TI LM25037QMTX/NOPB Lm25037/lm25037-q1 dual-mode pwm controller with alternating output Datasheet

LM25037, LM25037-Q1
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SNVS572D – JULY 2008 – REVISED MARCH 2013
LM25037/LM25037-Q1 Dual-Mode PWM Controller With Alternating Outputs
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FEATURES
DESCRIPTION
•
The LM25037 PWM controller contains all the
features necessary to implement balanced doubleended power converter topologies, such as push-pull,
half-bridge and full-bridge. These double-ended
topologies allow for higher efficiencies and greater
power densities compared to common single-ended
topologies such as the flyback and forward. The
LM25037 can be configured for either voltage mode
or current mode control with minimum external
components. Two alternating gate drive outputs are
provided, each capable of 1.2A peak output current.
The LM25037 can be configured to operate directly
from the input voltage rail over an ultra-wide range of
5.5V
to
75V.
Additional
features
include
programmable maximum duty cycle limit, line undervoltage lockout, cycle-by-cycle current limit and a
hiccup mode fault protection with adjustable timeout
delay, soft-start and a 2 MHz capable oscillator with
synchronization capability, precision reference and
thermal shutdown.
1
2
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•
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•
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LM25037-Q1 is an Automotive Grade Product
that is AEC-Q100 Grade 1 Qualified (-40°C to
125°C Operating Junction Temperature)
Ultra Wide Input Operating Range from 5.5V to
75V
Alternating Outputs for Double-ended
Topologies
Current-mode or Feed-forward Voltage-mode
Control
Programmable Maximum Duty Cycle Limit
2.0% Feedback Reference Accuracy
High Gain-bandwidth Error Amplifier
Programmable Line Under-voltage Lockout
(UVLO) with Adjustable Hysteresis
Versatile Dual Mode Over-current Protection
with Hiccup Delay Timer
Programmable Soft-start
Precision 5V Reference Output
Current Sense Leading Edge Blanking
Resistor Programmed 2 MHz Capable
Oscillator
Oscillator Synchronization Capability with Low
Frequency Lockout Protection
PACKAGE
•
16-Lead TSSOP
Simplified Push-Pull Power Converter
VIN
VOUT
LM25037
VIN
UVLO
VCC
OUTA
REF
OUTB
RT1
RAMP
RT2
CS
RES
COMP
SS
PGND
Isolated
Feedback
FB
AGND
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.
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SNVS572D – JULY 2008 – REVISED MARCH 2013
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Connection Diagram
1
16
VIN
UVLO
2
15
REF
COMP
3
14
VCC
FB
4
13
OUTA
RAMP
LM25037
RT2
5
12
OUTB
AGND
6
11
PGND
RT1
7
10
SS
CS
8
9
RES
Figure 1. Top View
16-Lead TSSOP Package
See PW Package
PIN DESCRIPTIONS
2
Pin
Name
Description
Application Information
1
RAMP
Pulse width modulator ramp
Modulation ramp for the PWM comparator. This ramp can be a representative
of the primary current (current mode) or proportional to input voltage (feedforward voltage mode). This pin is reset to ground at the conclusion of every
cycle by an internal FET.
2
UVLO
Line under-voltage lockout
An external voltage divider from the power source sets the shutdown and
standby comparator threshold levels. When UVLO exceeds the 0.45V
shutdown threshold, the VCC and REF regulators are enabled. When UVLO
exceeds the 1.25V standby threshold, the SS pin is released and the device
enters the active mode.
3
COMP
Input to the pulse width modulator
Output of the error amplifier and input to the PWM comparator.
4
FB
Feedback
Connected to inverting input of the error amplifier. An internal 1.25V reference
is connected to the non-inverting input of the error amplifier. In isolated
applications using an external error amplifier, this pin should be connected to
the AGND pin.
5
RT2
Oscillator dead-time control
The resistance connected between RT2 and AGND sets the forced dead-time
between switching periods of the alternating outputs.
6
AGND
Analog ground
Connect directly to Power Ground.
7
RT1
Oscillator maximum on-time control
The resistance connected between RT1 and AGND sets the oscillator
maximum on-time. The sum of this maximum on-time and the forced dead-time
(set by RT2) sets the oscillator period.
8
CS
Current sense input
If CS exceeds 250 mV the output pulse will be terminated, entering cycle-bycycle current limit. An internal switch holds CS low for 65 nS after either output
switches high to blank leading edge transients.
9
RES
Restart timer
If cycle-by-cycle current limit is reached during any cycle, a 18 µA current is
sourced to the external RES pin capacitor. If the RES capacitor voltage
reaches 2.0V, the soft-start capacitor will be fully discharged and then released
with a pull-up current of 1 uA. After the first output pulse (when SS = 1V), the
SS pin charging current will increase to the normal level of 100 µA.
10
SS
Soft-start
An external capacitor and an internal 100uA current source set the soft-start
ramp. The SS current source is reduced to 1 µA following a restart event (RES
pin high).
11
PGND
Power ground
Connect directly to Analog Ground
12
OUTB
Output driver
Alternating gate drive output of the pulse width modulator. Capable of 1.2A
peak source and sink current.
13
OUTA
Output driver
Alternating gate drive output of the pulse width modulator. Capable of 1.2A
peak source and sink current.
14
VCC
Output of the high voltage start-up
regulator. The VCC voltage is
regulated to 7.7V.
If an auxiliary winding raises the voltage on this pin above the regulation set
point, the internal start-up regulator will shutdown thus reducing the IC power
dissipation. Locally decouple VCC with a 0.47 µF or greater capacitor.
15
REF
Output of a 5V reference
Locally decouple with a 0.1 µF or greater capacitor. Maximum output current is
10 mA (typ).
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PIN DESCRIPTIONS (continued)
Pin
Name
16
VIN
Description
Application Information
Input voltage source
Input to the VCC Start-up regulator. Operating input range is 5.5V to 75V. For
power sources outside of this range, the LM25037 can be biased directly at
VCC by an external regulator.
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
-0.3V to 76V
VCC, RAMP , OUTA, OUTB to GND
-0.3V to 16V
CS to GND
-0.3V to 1.0V
UVLO, FB, RT2, RT1, SS, REF to GND
-0.3V to 7V
COMP, RES (3)
ESD Rating (4)
Human Body Model
2kV
Storage Temperature Range
−65°C to + 150°C
Junction Temperature
150°C
(1)
(2)
(3)
(4)
Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which
operation of the device is intended to be functional. For ensured specifications and test conditions, see the Electrical Characteristics.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
COMP, RES are output pins. As such, it is not recommended that external power sources be connected to these pins.
