TI1 LM5025A Active clamp voltage mode pwm controller Datasheet

LM5025A
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SNVS293D – DECEMBER 2004 – REVISED MARCH 2010
LM5025A Active Clamp Voltage Mode PWM Controller
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FEATURES
1
•
•
•
2
•
•
•
Internal Start-up Bias Regulator
3A Compound Main Gate Driver
Programmable Line Under-Voltage Lockout
(UVLO) with Adjustable Hysteresis
Voltage Mode Control with Feed-Forward
Adjustable Dual Mode Over-Current Protection
Programmable Overlap or Deadtime between
•
•
•
•
•
•
•
the Main and Active Clamp Outputs
Volt x Second Clamp
Programmable Soft-start
Leading Edge Blanking
Single Resistor Programmable Oscillator
Oscillator UP / DOWN Sync Capability
Precision 5V Reference
Thermal Shutdown
DESCRIPTION
The LM5025A is a functional variant of the LM5025 active clamp PWM controller. The functional differences of
the LM5025A are: The CS1 and CS2 current limit thresholds have been increased to 0.5V. The internal CS2 filter
discharge device has been disabled and no longer operates each clock cycle. The internal VCC and VREF
regulators continue to operate when the line UVLO pin is below threshold.
The LM5025A PWM controller contains all of the features necessary to implement power converters utilizing the
Active Clamp / Reset technique. With the active clamp technique, higher efficiencies and greater power densities
can be realized compared to conventional catch winding or RDC clamp / reset techniques. Two control outputs
are provided, the main power switch control (OUT_A) and the active clamp switch control (OUT_B). The two
internal compound gate drivers parallel both MOS and Bipolar devices, providing superior gate drive
characteristics. This controller is designed for high-speed operation including an oscillator frequency range up to
1MHz and total PWM and current sense propagation delays less than 100ns. The LM5025A includes a highvoltage start-up regulator that operates over a wide input range of 13V to 90V. Additional features include: Line
Under Voltage Lockout (UVLO), softstart, oscillator UP/DOWN sync capability, precision reference and thermal
shutdown.
Packages
•
•
TSSOP-16
LLP-16 (5x5 mm) Thermally Enhanced
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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LM5025A
SNVS293D – DECEMBER 2004 – REVISED MARCH 2010
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Typical Application Circuit
VOUT
3.3V
VIN
35 - 78V
LM5025A
ERROR
AMP &
ISOLATION
CS1
VIN
VCC
UVLO
OUT_A
OUT_B
RAMP COMP
REF
CS2
SYNC
Rt
TIME
SS
PGND AGND
UP/DOWN
SYNC
Figure 1. Simplified Active Clamp Forward Power Converter
Connection Diagram
VIN
1
16
UVLO
RAMP
2
15
SYNC
CS1
3
14
RT
CS2
4
13
COMP
TIME
5
12
SS
REF
6
11
AGND
VCC
7
10
PGND
OUT_A
8
9
OUT_B
Figure 2. 16-Lead TSSOP, LLP
Pin Functions
Pin Description
2
Pin
Name
Description
Application Information
1
VIN
Source Input Voltage
Input to start-up regulator. Input range 13V to 90V, with
transient capability to 105V.
2
RAMP
Modulator ramp signal
An external RC circuit from Vin sets the ramp slope. This
pin is discharged at the conclusion of every cycle by an
internal FET, initiated by either the internal clock or the
V*Sec Clamp comparator.
3
CS1
Current sense input for cycle-by-cycle limiting
If CS1 exceeds 0.5V the outputs will go into Cycle-byCycle current limit. CS1 is held low for 50ns after OUT_A
switches high providing leading edge blanking.
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Pin Description (continued)
Pin
Name
4
CS2
Current sense input for soft restart
Description
If CS2 exceeds 0.5V the outputs will be disabled and a
softstart commenced. The soft-start capacitor will be fully
discharged and then released with a pull-up current of
1µA. After the first output pulse (when SS =1V), the SS
charge current will revert back to 20µA.
Application Information
5
TIME
Output overlap/Deadtime control
An external resistor (RSET) sets either the overlap time or
dead time for the active clamp output. An RSET resistor
connected between TIME and GND produces in-phase
OUT_A and OUT_B pulses with overlap. An RSET resistor
connected between TIME and REF produces out-of-phase
OUT_A and OUT_B pulses with deadtime.
