LM5041B
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SNVS605 – MAY 2009
LM5041B Cascaded PWM Controller
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FEATURES
DESCRIPTION
•
•
The LM5041B 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
LM5041B includes these four control outputs: 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 specified overlap time (for
current-fed applications) or a specified non-overlap
time (for voltage-fed applications). Push-pull stage
MOSFETs can be driven directly from the internal
gate drivers while the buck stage requires an external
driver such as the LM5102. The LM5041B 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 100 ns. Additional
features include line Under-Voltage Lock-Out
(UVLO), Soft-Start, an error amplifier, precision
voltage reference, and thermal shutdown.
1
2
•
•
•
•
•
•
•
•
•
•
Internal Start-up Bias Regulator
Programmable Line Under-Voltage Lockout
(UVLO) with Adjustable Hysteresis
Current Mode Control
Internal Error Amplifier with Reference
Cycle-by-cycle Over-Current Protection
Leading Edge Blanking
Programmable Push-Pull Overlap or Dead
Time
Internal 1.5A Push-Pull Gate Drivers
Programmable Soft-Start
Programmable Oscillator with Sync Capability
Precision Reference
Thermal Shutdown
APPLICATIONS
•
•
•
Telecommunication Power Converters
Industrial Power Converters
Multi-Output Power Converters
PACKAGES
•
•
TSSOP-16
WSON-16 (5x5 mm) Thermally Enhanced
The differences between LM5041, LM5041A and
LM5041B are as follows: In the LM5041A and the
LM5041B version, the hiccup mode over-current
protection is not employed and the VCC bias
regulator is not disabled by a low state at the SS pin.
In the LM5041B version, both the high and low side
buck stage gate drivers are forced to a low state
when the controller is disabled. In the LM5041 and
the LM5041B version, the buck stage controller is
disabled by either a low state at the UVLO pin or a
low state at the SS pin. Also in the LM5041B version,
the REF pin 5V regulator is not disabled by a UVLO
pin low state.
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2009, Texas Instruments Incorporated
LM5041B
SNVS605 – MAY 2009
www.ti.com
Typical Application Circuit
VOUT
33V - 76V
VDD
HB
VCC
VIN
HD
HI
HO
HS
LD
LM5041B
LI
RT
LM5102
2
VSS
LO
RT1 RT2
PUSH
FEED
BACK
PULL
FB
Figure 1. Simplified Cascaded Push-Pull Power Converter
Connection Diagram
1
2
3
4
5
6
7
8
VIN
UVLO
FB
RT
COMP
15
14
TIME
13
REF
SS
HD
CS
LD
AGND
VCC
PGND
PUSH
16
12
11
10
9
PULL
Figure 2. 16-Lead TSSOP, WSON
2
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PIN DESCRIPTIONS
Pin #
Pin
Name
1
VIN
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 5 kΩ resistor pull-up on this pin. The error amplifier provides an
active sink.
4
REF
Precision 5 volt
reference output
Maximum output current: 10 mA. Locally decouple with a 0.1 µF capacitor. Reference
stays low until the VCC 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 240 ns per cycle. The LM5101 or LM5102 Buck
stage gate driver can be used to level shift and drive the Buck switch MOSFET.
6
LD
Buck Sync Switch
control output
Sync Switch control output. Inversion of HD output during normal operation. The LM5101
or LM5102 lower drive can be used to drive the synchronous rectifier switch.
7
VCC
Output of the internal
high voltage start-up
regulator. Regulated to
9 volts.
If an auxiliary winding raises the voltage on this pin above the regulation set-point, 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 .
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 (current mode control). There is a 50 ns
leading edge blanking on this pin. If CS exceeds 0.5V, the PWM controller will go into
cycle by cycle current limit.
13
SS
Soft-Start control
An external capacitor and an internal 10 µA current source, set the soft-start ramp. Both
HD and LD will be forced to a low 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 (RSET) 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 source sets the shutdown levels. Threshold of
operation equals 2.5V. Hysteresis is set by a switched internal current source (20 µA).