The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. 2kV for all pins.
Operating Ratings
VIN Voltage
5.5V to 75V
External Voltage Applied to VCC
8V to 14V
Operation Junction Temperature
−40°C to + 125°C
Electrical Characteristics
Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full operating junction
temperature range of −40°C to + 125°C. VVIN = 12V, VVCC = 10V, RRT1 = 30.1 kΩ, RRT2 = 30.1 kΩ, VUVLO = 3V unless
otherwise stated. (1) (2)
Symbol
Parameter
Conditions
Min
Typ
Max
7.7
8.1
Units
Startup Regulator (VCC Pin)
VCC voltage
IVCC = 10 mA
7.2
IVCC(Lim)
VVCC
VCC current limit
VVCC = 7V
20
VVCC(UV)
VCC Under-voltage threshold
4.6
Hysteresis
IVIN
5
5.4
0.5
Startup regulator current
Supply current into VCC from
external source
V
mA
V
V
VVIN = 20V, VUVLO = 0V
35
58
VVIN = 75V, VUVLO = 0V
45
80
Outputs & COMP open, VVCC = 10V,
Outputs switching
4
µA
µA
mA
Voltage Reference Regulator (REF Pin)
VREF
IREF(Lim)
REF Voltage
IREF = 0 mA
REF Voltage Regulation
IREF = 0 to 2.5 mA
REF Current Limit
VREF = 4.5V
VREF Under-Voltage Threshold
(1)
(2)
4.75
5
5.15
V
7
25
mV
5
10
3.7
4
mA
4.3
V
All limits are ensured. All electrical characteristics having room temperature limits are tested during production at TA = 25°C. All hot and
cold limits are ensured by correlating the electrical characteristics to process and temperature variations and applying statistical process
control.
Typical specifications represent the most likely parametric norm at 25°C operation.
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Electrical Characteristics (continued)
Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full operating junction
temperature range of −40°C to + 125°C. VVIN = 12V, VVCC = 10V, RRT1 = 30.1 kΩ, RRT2 = 30.1 kΩ, VUVLO = 3V unless
otherwise stated.(1)(2)
Symbol
VREF(UV)
Parameter
Conditions
Min
Hysteresis
Typ
Max
0.4
Units
V
Under-Voltage Lock Out and Shutdown (UVLO Pin)
VUVLO
Under-voltage threshold
IUVLO
Hysteresis current
UVLO pin sinking
Under-voltage Shutdown Threshold
UVLO voltage rising
1.20
1.25
1.295
V
17
22
26
µA
0.35
0.45
0.6
V
Hysteresis
0.1
V
Current Sense Input (CS Pin)
VCS
Current Limit Threshold
0.22
CS delay to output
CS from zero to 1V. Time for OUTA and
OUTB to fall to 90% of VCC. Output load =
0 pF.
Leading edge blanking time at CS
CS sink impedance (clocked)
Internal FET sink impedance
0.255
0.29
V
27
ns
65
ns
21
45
Ω
Current Limit Restart (RES Pin)
VRES
RES Threshold
1.9
2
2.2
V
Charge source current
VRES = 1.5V
14
18
21
µA
Discharge sink current
VRES = 1V
5
8
11
µA
Charging current in normal
operation
VSS = 0
70
100
130
µA
Charging current during a hiccup
mode restart
VSS = 0
0.6
1
1.4
µA
Soft-Stop Current Sink
VSS = 2.0V
70
100
130
µA
40
75
105
ns
Soft-Start (SS Pin)
ISS
Oscillator (RT1 and RT2 Pins)
DT1
Dead-Time 1
RRT2 = 15 kΩ
DT2
Dead-Time 2
RRT2 = 50 kΩ
FSW1
Frequency 1 (at OUTA, half
oscillator frequency)
RRT1 = 30.1 kΩ, RRT2 = 30.1 kΩ,
178
200
222
kHz
FSW2
Frequency 2 (at OUTA, half
oscillator frequency)
RRT1 = 11 kΩ, RRT2 = 30.1 kΩ,
448
515
578
kHz
250
DC level
ns
2
Input Sync threshold
2.5
3
V
3.4
V
PWM Controller (Comp Pin)
Delay to output
VPWM-OS
65
SS to RAMP offset
0.7
1
ns
1.2
V
0
%
Minimum duty cycle
VSS = 0V
COMP Open Circuit Voltage
VFB = 0V
4.5
4.75
5.0
V
COMP short circuit current
VFB = 0V, COMP = 0V
0.5
1
1.5
mA
5
20
Ω
Voltage Feed-Forward (RAMP Pin)
RAMP sink impedance(Clocked)
Error Amplifier
GBW
Gain Bandwidth
4
MHz
DC Gain
75
dB
Input Voltage
VFB = COMP
COMP sink capability
VFB = 1.5V COMP=1V
FB Bias Current
1.22
1.245
5
13
1.27
mA
V
10
nA
Main Output Drivers (OUTA and OUTB Pins)
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Electrical Characteristics (continued)
Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full operating junction
temperature range of −40°C to + 125°C. VVIN = 12V, VVCC = 10V, RRT1 = 30.1 kΩ, RRT2 = 30.1 kΩ, VUVLO = 3V unless
otherwise stated.(1)(2)
Symbol
Parameter
Conditions
Min
Typ
Vcc-0.5
Vcc0.25
Max
Units
Output high voltage
IOUT = 50 mA, (Source)
V
Output low voltage
IOUT = 100 mA (Sink)
0.2
Rise time
CLOAD = 1 nF
17
ns
Fall time
CLOAD = 1 nF
18
ns
Peak source current
VVCC = 10V
1.2
A
Peak sink current
VVCC = 10V
1.2
A
Thermal Shutdown Threshold
165
°C
Thermal Shutdown Hysteresis
25
°C
0.5
V
Thermal Shutdown
TSD
Thermal Resistance
θJC
Junction to Case
TSSOP
29
°C/W
θJA
Junction to Ambient
TSSOP
125
°C/W
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Typical Performance Characteristics
Typical Application Circuit Efficiency
VVCC and VREF
vs
VVIN
Figure 2.
Figure 3.
Start-Up Regulator Current (UVLO = 0)
VVCC
vs
IVCC
Figure 4.
Figure 5.
VREF
vs
IREF
Feedback Amplifier Gain/Phase
180
50
150
40
120
30
90
20
60
10
30
0
-10
0
-30
-20
-60
-30
-90
-40
-120
-50
-150
-60
10k
100k
1M
FREQUENCY
Figure 6.