6
REF
Precision 5 volt reference output
Maximum output current: 10mA Locally decouple with a
0.1µF capacitor. Reference stays low until the VCC UV
comparator is satisfied.
7
VCC
Output from the internal high voltage start-up
regulator. The VCC voltage is regulated to 7.6V.
If an auxiliary winding raises the voltage on this pin above
the regulation setpoint, the internal start-up regulator will
shutdown, reducing the IC power dissipation.
8
OUT_A
Main output driver
Output of the main switch PWM output gate driver. Output
capability of 3A peak sink current.
9
OUT_B
Active Clamp output driver
Output of the Active Clamp switch gate driver. Capable of
1.25A peak sink current..
10
PGND
Power ground
Connect directly to analog ground.
11
AGND
Analog ground
Connect directly to power ground. For the LLP package
option the exposed pad is electrically connected to AGND.
12
SS
Soft-start control
An external capacitor and an internal 20µA current source
set the softstart ramp. The SS current source is reduced to
1uA initially following a CS2 over-current event or an over
temperature event.
13
COMP
Input to the Pulse Width Modulator
An internal 5KΩ resistor pull-up is provided on this pin. The
external opto-coupler sinks current from COMP to control
the PWM duty cycle.
14
RT
Oscillator timing resistor pin
An external resistor connected from RT to ground sets the
internal oscillator frequency.
15
SYNC
Oscillator UP/DOWN synchronization input
The internal oscillator can be synchronized to an external
clock with a frequency 20% lower than the internal
oscillator’s free running frequency. There is no constraint
on the maximum sync frequency.
16
UVLO
Line Under-Voltage shutdown
An external voltage divider from the power source sets the
shutdown comparator levels. The comparator threshold is
2.5V. Hysteresis is set by an internal current source (20µA)
that is switched on or off as the UVLO pin potential
crosses the 2.5V threshold.
-
EP
Exposed PAD, underside of the LLP package
option
Internally bonded to the die substrate. Connect to GND
potential for low thermal impedance.
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Block Diagram
Figure 3. Simplified Block Diagram
7.6V SERIES
REGULATOR
VCC
VIN
5V
REFERENCE
VCC
REF
UVLO
UVLO
+
-
LOGIC
2.5V
ENABLE
OUTPUTS
UVLO
HYSTERESIS
(20 PA)
VCC
OUT_A
CLK
RT
DRIVER
OSCILLATOR
SYNC
SLOPE D TO VIN
DEADTIME
OR
OVERLAP
CONTROL
FF RAMP
RAMP
TIME
VCC
5V
5k
+
-
COMP
OUT_B
PWM
1V
SS Amp
(Sink Only)
LOGIC
SS
S
Q
R
Q
DRIVER
+
-
2.5V
MAX V*S
CLAMP
CS1
PGND
+
-
0.5V
CS2
0.5V
+
AGND
CLK + LEB
SS
20 PA
SS
19 PA
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.
4
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Absolute Maximum Ratings
(1)
VIN to GND
-0.3V to 105V
VCC to GND
-0.3V to 16V
CS1, CS2 to GND
-0.3 to 1.00V
All other inputs to GND
-0.3 to 7V
ESD Rating
(2)
Human Body Model
2kV
Storage Temperature Range
-55°C to 150°C
Junction Temperature
150°C
(1)
(2)
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 guaranteed specifications and test conditions, see the Electrical Characteristics.
For detailed information on soldering plastic TSSOP and LLP packages, refer to the Packaging Data Book available from National
Semiconductor Corporation.
Operating Ratings
(1)
VIN Voltage
13 to 90V
External Voltage Applied to VCC
8 to 15V
Operating Junction Temperature
-40°C to +125°C
(1)
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 guaranteed specifications and test conditions, see the Electrical Characteristics.
