by Cycle
CL = 0
0.45
0.5
0.55
V
Threshold Voltage
Cycle Skip Threshold Resets SS capacitor;
0.55
0.6
0.65
V
Voltage
auto restart
Leading Edge
50 ns
Blanking Time
CS Sink Current
CS = 0.3V
25
mA
(clocked)
5 www.national.com
5 Page 
Push-Pull Outputs (Continued)
PWM Comparator
The PWM comparator compares the slope compensated
current ramp signal to the loop error voltage from the internal
error amplifier (COMP pin). This comparator is optimized for
speed in order to achieve minimum controllable duty cycles.
The comparator polarity is such that 0V on the COMP pin will
produce zero duty cycle in the buck stage.
Error Amplifier
An internal high gain wide-bandwidth error amplifier is pro-
vided within the LM5041. The amplifier’s non-inverting input
is tied to a 0.75V reference. The inverting input is connected
to the FB pin. In non-isolated applications the power con-
verter output is connected to the FB pin via the voltage
setting resistors. Loop compensation components are con-
nected between the COMP and FB pins. For most isolated
applications the error amplifier function is implemented on
the secondary side of the converter and the internal error
amp is not used. The internal error amplifier is configured as
an open drain output and can be disabled by connecting the
FB pin to ground. An internal 5kΩ pull-up resistor between
the 5V reference and COMP can be used as the pull-up for
an opto-coupler in isolated applications.
Current Limit/Current Sense
The LM5041 contains two levels of over-current protection. If
the voltage at the CS pin exceeds 0.5V the present buck
stage duty cycle is terminated (cycle by cycle current limit). If
the voltage at the CS pin overshoots the 0.5V threshold and
exceeds 0.6V, then the controller will terminate the present
cycle and fully discharge the soft-start capacitor. A small RC
filter located near the controller is recommended to filter
current sense signals at the CS pin. An internal MOSFET
discharges the external CS pin for an additional 50ns at the
beginning of each cycle to reduce the leading edge spike
that occurs when the buck stage MOSFET is turned on.
The LM5041 current sense and PWM comparators are very
fast, and may respond to short duration noise pulses. Layout
considerations are critical for the current sense filter and
sense resistor. The capacitor associated with the CS filter
20074904
must be placed close to the device and connected directly to
the pins of the controller (CS and GND). If a current sense
transformer is used, both leads of the transformer secondary
should be routed to the sense resistor, which should also be
located close to the IC. A resistor may be used for current
sensing instead of a transformer, located in the push-pull
transistor sources, but a low inductance type of resistor is
required. When designing with a sense resistor, all of the
noise sensitive low power grounds should be connected
together around the IC and a single connection should be
made to the high current power ground (sense resistor
ground point).
The second level current sense threshold is intended to
protect the power converter by initiating a low duty cycle
hick-up mode when abnormally high currents are sensed. If
the second level threshold is reached, the soft-start capaci-
tor will be discharged and a start-up sequence will com-
mence when the soft-start capacitor is determined to be fully
discharged. The second level threshold will only be reached
when a high dV/dt is present at the current sense pin. The
current sense transient must be fast enough to reach the
second level threshold before the first threshold detector
turns off the buck stage driver. Very high current sense dV/dt
can occur with a saturated power inductor or shorted load.
Excessive filtering on the CS pin such as an extremely low
value current sense resistor or an inductor that does not
saturate with excessive loading, may prevent the second
level threshold from being reached. If the second level
threshold is never exceeded during an overload condition,
the first level current sense will continue cycle by cycle
limiting and the output characteristic of the converter will be
that of a current source. However, a sustained overload
current level can cause excessive temperatures in the power
train especially the output rectifiers.
Oscillator and Sync Capability
The LM5041 oscillator is set by a single external resistor
connected between the RT pin and GND. To set a desired
oscillator frequency (F), the necessary RT resistor can be
calculated from:
11 www.national.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LM5041MTC.PDF ] | |
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