6
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PHASE (o)
GAIN (dB)
60
-180
10M
Figure 7.
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Typical Performance Characteristics (continued)
Oscillator Frequency
vs
RT1
Dead-Time
vs
RT2
Figure 8.
Figure 9.
VFB
vs
Temperature
Oscillator Frequency
vs
Temperature
Figure 10.
Figure 11.
Dead-Time
vs
Temperature
Soft-Start and Restart Current
vs
Temperature
Figure 12.
Figure 13.
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Block Diagram
7.7V LDO
VCC
VIN
SHUTDOWN
0.45V
UVLO
5V
Reference
STANDBY
1.25V
REF
VCC/REF
UVLO
MODE
CONTROL
LOGIC
THERMAL LIMIT
( 165°C)
UVLO HYSTERESIS (22 PA)
VCC
RT1/SYNC
CLK
J
SET
Q
K
CLR
Q
DRIVER
OSCILLATOR
RT2
S
OUTA
Q
VCC
R
RAMP
1.25V
DRIVER
OUTB
ERROR
AMP
FB
+5V
PGND
5k
PWM
COMP
AGND
PWM
LOGIC
1V
SS
SS Buffer
2.0V
+5V
CS
0.25V
Hiccup
CLK + LEB
+5V
SS
SOFT-START
100 PA
CLK
Restart
Current
Source
Logic
18 PA
RES
+5V
RESTART DELAY
8 PA
1 PA
SS
Shutdown
100 PA
Standby
SOFT-STOP
Figure 14. Simplified Block Diagram
8
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Functional Description
The LM25037 PWM controller contains all the features necessary to implement double-ended power converter
topologies such as push-pull, half-bridge and full-bridge. The unique architecture allows the modulator to be
configured for either voltage-mode or current-mode control. The LM25037 provides two alternative gate driver
outputs to drive the primary side power MOSFETs with programmable forced dead-time. The LM25037 can be
configured to operate with bias voltages ranging from 5.5V to 75V. Additional features include line under-voltage
lockout, cycle-by-cycle current limit, voltage feed-forward compensation, and hiccup mode fault protection with
adjustable delays, soft-start, and a 2MHz capable oscillator with synchronization capability, precision reference
and thermal shutdown. These rich set of features simplify the design of double ended topologies. The functional
block diagram is shown in Figure 14.
HIGH-VOLTAGE START-UP REGULATOR
The LM25037 contains an internal high voltage, low drop-out start-up regulator that allows the input pin (VIN) to
be connected directly to the supply voltage over a range of 5.5V to a maximum of 75V. The regulator output at
VCC (7.7V) is internally current limited with a specified minimum of 20 mA. When the UVLO pin potential is
greater than 0.45V, the VCC regulator is enabled to charge an external capacitor connected to the VCC pin. The
VCC regulator provides power to the voltage reference (REF) and the gate drivers (OUTA and OUTB). When the
voltage on the VCC pin exceeds its Under Voltage (VCC UV) threshold of 5.0V nominal, the internal voltage
reference (REF) reaches its regulation set point of 5V and the UVLO voltage is greater than 1.25V, the controller
outputs are enabled. The value selected for the VCC capacitor depends on the total system design, and its startup characteristics. The recommended range of values for the VCC capacitor is 0.47 µF to 10 µF.The internal
power dissipation of the LM25037 can be reduced by powering VCC from an external supply. In typical
applications, an auxiliary transformer winding is connected through a diode to the VCC pin. This winding must
raise the VCC voltage above 8.2V to shut off the internal start-up regulator. Powering VCC from an auxiliary
winding improves efficiency while reducing the controller’s power dissipation. The VCC UV circuit will still function
in this mode, requiring that VCC never falls below 5.0V nominal during the start-up sequence. The VCC regulator
series pass transistor includes a diode between VCC and VIN that should not be forward biased in normal
operation. Therefore the auxiliary VCC voltage should never exceed the VIN voltage.
An external DC bias voltage can be used instead of the internal regulator by connecting the external bias voltage
to both the VCC and the VIN pins. In this particular case, the external bias must be greater than max VCC UV of
5.4V and less than the VCC maximum operating voltage rating (14V).
LINE UNDER-VOLTAGE DETECTOR
The LM25037 contains a dual level line Under-Voltage Lock Out (UVLO) circuit. When the UVLO pin voltage is
below 0.45V, the controller is in a low current shutdown mode. When the UVLO pin voltage is greater than 0.45V
but less than 1.25V, the controller is in standby mode. In standby mode the VCC and REF bias regulators are
active while the controller outputs are disabled. When the VCC and REF outputs exceed their respective undervoltage thresholds and the UVLO pin voltage is greater than 1.25V, the outputs are enabled and normal
operation begins. An external set-point voltage divider from VIN to GND can be used to set the minimum
operating voltage of the converter. The divider must be designed such that the voltage at the UVLO pin will be
greater than 1.25V when VIN enters the desired operating range. UVLO hysteresis is accomplished with an
internal 22 µA current source that is switched on or off into the impedance of the set-point divider. When the
UVLO pin voltage exceeds 1.25V threshold, the current source is activated to quickly raise the voltage at the
UVLO pin. When the UVLO pin voltage falls below the 1.25V threshold, the current source is disabled causing
the voltage at the UVLO pin to quickly fall. The hysteresis of the 0.45V shutdown comparator is internally fixed at
100 mV.
The UVLO pin can also be used to implement various remote enable/disable functions. Turning off the converter
by forcing the UVLO pin to standby condition provides a controlled soft-stop. See the SOFT-START section for
more details.
REFERENCE
The REF pin is the output of a 5V linear regulator that can be used to bias an opto-coupler transistor and
external housekeeping circuits. The regulator output is internally current limited to 10 mA (typical).
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ERROR AMPLIFIER
An internal high gain error amplifier is provided within the LM25037. The amplifier’s non-inverting reference is
tied to a 1.25V reference. In non-isolated applications the power converter output is connected to the FB pin via
the voltage setting resistors and loop compensation is connected between the COMP and FB pins. A typical
gain/phase plot is shown in Typical Performance Characteristics.
For most isolated applications the error amplifier function is implemented on the secondary side. Since the
internal error amplifier is configured as an open drain output, it can be disabled by connecting FB to ground. The
internal 5K pull-up resistor connected between the COMP pin and the 5V reference can be used as the pull-up
for an opto-coupler or other isolation device .