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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 = 31.3kΩ, RSET = 27.4kΩ) unless otherwise stated (1)
Symbol
Parameter
Conditions
Min
Typ
Max
7.3
7.6
7.9
20
25
Units
Startup Regulator
VCC Reg
VCC Regulation
VCC Current Limit
I-VIN
Startup Regulator
Leakage (external Vcc
Supply)
No Load
(2)
VIN = 100V
165
V
mA
500
µA
VCC Supply
VCC Under-voltage
Lockout Voltage (positive
going Vcc)
VCC Under-voltage
Hysteresis
VCC Supply Current (ICC)
VCC Reg 220mV
VCC Reg 120mV
1.0
1.5
V
2.0
V
4.2
mA
5
5.15
V
25
50
mV
Cgate = 0
Reference Supply
VREF
Ref Voltage
IREF = 0 mA
4.85
Ref Voltage Regulation
IREF = 0 to 10mA
Ref Current Limit
10
20
mA
Current Limit
CS1 Prop
CS1 Delay to Output
CS1 Step from 0 to 0.6V
Time to onset of OUT
Transition (90%)
Cgate = 0
40
ns
CS2 Prop
CS2 Delay to Output
CS2 Step from 0 to 0.6V
Time to onset of OUT
Transition (90%)
Cgate = 0
50
ns
Cycle by Cycle Threshold
Voltage (CS1)
Cycle Skip Threshold
Voltage (CS2)
Resets SS capacitor; auto
restart
0.45
0.5
0.55
V
0.45
0.5
0.55
V
Leading Edge Blanking
Time (CS1)
50
ns
CS1 Sink Impedance
(clocked)
CS1 = 0.4V
30
50
Ω
CS1 Sink Impedance
(Post Fault Discharge)
CS1 = 0.6V
15
30
Ω
CS2 Sink Impedance
(Post Fault Discharge)
CS2 = 0.6V
55
95
Ω
CS1 and CS2 Leakage
Current
CS = CS Threshold - 100mV
1
µA
Soft-Start
Soft-start Current Source
Normal
17
22
27
µA
Soft-start Current Source
following a CS2 event
0.5
1
1.5
µA
Oscillator
(1)
(2)
6
Frequency1
TA = 25°C
TJ = Tlow to Thigh
180
175
200
220
225
kHz
Frequency2
RT = 10.4KΩ
510
580
650
kHz
All limits are guaranteed. All electrical characteristics having room temperature limits are tested during production with TA = TJ = 25°C.
All hot and cold limits are guaranteed by correlating the electrical characteristics to process and temperature variations and applying
statistical process control.
Device thermal limitations may limit usable range.
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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. VIN = 48V, VCC = 10V, RT = 31.3kΩ, RSET = 27.4kΩ) unless otherwise stated (1)
Symbol
Parameter
Conditions
Min
Sync threshold
Typ
Max
Units
2
Min Sync Pulse Width
V
100
Sync Frequency Range
160
ns
kHz
PWM Comparator
Delay to Output
COMP step 5V to 0V
Time to onset of OUT_A
transition low
Duty Cycle Range
40
0
COMP to PWM Offset
0.7
COMP Open Circuit
Voltage
4.3
COMP Short Circuit
Current
1
ns
80
%
1.3
V
5.9
V
COMP = 0V
0.6
1
1.4
mA
Delta RAMP measured from
onset of OUT_A to Ramp peak.
COMP = 5V
2.4
2.5
2.6
V
Undervoltage Shutdown
Threshold
2.44
2.5
2.56
V
Undervoltage Shutdown
Hysteresis
16
20
24
µA
5
10
Ω
Volt x Second Clamp
Ramp Clamp Level
UVLO Shutdown
Output Section
OUT_A High Saturation
MOS Device @ Iout = -10mA,
OUTPUT_A Peak Current Bipolar Device @ Vcc/2
Sink
3
A
Ω
OUT_A Low Saturation
MOS Device @ Iout = 10mA,
6
OUTPUT_A Rise Time
Cgate = 2.2nF
20
9
ns
OUTPUT_A Fall Time
Cgate = 2.2nF
15
ns
OUT_B High Saturation
MOS Device @ Iout = -10mA,
10
Ω
20
OUTPUT_B Peak Current Bipolar Device @ Vcc/2
Sink
1
A
OUT_B Low Saturation
MOS Device @ Iout = 10mA,
12
OUTPUT_B Rise Time
Cgate = 1nF
20
ns
OUTPUT_B Fall Time
Cgate = 1nF
15
ns
Ω
18
Output Timing Control
Overlap Time
RSET = 38 kΩ connected to
GND, 50% to 50% transitions
75
105
135
ns
Deadtime
RSET = 29.5 kΩ connected to
REF, 50% to 50% transitions
75
105
135
ns
Thermal Shutdown
TSD
Thermal Shutdown
Threshold
165
°C
Thermal Shutdown
Hysteresis
25
°C
MTC Package
125
°C/W
SDA Package
32
°C/W
Thermal Resistance
θJA
Junction to Ambient
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Typical Performance Characteristics
VCC Regulator Start-up Characteristics, VCC
vs
Vin
VCC
vs
ICC
16
10
VIN
14
8
12
6
VCC (V)
VCC (V)
10
VCC
8
4
6
4
2
2
0
0
0
2
4
6
8
10
12
14
16
0
5
10
15
20
VIN (V)
ICC (mA)
VREF
vs
IREF
Oscillator Frequency
vs
RT
25
6
5
VREF (V)
4
3
2
1
0
0
5
10
15
20
25
IREF (mA)
Overlap Time
vs