Die substrate
The exposed die attach pad of the WSON package should be connected to a PCB
thermal pad at ground potential. For additional information on using TI's No Pull Back
WSON package, please refer to Application Note AN-1187 (literature number
SNOA401).
WSON
DAP
SUB
Pin
Description
Pin Application Information
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
ABSOLUTE MAXIMUM RATINGS (1) (2)
VIN to GND
100V
VCC to GND
16V
All Other Inputs to GND
-0.3 to 7V
Junction Temperature
150°C
Storage Temperature Range
-65°C to +150°C
ESD Rating (3)
Lead temperature
±2 kV
(4)
Wave
4 seconds at 260°C
Infrared
10 seconds at 240°C
Vapor Phase
75 seconds at 219°C
(1)
(2)
(3)
(4)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but does not ensure specific performance limits. For ensured specifications and conditions,
see the Electrical Characteristics.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Test Method is per JESD-22-A114.
For detailed information on soldering plastic TSSOP and WSON packages, please refer to Application Note AN-1520: A Guide to Board
Layout for Best Thermal Resistance for Exposed Packages (literature number SNVA183), Application Note AN-1187 (literature number
SNOA401), or go to www.ti.com/packaging for more information.
OPERATING RATINGS (1)
VIN
15 to 90V
Junction Temperature
(1)
-40°C to +125°C
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but does not ensure specific performance limits. For ensured specifications and conditions,
see the Electrical Characteristics.
ELECTRICAL CHARACTERISTICS
Unless otherwise stated the following conditions apply: VIN = 48V, VCC = 10V, RT = 26.7 kΩ, RSET = 20 kΩ. (1). Limits in
standard type are for TJ = 25°C only; limits in boldface type apply over the Operating Junction Temperature (TJ) range of 40°C to +125°C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values
represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
8.7
9
9.3
V
Startup Regulator
VCC Reg
VCC Regulation
VCC Current Limit
I-VIN
Open circuit
(1)
15
25
-
mA
Startup Regulator Leakage (external
VIN = 100V
Vcc Supply)
-
145
500
µA
Shutdown Current (Iin)
UVLO = 0V, VCC = open
-
350
450
µA
VCC Under-Voltage Lock-Out
Threshold
VCC rising
VCC Reg 400 mV
VCC Reg 275 mV
-
V
1.7
2.1
2.6
V
-
3
4
mA
VCC Supply
VCC Under-Voltage Lock-Out
Hysteresis
Supply Current (ICC)
(1)
4
CL = 0
Device thermal limitations may limit usable range.
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ELECTRICAL CHARACTERISTICS (continued)
Unless otherwise stated the following conditions apply: VIN = 48V, VCC = 10V, RT = 26.7 kΩ, RSET = 20 kΩ. (1). Limits in
standard type are for TJ = 25°C only; limits in boldface type apply over the Operating Junction Temperature (TJ) range of 40°C to +125°C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values
represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Error Amplifier
GBW
Gain Bandwidth
-
3
-
MHz
DC Gain
-
80
-
dB
0.735
0.75
0.765
V
4
8
-
mA
4.85
5
5.15
V
-
25
50
mV
15
20
-
mA
-
40
-
ns
0.45
0.5
0.55
V
-
50
-
ns
2
5
-
mA
Input Voltage
VFB = COMP
COMP Sink Capability
VFB = 1.5V, COMP= 1V
Reference Supply
VREF
Ref Voltage
IREF = 0 mA
Ref Voltage Regulation
IREF = 0 to 10 mA
Ref Current Limit
Current Limit
ILIM Delay to Output
CS Step from 0 to 0.6V
Time to Onset of OUT Transition
(90%)
CL = 0
Cycle by Cycle Threshold Voltage
Leading Edge Blanking Time
CS Sink Current (clocked)
CS = 0.3V
Soft-Start
Soft-Start Current Source
7
10
13
µA
Soft-Start to COMP Offset
0.35
0.55
0.75
V
Shutdown Threshold
0.25
0.5
0.75
V
Oscillator
Frequency1
RT = 26.7 kΩ
180
175
200