CYCLE-BY-CYCLE CURRENT LIMIT
The CS pin is to be driven by a signal representative of the transformer primary current. The current sense signal
can be generated by using a sense resistor or a current sense transformer. If the voltage sensed at the CS pin
exceeds 0.255V, the current sense comparator terminates the output driver pulse. If the high current condition
persists, the controller operates in a cycle-by-cycle current limit mode with duty cycle determined by the current
sense comparator instead of the PWM comparator. Cycle-by-cycle current limiting may eventually trigger the
hiccup mode restart cycle; depending on the configuration of the RES pin (see OVERLOAD PROTECTION
TIMER below). To suppress noise, a small R-C filter connected to the CS pin and located near the controller is
recommended. An internal 21Ω MOSFET discharges the external current sense filter capacitor at the conclusion
of every cycle. The discharge MOSFET remains on for an additional 65 ns after either OUTA or OUTB driver
switches high to blank leading edge transients in the current sensing circuit. Discharging the CS pin filter each
cycle and blanking leading edge spikes reduces the filtering requirements and improves the current sense
response time. The current sense comparator is 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 very close to the device and connected directly to the CS and AGND pins. If a sense
resistor located in the source of the main MOSFET switch is used for current sensing, a low inductance type of
resistor is required. When designing with a current sense resistor, all the noise sensitive, low power ground
connections should be connected together near the AGND pin, and a single connection should be made to the
power ground (sense resistor ground point).
OVERLOAD PROTECTION TIMER
The LM25037provides a current limit restart timer to disable the outputs and force a delayed restart (hiccup
mode) if a current limit condition is repeatedly sensed. The number of cycle-by-cycle current limit events required
to trigger the restart is programmed by the external capacitor at the RES pin. During each PWM cycle, the
LM25037 either sources to or sinks current from the RES pin capacitor. If no current limit is detected during a
cycle, a 8 µA discharge current sink is enabled to pull the RES pin towards ground. If a current limit is detected,
the 8 µA sink current is disabled and an 18 µA current source causes the voltage at the RES pin to gradually
increase. The LM25037 protects the converter with cycle-by-cycle current limiting while the voltage at RES pin
increases. If the RES voltage reaches the 2.0V threshold, the following restart sequence occurs (also see
Figure 15):
• The RES capacitor and SS capacitors are fully discharged.
• The soft-start current source is reduced from 100 µA to 1 µA.
• The SS capacitor voltage slowly increases. When the SS voltage reaches ≊1V, the PWM comparator will
produce the first narrow output pulse. After the first pulse occurs, the SS source current reverts to the normal
100 µA level. The SS voltage increases at its normal rate, gradually increasing the duty cycle of the output
drivers.
• If the overload condition persists after restart, cycle-by-cycle current limiting will begin to increase the voltage
on the RES capacitor again, repeating the hiccup mode sequence.
• If the overload condition no longer exists after restart, the RES pin will be held at ground by the 8 µA current
sink and normal operation resumes.
The overload timer function is very versatile and can be configured for the following modes of protection:
1. Cycle-by-cycle only: The hiccup mode can be completely disabled by connecting a zero to 50 kΩ resistor
from the RES pin to AGND. In this configuration, the cycle-by-cycle protection will limit the output current
indefinitely and no hiccup sequences will occur.
2. Hiccup only: The timer can be configured for immediate activation of a hiccup sequence upon detection of
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an overload by leaving the RES pin open circuit. In this configuration, the first detection of current limit
condition by the CS pin comparator will initiate a hiccup cycle with SS capacitor fully discharged and a
delayed restart.
3. Delayed Hiccup: Connecting a capacitor to the RES pin provides a programmed interval of cycle-by-cycle
limiting before initiating a hiccup mode restart, as previously described. The dual advantages of this
configuration are that a short term overload will not cause a hiccup mode restart but during extended
overload conditions, the average dissipation of the power converter will be very low.
4. Externally Controlled Hiccup: The RES pin can also be used as an input. By externally driving the pin to a
level greater than the 2.0V hiccup threshold, the controller will be forced into the delayed restart sequence.
For example, the external trigger for a delayed restart sequence could come from an over-temperature
protection circuit or an output over-voltage sensor
Current
Limit
CS
Current
Sense Circuit
5V
Restart
Current
Source Logic
0.25V
CLK
18 PA
RES
C RES
8 PA
SS
Voltage
Feedback
COMP
2.0V
To Output
Drivers
PWM
S
Drivers Off
+5V
Restart
Comparator
R Q
Restart
Latch
+5V
100 PA
CSS
SS
1PA
SS
Logic
100 mV
Drivers Off
Soft-start
LM25037
Figure 15. Current Limit Restart Circuit
Current Limit Detected
at CS
Current Limit Persists
2.0V
RES
0V
100 PA
5V
# 1V
SS
1 PA
OUTA
OUTB
t1
t2
t3
Figure 16. Current Limit Restart Timing
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SOFT-START
The soft-start circuit allows the regulator to gradually reach a steady state operating point, thereby reducing startup stresses and current surges. When bias is supplied to the LM25037, the SS pin capacitor is discharged by an
internal MOSFET. When the UVLO, VCC and REF pins reach their operating thresholds, the SS capacitor is
released and charged with a 100 µA current source. The PWM comparator control voltage at the COMP pin is
clamped to the SS pin voltage by an internal amplifier. When the PWM comparator input reaches 1V, output
pulses commence with slowly increasing duty cycle. The voltage at the SS pin eventually increases to 5V, while
the voltage at the PWM comparator increases to the value required for regulation as determined by the voltage
feedback loop.
One method to disable the regulator is to ground the SS pin. This forces the internal PWM control signal to
ground, reducing the output duty cycle quickly to zero. Releasing the SS pin initiates a soft-start sequence and
normal operation resumes. A second shutdown method is discussed in the UVLO DIVIDER SELECTION section.
PWM COMPARATOR
The pulse width modulation (PWM) comparator compares the voltage ramp signal at the RAMP pin to the loop
error signal. The loop error signal is derived from the internal error amplifier (COMP pin). The resulting control
voltage passes through a 1V level shift before being applied to the PWM comparator. This comparator is
optimized for speed in order to achieve minimum controllable duty cycles. The common mode input voltage
range of the PWM comparator is from 0 to 4.3V.
RAMP PIN
The voltage at the RAMP pin provides the modulation ramp for the PWM comparator. The PWM comparator
compares the modulation ramp signal at the RAMP pin to the loop error signal to control the output duty cycle.