Temperature
RSET = 38K
Overlap Time
vs
RSET
400
140
130
300
OVERLAP TIME (ns)
OVERLAP TIME (ns)
350
250
200
150
100
120
110
100
90
50
0
0
20
40
60
80
100
120
RSET (k:)
8
80
-40
25
_
75
_
125
o
TEMPERATURE ( C)
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Typical Performance Characteristics (continued)
Dead Time
vs
Temperature
RSET = 29.5K
Dead Time
vs
RSET
140
400
350
130
DEADTIME (ns)
DEADTIME (ns)
300
250
200
150
120
110
100
100
90
50
0
0
20
40
60
80
100
80
-40
120
RSET (k:)
25
75
125
o
TEMPERATURE ( C)
SS Pin Current
vs
Temperature
26
SS CURRENT (PA)
24
22
20
18
16
14
-40
25
75
125
o
TEMPERATURE ( C)
Detailed Operating Description
The LM5025A is a functional variant of the LM5025 active clamp PWM controller. The functional differences of
the LM5025A are:
The CS1 and CS2 current limit thresholds have been increased to 0.5V.
The internal CS2 filter discharge device has been disabled and no longer operates each clock cycle.
The internal VCC and VREF regulators continue to operate when the line UVLO pin is below threshold.
The LM5025A PWM controller contains all of the features necessary to implement power converters utilizing the
Active Clamp Reset technique. The device can be configured to control either a P-Channel clamp switch or an NChannel clamp switch. With the active clamp technique higher efficiencies and greater power densities can be
realized compared to conventional catch winding or RDC clamp / reset techniques. Two control outputs are
provided, the main power switch control (OUT_A) and the active clamp switch control (OUT_B). The active clamp
output can be configured for either a guaranteed overlap time (for P-Channel switch applications) or a
guaranteed dead time (for N_Channel applications). The two internal compound gate drivers parallel both MOS
and Bipolar devices, providing superior gate drive characteristics. This controller is designed for high-speed
operation including an oscillator frequency range up to 1MHz and total PWM and current sense propagation
delays less than 100ns. The LM5025A includes a high-voltage start-up regulator that operates over a wide input
range of 13V to 90V. Additional features include: Line Under Voltage Lockout (UVLO), softstart, oscillator
UP/DOWN sync capability, precision reference and thermal shutdown.
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High Voltage Start-Up Regulator
The LM5025A contains an internal high voltage start-up regulator that allows the input pin (VIN) to be connected
directly to the line voltage. The regulator output is internally current limited to 20mA. 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 100µF. When the voltage on the VCC pin reaches the
regulation point of 7.6V and the internal voltage reference (REF) reaches its regulation point of 5V, the controller
outputs are enabled. The outputs will remain enabled until VCC falls below 6.2V or the line Under Voltage Lock
Out detector indicates that VIN is out of range. In typical applications, an auxiliary transformer winding is
connected through a diode to the VCC pin. This winding must raise the VCC voltage above 8V to shut off the
internal start-up regulator. Powering VCC from an auxiliary winding improves efficiency while reducing the
controller power dissipation.
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 regulator 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 LM5025A contains a line Under Voltage Lock Out (UVLO) circuit. An external set-point voltage divider from
Vin to GND, 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 undervoltage threshold
is not met, both outputs are disabled,all other functions of the controller remain active. UVLO hysteresis is
accomplished with an internal 20uA 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 voltage 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. Pulling the UVLO pin below the 2.5V threshold disables the PWM outputs.