220
225
kHz
Frequency2
RT = 7.87 kΩ
515
600
685
kHz
-
3
3.5
V
Sync threshold
PWM Comparator
Delay to Output
COMP = 2V, CS stepped 0 to 0.4V
Time to onset of OUT transition low
-
25
-
ns
Max Duty Cycle
TS = Oscillator Period
-
(Ts-240ns)
/ Ts
-
%
Min Duty Cycle
COMP = 0V
-
-
0
%
-
0.32
-
COMP to PWM Comparator Gain
COMP Open Circuit Voltage
FB = 0V
4.1
4.8
5.5
V
COMP Short Circuit Current
FB = 0V, COMP = 0V
0.6
1
1.4
mA
-
110
-
mV
Under-Voltage Shutdown
2.44
2.5
2.56
V
Under-voltage Shutdown
Hysteresis Current Source
16
20
24
µA
Slope Compensation
Slope Comp Amplitude
Delta increase at PWM Comparator
to CS
UVLO Shutdown
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ELECTRICAL CHARACTERISTICS (continued)
Unless otherwise stated the following conditions apply: VIN = 48V, VCC = 10V, RT = 26.7 kΩ, RSET = 20 kΩ. (1). Limits in
standard type are for TJ = 25°C only; limits in boldface type apply over the Operating Junction Temperature (TJ) range of 40°C to +125°C. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values
represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Buck Stage Outputs
Output High level
-
5 (VREF)
-
V
Output High Saturation
IOUT = 10 mA, REF = VOUT
-
0.5
1
V
Output Low Saturation
IOUT = −10 mA
-
0.5
1
V
Rise Time
CL = 100 pF
-
10
-
ns
Fall Time
CL = 100 pF
-
10
-
ns
Push-Pull Outputs
Overlap Time
RSET = 20 kΩ Connected to GND,
50% to 50% Transitions
60
90
120
ns
Dead Time
RSET = 20kΩ Connected to REF,
50% to 50% Transitions
65
95
125
ns
Output High Saturation
IOUT = 50 mA
VCC - VOUT
-
0.25
0.5
V
Output Low Saturation
IOUT = 100 mA
-
0.5
1
Rise Time
CL = 1 nF
-
20
Fall Time
CL = 1 nF
-
20
-
ns
Thermal Shutdown Temp.
-
165
-
°C
Thermal Shutdown Hysteresis
-
25
-
°C
TSSOP Package
-
125
-
°C/W
WSON Package
-
32
-
°C/W
V
ns
Thermal Shutdown
TSD
Thermal Resistance
θJA
6
Thermal Resistance
Junction to Ambient
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TYPICAL PERFORMANCE CHARACTERISTICS
VCC and VIN
vs
VIN
20
VCC
vs
ICC
10
VIN
8
VIN = 15V
6
VCC (V)
VCC AND VIN (V)
15
VCC
10
4
5
2
0
0
5
0
15
10
0
20
5
10
15
20
25
ICC (mA)
VIN (V)
SS Pin Current
vs
Temp
Frequency
vs
RT
1000
13
FREQUENCY (kHz)
SS CURRENT (PA)
12
11
10
9
8
100
7
-25
25
75
10000
1000
125
TEMPERATURE (oC)
Overlap Time
vs
RSET
Dead Time
vs
RSET
500
500
400
400
DEAD TIME (ns)
OVERLAP TIME (ns)
100000
RT (:)
300
200
300
200
100
100
0
0
10
30
50
70
90
110
10
30
50
70
90
110
RSET (k:)
RSET (k:)
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Dead Time
vs
Temp
120
130
110
120
DEAD TIME (ns)
OVERLAP TIME (ns)
Overlap Time
vs
Temp
100
RSET = 20k:
90
80
110
RSET = 20k:
100
70
90
80
70
60
-25
25
75
125
TEMPERATURE (oC)
-25
25
75
125
TEMPERATURE (oC)
Error Amplifier Gain Phase
8
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BLOCK DIAGRAM
9V SERIES
REGULATOR
VIN
VCC
5V
REFERENCE
VCC
ENABLE
UVLO
UVLO SHUTDOWN
+
-
2.5V
VREF
UVLO
LOGI
C
UVLO
HYSTERESIS
(20 PA)
45 PA
CLK
COMP
0.75V
5k
FB
PWM
100k
+
-
SLOPE COMP
RAMP
GENERATOR
S
Q
R
Q
+
-
1.4V
50k
LOGIC
SS
CS
2k
HD
c
5V
LD
UVLO SHUTDOWN
SS SHUTDOWN
+
-
0.5V
PGND
CLK + LEB
AGND
10 PA
SS
SS
TIME
0.45V
+
-
SS SHUTDOWN
VCC
DRIVE
R
OSC
CLK
RT / SYNC
OSCILLATOR
DIVIDE BY 2
OVERLAP
OR
DEAD TIME
CONTROL
PUSH
VCC
DRIVE
R
PULL
Figure 3. Simplified Block Diagram
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DETAILED OPERATING DESCRIPTION
The LM5041B PWM controller contains all of the features necessary to implement either current-fed or voltagefed push-pull or bridge power converters. These “Cascaded” topologies are well suited for multiple output and