The modulation ramp can be implemented either as a ramp proportional to input voltage, known as feed-forward
voltage mode control, or as a ramp proportional to the primary current, known as current mode control. The
RAMP pin is reset by an internal FET with an RDS(ON) of 5Ω (typical) at the end of every cycle. The ability to
configure the RAMP pin for either voltage mode or current mode allows the controller to be implemented for the
optimum control method for the selected power stage topology. Configuring RAMP pin is explained below and
the differences between voltage mode control and current mode control in various double-ended topologies is
explained in the Application Information section.
FEED-FORWARD VOLTAGE MODE
An external resistor (RFF) and capacitor (CFF) connected to VIN, AGND, and the RAMP pins is required to create
the PWM ramp signal as shown in Figure 17 below. It can be seen that the slope of the signal at RAMP will vary
in proportion to the input line voltage. This varying slope provides line feed-forward information necessary to
improve line transient response with voltage mode control. The RAMP signal is compared to the error signal by
the pulse width modulator comparator to control the duty cycle of the outputs. With a constant error signal, the
on-time (tON) varies inversely with the input voltage (VIN) to stabilize the Volt • Second product of the transformer
primary. At the end of clock period, an internal FET will be enabled to reset the CFF capacitor. The formulae for
RFF and CFF and component selection criteria are explained in the Application Information section. The amplitude
of the signal driving RAMP pin must not exceed the common mode input voltage range of the PWM comparator
(3.3V) while in normal operation.
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SLOPE
PROPORTIONAL
TO Vin
VIN
Vin
R FF
COMP
1V
Gate
Drive
RAMP
C FF
CLK
LM25037
Figure 17. Feed-Forward Voltage Mode Configuration
CURRENT MODE
The LM25037 can be configured for current mode control by injecting a signal representative of primary current
into the RAMP pin. One way to achieve this is shown in Figure 18. Filter components Rfilter and Cfilter are used to
filter leading edge noise spikes. The signal at the CS pin is thus a ramp on a pedestal. The pedestal corresponds
to the continuous conduction current in the transformer at the beginning of an OUTA or OUTB conduction cycle.
The R-C circuit (RSlope and CSlope), shown in Figure 18, tied to VREF adds an additional ramp to the current sense
signal. This additional ramp signal, known as slope compensation, is required to avoid instabilities at duty cycles
above 50% (25% per phase). The compensated RAMP signal consists of two parts, the primary current signal
and the slope compensation. The compensated RAMP signal is compared to the error signal by the PWM
comparator to control the duty cycle of the outputs. The RAMP capacitor and CS capacitor are reset through
internal discharge FETs. The RDS(ON) of RAMP discharge FET is 5Ω (typical); this ensures fast discharge of the
RAMP reset capacitor. Any dc voltage source can be used in place of VREF to generate the slope compensation
ramp.
The timing diagram shown in Figure 19 depicts the current mode waveforms and relative timing. When OUTA or
OUTB is enabled, the signal at the RAMP pin consists of the CS pin signal (current ramp on a pedestal) plus the
slope compensation ramp (dotted lines). When OUTA or OUTB is turned off, the primary current component is
absent but the voltage at the RAMP pin continues to rise due to slope compensation component until the end of
the clock period, after which it is reset by the RAMP discharge FET. A component selection example is explained
in detail in the Application Information section.
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V REF (5V)
R slope
RAMP
CLK
C slope
LM 25037
Current
Sense
R filter
cs
CLK + LEB
Rcs
C filter
Figure 18. Current Mode Configuration with Slope Compensation
CLK
CS
OUTA
OUTB
COMP
RAMP
Slope
Compensation
OUTPUT
OUTA
OUTB
Figure 19. Timing Diagram for Current Mode Configuration
OSCILLATOR
The LM25037 oscillator frequency and the maximum duty cycle are set by two external resistors connected
between the RT1 and RT2 pins to AGND. The minimum dead-time between OUTA and OUTB pulses is
proportional to the RT2 resistor value and the overall oscillator frequency is inversely proportional to RT1 and
RT2 resistor values. Each output switches at half the oscillator frequency. Initially, RT2 should be selected for the
desired dead-time or for the desired maximum duty cycle (Dmax).
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RT2 =
SNVS572D – JULY 2008 – REVISED MARCH 2013
Dead-Time
5.0 x 10
-12
50 ns<DT<250 ns
or
RT2 =
(1 - Dmax) / FOSC
5.0 x 10
-12
(1)
It is recommended to set the dead-time range between 50 ns and 250 ns. Beyond 250 ns, RT2 becomes
excessively large, and is prone to noise pickup. Fixed internal delays limit the dead-time to greater than 50 ns.
After the dead-time has been programmed by RT2, the overall oscillator frequency can be set by selecting
resistor RT1 from :
RT1 =
1
- (Dead-Time)
FOSC
0.162 x 10
-9
(2)
For example, if the desired oscillator frequency is 400 kHz (OUTA and OUTB each switching at 200 kHz) and
desired dead-time is 100 ns, the maximum duty cycle for each output will be 96% and the values of RT1 and
RT2 will be 15 kΩ and 20 kΩ respectively.
CLK
OUTA
Tonmax
OUTB
Tosc
TDead-Time
TDead-Time
Tonmax D RT1
TDead-Time D RT2
Figure 20. Timing Diagram of OUTA, OUTB and Dead-Time Set by RT2
As shown in Figure 20, the internal clock pulse width is the same as the dead-time set by RT2. This dead-time
pulse is used to limit the maximum duty cycle for each of the outputs. Also, the discharge FET connected to the
RAMP pin is enabled during the dead-time every clock period. The voltages at both the RT1 and RT2 pins are
internally regulated to a nominal 2V. Both the resistors RT1 and RT2 should be located as close as possible to
the IC, and connected directly to the pins. The tolerance of the external resistors and the frequency tolerance
indicated in Electrical Characteristics must be taken into account when determining the worst case frequency
range.
SYNC CAPABILITY
The LM25037 can be synchronized to an external clock by applying a narrow ac pulse to the RT1 pin. The
external clock must be at least 10% higher than the free-running oscillator frequency set by the RT1 and RT2
resistors. If the external clock frequency is less than the programmed frequency, the LM25037 will ignore the
synchronizing pulses. The synchronization pulse width at the RT1 pin must be a minimum of 15 ns wide. The
synchronization signal should be coupled into the RT1 pin through a 100 pF capacitor or another value small
enough to ensure the sync pulse width at RT1 is less than 60% of the clock period under all conditions. When
the synchronizing pulse transitions from low-to-high (rising edge), the voltage at the RT1 pin must be driven to
exceed 3.0V from its nominal 2.0V volt dc level. During the synchronization clock signal’s low time, the voltage at
the RT1 pin will be clamped at 2V volts by an internal regulator. The RT1 and RT2 resistors are always required,
whether the oscillator is free running or externally synchronized.