PWM Outputs
The relative phase of the main (OUT_A) and active clamp outputs (OUT_B) can be configured for the specific
application. For active clamp configurations utilizing a ground referenced P-Channel clamp switch, the two
outputs should be in phase with the active clamp output overlapping the main output. For active clamp
configurations utilizing a high side N-Channel switch, the active clamp output should be out of phase with main
output and there should be a dead time between the two gate drive pulses. A distinguishing feature of the
LM5025A is the ability to accurately configure either dead time (both off) or overlap time (both on) of the gate
driver outputs. The overlap / deadtime magnitude is controlled by the resistor value connected to the TIME pin of
the controller. The opposite end of the resistor can be connected to either REF for deadtime control or GND for
overlap control. The internal configuration detector senses the connection and configures the phase relationship
of the main and active clamp outputs. The magnitude of the overlap/dead time can be calculated as follows:
Overlap Time (ns) = 2.8 x RSET - 1.2
Dead Time (ns) = 2.9 x RSET +20
RSET in kΩ, Time in ns
OUT_A
P-Channel Active Clamp
(RSET to GND)
K1 * RSET
K1 * RSET
OUT_B
OUT_A
N-Channel Active Clamp
(RSET to REF)
K2 * RSET
K2 * RSET
OUT_B
10
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Compound Gate Drivers
The LM5025A contains two unique compound gate drivers, which parallel both MOS and Bipolar devices to
provide high drive current throughout the entire switching event. The Bipolar device provides most of the drive
current capability and provides a relatively constant sink current which is ideal for driving large power MOSFETs.
As the switching event nears conclusion and the Bipolar device saturates, the internal MOS device continues to
provide a low impedance to compete the switching event.
During turn-off at the Miller plateau region, typically around 2V - 3V, is where gate driver current capability is
needed most. The resistive characteristics of all MOS gate drivers are adequate for turn-on since the supply to
output voltage differential is fairly large at the Miller region. During turn-off however, the voltage differential is
small and the current source characteristic of the Bipolar gate driver is beneficial to provide fast drive capability.
VCC
OUT
CNTRL
PGND
PWM Comparator
The PWM comparator compares the ramp signal (RAMP) to the loop error signal (COMP). This comparator is
optimized for speed in order to achieve minimum controllable duty cycles. The internal 5kΩ pull-up resistor,
connected between the internal 5V reference and COMP, can be used as the pull-up for an optocoupler. The
comparator polarity is such that 0V on the COMP pin will produce a zero duty cycle on both gate driver outputs.
Volt Second Clamp
The Volt x Second Clamp comparator compares the ramp signal (RAMP) to a fixed 2.5V reference. By proper
selection of RFF and CFF, the maximum ON time of the main switch can be set to the desired duration. The ON
time set by Volt x Second Clamp varies inversely with the line voltage because the RAMP capacitor is charged
by a resistor connected to Vin while the threshold of the clamp is a fixed voltage (2.5V). An example will illustrate
the use of the Volt x Second Clamp comparator to achieve a 50% duty cycle limit, at 200KHz, at a 48V line input:
A 50% duty cycle at a 200KHz requires a 2.5µs of ON time. At 48V input the Volt x Second product is 120V x µs
(48V x 2.5µs). To achieve this clamp level:
RFF x CFF = VIN x TON / 2.5V
48 x 2.5µ / 2.5 = 48µ
(1)
(2)
Select CFF = 470pF
RFF = 102kΩ
The recommended capacitor value range for CFF is 100pF to 1000pF.
The CFF ramp capacitor is discharged at the conclusion of every cycle by an internal discharge switch controlled
by either the internal clock or by the V x S Clamp comparator, whichever event occurs first.
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Current Limit
The LM5025A contains two modes of over-current protection. If the sense voltage at the CS1 input exceeds 0.5V
the present power cycle is terminated (cycle-by-cycle current limit). If the sense voltage at the CS2 input exceeds
0.5V, the controller will terminate the present cycle, discharge the softstart capacitor and reduce the softstart
current source to 1µA. The softstart (SS) capacitor is released after being fully discharged and slowly charges
with a 1µA current source. When the voltage at the SS pin reaches approximately 1V, the PWM comparator will
produce the first output pulse at OUT_A. After the first pulse occurs, the softstart current source will revert to the
normal 20µA level. Fully discharging and then slowly charging the SS capacitor protects a continuously overloaded converter with a low duty cycle hiccup mode.