higher power applications. The LM5041B includes these four control outputs: 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 specified overlap time
(for current-fed applications) or a specified non-overlap time (for voltage-fed applications). Push-pull stage
MOSFETs can be driven directly from the internal gate drivers while the buck stage requires an external driver
such as the LM5102. The LM5041B 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 100 ns. Additional features include line UnderVoltage Lock-Out (UVLO), Soft-Start, an error amplifier, precision voltage reference, and thermal shutdown.
High Voltage Start-Up Regulator
The LM5041B contains an internal high-voltage start-up regulator, thus the input pin (Vin) can be connected
directly to the line voltage. The regulator output is internally current limited to 15 mA. When power is applied, the
regulator is enabled and sources current into an external capacitor connected to the Vcc pin. The recommended
capacitance range for the Vcc regulator is 0.1µF to 100 µF. When the voltage on the Vcc pin reaches the
regulation point of 9V, the internal voltage reference (REF) reaches its regulation point of 5V, and the soft-start
capacitor is charged above its shutdown threshold, the controller outputs are enabled. The Buck stage outputs
will remain enabled until Vcc falls below 7V, the REF pin voltage falls below approximately 3V, the SS pin is
forced below the 0.45V shutdown threshold or the line Under-Voltage Lock-Out detector indicates that Vin is out
of range. The push-pull outputs continue switching until the REF pin voltage falls below approximately 3V. In
typical applications, an auxiliary transformer winding is connected through a diode to the Vcc pin. This winding
must raise the Vcc voltage above 9.3V to shut off the internal start-up regulator. Powering VCC from an auxiliary
winding improves efficiency while reducing the controller's power dissipation. The recommended capacitance
range for the Vref regulator output is 0.1µF to 10 µF.
The external VCC capacitor must be sized such that the capacitor maintains a VCC voltage greater than 7V during
the initial start-up. During a fault mode when the converter auxiliary winding is inactive, external current draw on
the VCC line should be limited so the power dissipated in the start-up regulator does not exceed the maximum
power dissipation of the controller.
An external start-up or other bias rail can be used instead of the internal start-up regulator by connecting the VCC
and the VIN pins together and feeding the external bias voltage into the two pins.
Line Under-Voltage Detector
The LM5041B contains a line Under-Voltage Lock-Out (UVLO) circuit. An external set-point resistor divider from
VIN to ground sets the operational range of the converter. The divider must be designed such that the voltage at
the UVLO pin will be greater than 2.5V when VIN is in the desired operating range. If the Under-Voltage threshold
is not met, both HD and LD will be forced to low state and VCC regulator will be disabled while the push-pull
outputs continue switching until the REF pin voltage falls below approximately 3V. ULVO hysteresis is
accomplished with an internal 20 µA current source that is switched on or off into the impedance of the set-point
divider. When the UVLO threshold is exceeded, the current source is activated to instantly raise the voltage at
the UVLO pin. When the UVLO pin falls below the 2.5V threshold, the current source is turned off causing the
voltage at the UVLO pin to fall. The UVLO pin can also be used to implement a remote enable / disable function.