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GATE DRIVER OUTPUTS (OUTA & OUTB)
The LM25037 provides two alternating gate driver outputs, OUTA and OUTB. The internal gate drivers can each
source and sink 1.2A peak each. The maximum duty cycle is inherently limited to less than 50% and is based on
the value of RT2 resistor. As an example, if the COMP pin is in a high state, RT1 = 15K and RT2 = 20K then the
outputs will operate at maximum duty cycle of 96%.
THERMAL PROTECTION
Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event the maximum rated
junction temperature is exceeded. When activated, typically at 165°C, the controller is forced into a low power
standby state with the output drivers (OUTA and OUTB) and the bias regulators (VCC and REF) disabled. This
helps to prevent catastrophic failures from accidental device overheating. During thermal shutdown, the soft-start
capacitor is fully discharged and the controller follows a normal start-up sequence after the junction temperature
falls to the operating level (140°C).
APPLICATION INFORMATION
The following information is intended to provide guidelines for the design process when applying the LM25037.
TOPOLOGY and CONTROL ALGORITHM CHOICE
The LM25037 has all the features required to implement double-ended power converter topologies such as pushpull, half-bridge and full-bridge with minimum external components. One key feature is the flexibility in control
algorithm selection, i.e., the LM25037 can be used to implement either voltage mode control or current mode
control. Designers familiar with these topologies recognize that conventionally, current mode control is used for
push-pull and full-bridge topologies while voltage mode control is required for the half-bridge topology. In limited
applications, voltage mode control can be used for push-pull and full-bridge topologies as well, with special care
to maintain flux balance, such as using a dc-blocking capacitor in the primary (full-bridge). The goal of this
section is to illustrate implementation of both current mode control and voltage mode control using the LM25037
and aid the designer in the design process.
VOLTAGE MODE CONTROL USING THE LM25037
An external resistor (RFF) and capacitor (CFF) connected to VIN, AGND, and the RAMP pins is required to create
a saw-tooth modulation ramp signal shown in Figure 21. The slope of the signal at RAMP will vary in proportion
to the input line voltage. The varying slope provides line feed-forward information necessary to improve line
transient response with voltage mode control. With a constant error signal, the on-time (tON) varies inversely with
the input voltage (VIN) to stabilize the Volt • Second product of the transformer primary. Using a line feed-forward
ramp for PWM control requires very little change in the voltage regulation loop to compensate for changes in
input voltage, as compared to a fixed slope oscillator ramp. Furthermore, voltage mode control is less susceptible
to noise and does not require leading edge filtering, and is therefore a good choice for wide input range power
converters. Voltage mode control requires a more complicated compensation network, due to the complexconjugate poles of the L-C output filter.
In push-pull and full-bridge topologies, any asymmetry in the volt-second product applied to primary in one phase
may not be cancelled by subsequent phase, possibly resulting in a dc current build-up in the transformer, which
pushes the transformer core towards saturation. Special care in the transformer design, such as gapping the
core, or adding ballasting resistance in the primary is required to rectify this imbalance when using voltage mode
control with these topologies. Current mode control naturally corrects for any volt-second asymmetry in the
primary.
The recommended capacitor value range for CFF is 100 pF to 1500 pF. Referring to Figure 21, it can be seen
that value CFF must be small enough such that the capacitor can be discharged within the clock (CLK) pulse
width each cycle. The CLK pulse width is same as the dead-time set by RT2. The minimum possible dead-time
for LM25037 is 50 ns and the internal discharge FET RDS(ON) is 5Ω (typical),
The value of RFF required can be calculated from
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-1
RFF =
FOSC x CFF x In 1 -
VRAMP
VINmin
(3)
For example, assuming a VRamp of 1 volt at VINmin (a good compromise of signal range and noise immunity),
oscillator frequency, FOSC of 250 kHz, VINmin of 24 Volts, and CFF = 270 pF results in a value for RFF of 348 kΩ.
SLOPE
PROPORTIONAL
TO Vin
Vin
R FF
VIN
1V
COMP
Gate
Drive
RAMP
CLK
C FF
LM25037
Figure 21. Feed-Forward Voltage Mode Configuration
CURRENT MODE CONTROL USING THE LM25037
The LM25037 can be configured in current mode control by applying the primary current signal into the RAMP
pin. One way to achieve this is shown in Figure 22, which depicts a simplified push-pull converter. The primary
current is sensed using a sense resistor and the current information is then filtered and applied to the RAMP pin
through capacitor Cslope, for use as the modulation ramp. It can be seen that the signal applied to the RAMP pin
consists of the primary current information from the CS pin plus an additional ramp for slope compensation,
added by Rslope and Cslope.
VREF
Rslope
RAMP
+
Vin
CLK
Q2
Q1
-
Cslope
LM25037
CS
Rfilter
CLK + LEB
Current
Sense
RCS
Cfilter
Figure 22. Current Mode Configuration
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Current mode control inherently provides line voltage feed-forward, cycle-by-cycle current limiting and ease of
loop compensation as it removes the additional pole due to output inductor. Also, in push-pull and full-bridge
converters, current mode control inherently balances volt-second product in both the phases by varying the duty
cycle as needed to terminate the cycle at the same peak current for each output phase. For duty cycles greater
than 50% (25% for each phase), peak current mode controlled circuits are subject to sub-harmonic oscillation.
Sub-harmonic oscillation is normally characterized by observing alternating wide and narrow duty cycles at the
controller output. Adding an artificial ramp (slope compensation) to the current sense signal will eliminate this
potential oscillation. Current mode control is also susceptible to noise and layout considerations. It is
recommended that CFilter and Cslope be placed as close to the IC as possible to avoid any noise pickup and trace
inductance. When the converter is operating at low duty cycles and light load, the primary current amplitude is
small and is susceptible to noise. The artificial ramp, added to avoid sub-harmonic oscillations, provides
additional benefits by improving the noise immunity of the converter.