By shorting the UVLO pin to ground, the converter can be disabled.
Buck Stage Control Outputs
The LM5041B Buck switch maximum duty cycle clamp ensures that there will be sufficient off time each cycle to
recharge the bootstrap capacitor used in the high side gate driver. The Buck switch is specified to be off, and the
sync switch on, for at least 250 ns per switching cycle. The Buck stage control outputs (LD and HD) are CMOS
buffers with logic levels of 0 to 5V.
During any fault state or Under-Voltage off state, both HD and LD state will be forced to low by the buck stage
control.
10
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Push-Pull Outputs
The push pull outputs operate continuously at a nominal 50% duty cycle. A distinguishing feature of the
LM5041B is the ability to accurately configure either dead time (both-off) or overlap time (both-on) on the
complementary push-pull outputs. The overlap/dead time magnitude is controlled by a resistor connected to the
TIME pin on the controller. The TIME pin holds one end of the resistor at 2.5V and the other end of the resistor
should be connected to either REF for dead time control setting or to GND for overlap control. The polarity of the
current in the TIME is detected by the LM5041B The magnitude of the overlap/dead time can be calculated as
follows:
Overlap Time (ns) = (3.66 x RSET) + 7
Overlap Time in ns, RSET connected to GND, RSET in kΩ
Dead Time (ns) = (3.69 x RSET) + 21
Dead Time in ns, RSET connected to REF, RSET in kΩ
Recommended RSET programming range: 10 kΩ to 100 kΩ
Current-fed designs require a period of overlap to insure there is a continuous path for the buck inductor current.
Voltage-fed designs require a period of dead time to insure there is no time when the push-pull transformer acts
as a shorted turn to the low impedance sourcing node. The push-pull outputs alternate continuously under all
conditions provided REF the voltage is greater than 3V.
K1 * RSET
PUSH
DEADTIME
WAVEFORMS
K1 * RSET
PULL
K2 * RSET
PUSH
OVERLAP
WAVEFORMS
K2 * RSET
PULL
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 provided within the LM5041B. 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 converter output is connected to the FB pin via the voltage setting resistors. Loop compensation
components are connected 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 5 kΩ pull-up resistor between the 5V reference and the COMP pin can be used as the pull-up
for an opto-coupler in isolated applications.
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Current Limit/Current Sense
The LM5041B provides cycle-by-cycle over-current protection. If the voltage at the CS comparator (CS pin
voltage plus slope comp voltage) exceeds 0.5V the present buck stage duty cycle is terminated (cycle by cycle
current limit). 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 50 ns at the beginning of each
cycle to reduce the leading edge spike that occurs when the buck stage MOSFET is turned on.
The LM5041B 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 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).
Oscillator and Sync Capability
The LM5041B 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:
RT =
(1/F) - 235 x 10-9
:
182 x 10-12
(1)
The buck stage will switch at the oscillator frequency and each push-pull output will switch at half the oscillator
frequency in a push-pull configuration. The LM5041B can also be synchronized to an external clock. The external
clock must have a higher frequency than the free running frequency set by the RT resistor. The clock signal
should be capacitively coupled into the RT pin with a 100 pF capacitor. A peak voltage level greater than 3V is
required for detection of the sync pulse. The sync pulse width should be set in the 15 ns to 150 ns range by the
external components. The RT resistor is always required, whether the oscillator is free running or externally
synchronized. The voltage at the RT pin is internally regulated to 2V. The RT resistor should be located very
close to the device and connected directly to the pins of the IC (RT and GND).
Slope Compensation
The PWM comparator compares the current sense signal to the voltage at the COMP pin. The output stage of
the internal error amplifier generally drives the COMP pin. At duty cycles greater than 50%, current mode control
circuits are subject to sub-harmonic oscillation. By adding an additional fixed ramp signal (slope compensation)
to the current sense ramp, oscillations can be avoided. The LM5041B integrates this slope compensation by
buffering the internal oscillator ramp and summing a current ramp generated by the oscillator internally with the
current sense signal. Additional slope compensation may be provided by increasing the source impedance of the
current sense signal.
Soft-Start and Shutdown
The soft-start feature allows the power converter to gradually reach the initial steady state operating point,
thereby reducing start-up stresses and surges. At power on, a 10 µA current is sourced out of the soft-start pin
(SS) to charge an external capacitor. The capacitor voltage will ramp up slowly and will limit the maximum duty
cycle of the buck stage. In the event of a fault as indicated by VCC Under-voltage, line Under-voltage the output
drivers are disabled and the soft-start capacitor is discharged to 0.7V. When the fault condition is no longer
present, a soft-start sequence will begin again and buck stage duty cycle will gradually increase as the soft-start
capacitor is charged.
The SS pin also serves as an enable input of HD and LD. Both HD and LD will be forced to a low state if the SS
pin is below the shutdown threshold of 0.45V.
12
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LM5041B
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SNVS605 – MAY 2009
Thermal Protection
Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event that the maximum
junction temperature is exceeded. When activated, typically at 165 degrees Celsius, the controller is forced into a
low-power standby state, disabling the output drivers and the bias regulator. This feature is provided to prevent
catastrophic failures from accidental device overheating.
Differences Between LM5041, LM5041A and LM5041B
There are five differences between LM5041, LM5041A and LM5041B. In the LM5041A and the LM5041B
versions, the hiccup mode over-current protection is not employed and the VCC bias regulator is not disabled by
SS pin shutdown state. In the LM5041B version, both HD and LD will be low state when the PWM controller
disabled. In the LM5041 and the LM5041B version, PWM controller is disabled by either a UVLO pin low state or
SS pin shutdown state. Also in the LM5041B version, the REF pin output is not disabled by a UVLO pin low
state. However, if VCC does not receive power from an external source, the UVLO pin low state will disable the
internal VCC regulator and a VCC under-voltage condition will eventually disable REF as the VCC voltage falls.
Differences Between LM5041, LM5041A and LM5041B
ITEM
LM5041
LM5041A
LM5041B
Hiccup mode over-current protection
Available
N/A
N/A
VCC disabled by SS shutdown
Yes
No
No
REF disabled by UVLO pin low state
Yes
Yes
No
BUCK controller disabled by SS shutdown
Yes
No
Yes
BUCK driver states when the controller disabled
HD : LOW
LD :HIGH
HD : LOW
LD : HIGH
HD : LOW
LD : LOW
Logic Table
MODE
CONTROLS
UVLO
SS
PIN STATES
DEVICE
VCC
REF
HD
LD
PUSH&PULL
9V
5V
PWM
PWM
50% Duty Cycle
GND
GND
LOW
LM5041
Normal
Operation
HIGH
-
LM5041A
LM5041B
LM5041
UVLO
Shutdown
LOW
-
LM5041A
LM5041B
LM5041
SS
Shutdown
HIGH
LOW
LM5041B
LOW
LOW
GND
LM5041A
HIGH
9V
GND
5V
LOW
HIGH
LOW
LOW
50% Duty Cycle
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Product Folder Links: LM5041B
13
LM5041B
SNVS605 – MAY 2009
www.ti.com
Typical Application
VOUT
T1
L1
33V - 76V
VDD
VDD
HB
VCC
VIN
HB
HD
HO
+
HI
HO
HI
T1
HS
HS
LD
LI
+
LI
LO
LM5102
LM5041B
VSS
LO
LM5100
RT2
RT1
PUSH
PULL
COMP
FEED
BACK
Figure 4. Simplified Cascaded Half-Bridge
14
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Product Folder Links: LM5041B
LM5041B
www.ti.com
SNVS605 – MAY 2009
Application Circuit: Input 35V to 80V, Output 2.5V, 50A
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Copyright © 2009, Texas Instruments Incorporated
Product Folder Links: LM5041B
15
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM5041BMTC/NOPB
ACTIVE
TSSOP
PW
16
92
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM5041B
MTC
LM5041BMTCX/NOPB
ACTIVE
TSSOP
PW
16
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
LM5041B
MTC
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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