Configuration and component selection for current mode control is recommended as follows: The current sense
resistor is selected such that during over current condition, the voltage across the current sense resistor is above
the minimum CS threshold of 220 mV. It is recommended to set the impedances of RFilter and CFilter as seen from
Cslope at relatively low values, so that the slope compensation is primarily dictated by Rslope and Cslope
components. For example, if the filtering time (RFilter and CFilter) for leading edge noise is selected for 50 ns and if
the value selected for RFilter = 25Ω, then
CFilter =
50 x 10-9
3 x 25:
(4)
Resulting in a value of CFilter = 680 pF (approximated to a standard value). In general, the amount of slope
compensation required to avoid sub-harmonic oscillation is equal to at least one-half the down-slope of the
output inductor current, transformed to the primary. To mitigate sub-harmonic oscillation after one switching
period, the slope compensation has to be equal to one times the down slope of the filter inductor current
transformed to primary. This is known as deadbeat control. For circuits where primary current is sensed, the
amount of slope compensation for dead-beat control can be calculated from:
Slope-Comp =
Turns-Ratio x Vout x RCS
FOSC x Lfilter
(5)
Where, Turns-Ratio is referred with respect to the primary. For example, for a 5V output converter with a turns
ratio between secondary and primary of 1:2, an oscillator frequency (FOSC) of 250 kHz, a filter inductance of 4 µH
(LFilter) and a current sense resistor (RCS) of 32 mΩ, slope compensation of 80 mV will suffice. The slope
compensation "volts" that results from the above expression is the maximum voltage of the artificial ramp added
linearly to the RAMP pin till the end of maximum switching period. For circuits where a current sense
tramsformer is used for primary current sensing, the turns-ratio of the current sense transformer has to be taken
into account.
Cslope should be selected such that it can be fully discharged by the internal RAMP discharge FET. Capacitor
values ranging from 100 pF to 1500 pF are recommended. The value must be small enough such that the
capacitor can be discharged within the clock (CLK) pulse width each cycle.
Rslope can be selected from the following formula:
Rslope =
-1
FOSC x Cslope x In 1 -
- Rfilter
Slope-Comp
VREF
(6)
For example, with a Cslope of 1500 pF, FOSC of 250 kHz, reference voltage of 5V (VREF), slope compensation of
80 mV and Rfilter = 25Ω results in Rslope value of 165 kΩ.
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VIN and VCC
The voltage applied to the VIN pin, which may be the same as the system voltage applied to the power
transformer’s primary (VPWR), can vary in the range from 5.5V to 75V. The current into the VIN pin depends
primarily on the gate charge provided by the output drivers, the switching frequency, and any external loads on
the VCC and REF pins. It is recommended that the filter shown in Figure 23 be used to suppress transients that
may occur at the input supply. This is particularly important when VIN is operated close to the maximum
operating rating of the LM25037.
When power is applied to VIN and the UVLO pin voltage is greater than 0.45V, the VCC regulator is enabled and
supplies current into an external capacitor connected to the VCC pin. When the voltage on the VCC pin reaches
the regulation point of 7.7V, the voltage reference (REF) is enabled. The reference regulation set point is 5V. The
outputs (OUTA and OUTB) are enabled when the two bias regulators reach their set point and the UVLO pin
potential is greater than 1.25V. In typical applications, an auxiliary transformer winding is connected through a
diode to the VCC pin. This winding must raise the VCC voltage above 8.1V to shut off the internal start-up
regulator.
After the outputs are enabled and the external VCC supply voltage has begun supplying power to the IC, the
current into the VIN pin drops below 1 mA. VIN should remain at a voltage equal to or above the VCC voltage to
avoid reverse current through protection diodes.
VPWR
50
VIN
LM 25037
0.1 PF
Figure 23. Input Transient Protection
FOR APPLICATIONS WITH >75V INPUT
For applications where the system input voltage exceeds 75V or the IC power dissipation is of concern, the
LM25037 can be powered from an external start-up regulator as shown in Figure 24. In this configuration, the
VIN and the VCC pins should be connected together. The voltage at the VCC and VIN pins must be at least 5.5V
(> Max VCC UV voltage) yet not exceed 14V. An auxiliary winding can be used to reduce the power dissipation
in the external regulator once the power converter is active. The NPN base-emitter reverses breakdown voltage,
which can be as low as 5V for some transistors, should be considered when selecting the transistor.
5.5V to 14V
V PWR
VIN
VCC
from aux winding
LM25037
9V
Figure 24. Start-up Regulator for VPWR >75V
CURRENT SENSE
The CS pin should receive an input signal representative of the transformer’s primary current, either from a
current sense transformer or from a resistor in series with the source of the OUTA and OUTB MOSFET switches.
In both cases, the sensed current creates a voltage ramp across R1, and the RF/CF filter suppresses noise and
transients as shown in Figure 25 and Figure 26. R1, RF and CF should be located as close to the LM25037 as
possible, and the ground connection from the current sense transformer, or R1, should be a dedicated track to
the AGND pin. The current sense components must provide greater than 220 mV at the CS pin when an overcurrent condition exists.
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V PWR
Current Sense
Power Transformer
Q1
VIN
CS
RF
CF
LM25037
R1
AGND
Level
Shift
OUTA
Q2
OUTB
Figure 25. Current Sense Using Transformer
Power Transformer
VPWR
Vin
OUTA
Q1
Q2
OUTB
RF
CS
LM25037
CF
R1
Figure 26. Current Sense Using Current Sense Resistor (R1)
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UVLO DIVIDER SELECTION
A dedicated comparator connected to the UVLO pin detects an input under-voltage condition. When the UVLO
pin voltage is below 0.45V, the LM25037 controller is in a low current shutdown mode. For a UVLO pin voltage
greater than 0.45V but less than 1.25V, the controller is in standby mode with VCC and REF regulators active
but no switching. Once the UVLO pin voltage is greater than 1.25V, the controller is fully enabled. When the
UVLO pin voltage rises above the 1.25V threshold, an internal 22 µA current source as shown in Figure 27, is
activated thus providing threshold hysteresis. The 22 µA current source is deactivated when the voltage at the
UVLO pin falls below 1.25V. Resistance values for R1 and R2 can be determined from the following equations:
VHYS R1 =
R2 =
20 x 10-3 x VPWR
1.25
22 PA
1.25 x R1
VPWR - 1.25
(7)
Where VPWR is the desired turn-on voltage and VHYS is the desired UVLO hysteresis at VPWR.
LM25037
5.0V
VIN
22 PA
R1
1.25V
UVLO
STANDBY
R2
0.45V
SHUTDOWN
Figure 27. Basic UVLO Configuration
For example, if the LM25037 is to be enabled when VPWR reaches 33V, and disabled when VPWR decreases to
30V, R1 should be 113 kΩ, and R2 should be 4.42 kΩ. The voltage at the UVLO pin should not exceed 7V at
any time. Be sure to check both the power and voltage rating (0603 resistors can be rated as low as 50V) for the
selected R1 resistor. To maintain the UVLO threshold accuracy, a resistor tolerance of 1% or better is
recommended.
Remote control of the LM25037 operational modes can be accomplished with open drain device(s) connected to
the UVLO pin as shown in Figure 28.
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LM25037
5.0V
VIN
22 PA
R1
1.25V
UVLO
STANDBY
STANDBY
R2
OFF
0.45V
SHUTDOWN
Figure 28. Remote Standby and Disable Control
HICCUP MODE CURRENT LIMIT RESTART (RES)
The basic operation of the hiccup mode current limit is described in the functional description. The delay time to
the initiation of a hiccup cycle is programmed by the selection of the RES pin capacitor CRES as illustrated in
Figure 29.
Current Limit Detected
at CS
Current Limit Persists
2.0V
RES
0V
100 PA
5V
# 1V
SS
1 PA
OUTA
OUTB
t1
t3
t2
Figure 29. Hiccup Over-Load Restart Timing
In the case of continuous cycle-by-cycle current limit detection at the CS pin, the time required for CRES to reach
the 2.0V hiccup mode threshold is:
t1 =
CRES x 2.0V
18 PA
= 111k x CRES
(8)
For example, if CRES = 0.01 µF the time t1 is approximately 2.0 ms. The cool down time, t2 is set by the soft-start
capacitor (CSS) and the internal 1 µA SS current source, and is equal to:
t2 =
CSS x 1V
= 1M x CSS
1 PA
(9)
If CSS = 0.01 µF, t2 is ≊10 ms.
The soft-start time t3 is set by the internal 100 µA current source, and is equal to:
t3 =
22
CSS x 4V
= 40k x CSS
100 PA
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(10)
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If CSS = 0.01 µF, t3 is ≊ 400 µs.
The time t2 provides a periodic cool-down time for the power converter in the event of a sustained overload or
short circuit. This off time results in lower average input current and lower power dissipation within the power
components. It is recommended that the ratio of t2 / (t1 + t3) be in the range of 5 to 10 to take advantage of this
feature.
If the application requires no delay from the first detection of a current limit condition to the onset of the hiccup
mode (t1 = 0), the RES pin can be left open (no external capacitor). If it is desired to disable the hiccup mode
entirely, the RES pin should be connected to ground (AGND).
PRINTED CIRCUIT BOARD LAYOUT
The LM25037 Current Sense and PWM comparators are very fast, and respond to short duration noise pulses.
The components at the CS, COMP, SS, UVLO, RT2 and the RT1 pins should be as physically close as possible
to the IC, thereby minimizing noise pickup on the PC board trace inductances.
Layout considerations are critical for the current sense filter. If a current sense transformer is used, both leads of
the transformer secondary should be routed to the sense filter components and to the IC pins. The ground side
of the transformer should be connected via a dedicated PC board trace to the AGND pin, rather than through the
ground plane.
If the current sense circuit employs a sense resistor in the drive transistor source, low inductance resistors
should be used. In this case, all the noise sensitive, low-current ground trace should be connected in common
near the IC, and then a single connection made to the power ground (sense resistor ground point).
While employing current mode control, RAMP pin capacitor and CS pin capacitor must be placed close to the IC.
Also, a short direct trace should be employed to connect RAMP capacitor to the CS pin.
The gate drive outputs of the LM25037 should have short, direct paths to the power MOSFETs in order to
minimize inductance in the PC board The two ground pins (AGND, PGND) must be connected together with a
short, direct connection, to avoid jitter due to relative ground bounce.
If the internal dissipation of the LM25037 produces high junction temperatures during normal operation, the use
of multiple vias under the IC to a ground plane can help conduct heat away from the IC. Judicious positioning of
the PC board within the end product, along with use of any available air flow (forced or natural convection) will
help reduce the junction temperatures. If using forced air cooling, avoid placing the LM25037 in the airflow
shadow of tall components, such as input capacitors.
APPLICATION EXAMPLE
The following schematic shows an example of a 50W push-pull converter controlled by LM25037. The operating
input voltage range is 16V to 32V, and the output voltage is 5V. The output current capability is 10 Amps. The
converter is configured for current mode control with external slope compensation. An auxiliary winding of the
output filter inductor L3 is used to raise the VCC voltage to reduce the power dissipation.
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM25037 LM25037-Q1
Submit Documentation Feedback
23
LM25037, LM25037-Q1
SNVS572D – JULY 2008 – REVISED MARCH 2013
www.ti.com
Figure 30. Schematic
24
Submit Documentation Feedback
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM25037 LM25037-Q1
LM25037, LM25037-Q1
www.ti.com
SNVS572D – JULY 2008 – REVISED MARCH 2013
REVISION HISTORY
Changes from Revision C (March 2013) to Revision D
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 24
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM25037 LM25037-Q1
Submit Documentation Feedback
25
PACKAGE OPTION ADDENDUM
www.ti.com
11-Apr-2013
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
(2)
MSL Peak Temp
Op Temp (°C)
Top-Side Markings
(3)
(4)
LM25037MT/NOPB
ACTIVE
TSSOP
PW
16
92
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L25037
MT
LM25037MTX/NOPB
ACTIVE
TSSOP
PW
16
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L25037
MT
LM25037QMT/NOPB
ACTIVE
TSSOP
PW
16
92
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
M25037
MT
LM25037QMTX/NOPB
ACTIVE
TSSOP
PW
16
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
M25037
MT
(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)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a
continuation of the previous line and the two combined represent the entire Top-Side Marking for that device.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
11-Apr-2013
OTHER QUALIFIED VERSIONS OF LM25037, LM25037-Q1 :
• Catalog: LM25037
• Automotive: LM25037-Q1
NOTE: Qualified Version Definitions:
• Catalog - TI's standard catalog product
• Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
8-Apr-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LM25037MTX/NOPB
TSSOP
PW
16
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
LM25037QMTX/NOPB
TSSOP
PW
16
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
8-Apr-2013
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM25037MTX/NOPB
TSSOP
PW
16
2500
349.0
337.0
45.0
LM25037QMTX/NOPB
TSSOP
PW
16
2500
349.0
337.0
45.0
Pack Materials-Page 2
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