These two modes of over-current protection allow the user great flexibility to configure the system behavior in
over-load conditions. If it is desired for the system to act as a current source during an over-load, then the CS1
cycle-by-cycle current limiting should be used. In this case the current sense signal should be applied to the CS1
input and the CS2 input should be grounded. If during an overload condition it is desired for the system to briefly
shutdown, followed by softstart retry, then the CS2 hiccup current limiting mode should be used. In this case the
current sense signal should be applied to the CS2 input and the CS1 input should be grounded. This shutdown /
soft-start retry will repeat indefinitely while the over-load condition remains. The hiccup mode will greatly reduce
the thermal stresses to the system during heavy overloads. The cycle-by-cycle mode will have higher system
thermal dissipations during heavy overloads, but provides the advantage of continuous operation for short
duration overload conditions.
It is possible to utilize both over-current modes concurrently, whereby slight overload conditions activate the CS1
cycle-by-cycle mode while more severe overloading activates the CS2 hiccup mode. Generally the CS1 input will
always be configured to monitor the main switch FET current each cycle. The CS2 input can be configured in
several different ways depending upon the system requirements.
a) The CS2 input can also be set to monitor the main switch FET current except scaled to a higher threshold
than CS1
b) An external over-current timer can be configured which trips after a pre-determined over-current time, driving
the CS2 input high, initiating a hiccup event.
c) In a closed loop voltage regulaton system, the COMP input will rise to saturation when the cycle-by-cycle
current limit is active. An external filter/delay timer and voltage divider can be configured between the COMP pin
and the CS2 pin to scale and delay the COMP voltage. If the CS2 pin voltage reaches 0.5V a hiccup event will
initiate.
A small RC filter, located near the controller, is recommended for each of the CS pins. The CS1 input has an
internal FET which discharges the current sense filter capacitor at the conclusion of every cycle, to improve
dynamic performance. This same FET remains on an additional 50ns at the start of each main switch cycle to
attenuate the leading edge spike in the current sense signal. The CS2 discharge FET only operates following a
CS2 event, UVLO and thermal shutdown.
The LM5025A CS 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 very close to the device and connected directly to the pins of the IC (CS and GND). If a
current sense transformer is used, both leads of the transformer secondary should be routed to the filter
network , which should be located close to the IC. If a sense resistor in the source of the main switch MOSFET is
used for current sensing, a low inductance type of resistor is required. When designing with a current sense
resistor, all of the noise sensitive low power ground connections should be connected together near the IC GND
and a single connection should be made to the power ground (sense resistor ground point).
CS2
SS
12
20 PA
1 PA
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Product Folder Links: LM5025A
LM5025A
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SNVS293D – DECEMBER 2004 – REVISED MARCH 2010
Oscillator and Sync Capability
The LM5025A 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 = (5725/F)1.026
(3)
where F is in kHz and RT in kΩ.
The RT resistor should be located very close to the device and connected directly to the pins of the IC (RT and
GND).
A unique feature of LM5025A is the ability to synchronize the oscillator to an external clock with a frequency that
is either higher or lower than the frequency of the internal oscillator. The lower frequency sync frequency range is
80% of the free running internal oscillator frequency. There is no constraint on the maximum SYNC frequency. A
minimum pulse width of 100ns is required for the synchronization clock . If the synchronization feature is not
required, the SYNC pin should be connected to GND to prevent any abnormal interference . The internal
oscillator can be completely disabled by connecting the RT pin to REF. Once disabled, the sync signal will act
directly as the master clock for the controller. Both the frequency and the maximum duty cycle of the PWM
controller can be controlled by the SYNC signal (within the limitations of the Volt x Second Clamp). The
maximum duty cycle (D) will be (1-D) of the SYNC signal.
Feed-Forward Ramp
An external resistor (RFF) and capacitor (CFF) connected to VIN and GND are required to create the PWM ramp
signal. The slope of the signal at the RAMP pin will vary in proportion to the input line voltage. This varying slope
provides line feedforward information necessary to improve line transient response with voltage mode control.
The RAMP signal is compared to the error signal at the COMP pin by the pulse width modulator comparator to
control the duty cycle of the main switch output. The Volt Second Clamp comparator also monitors the RAMP pin
and if the ramp amplitude exceeds 2.5V the present cycle is terminated. The ramp signal is reset to GND at the
end of each cycle by either the internal clock or the Volt Second comparator, which ever occurs first.
Soft-Start
The softstart feature allows the power converter to gradually reach the initial steady state operating point, thus
reducing start-up stresses and surges. At power on, a 20µA current is sourced out of the softstart pin (SS) into
an external capacitor. The capacitor voltage will ramp up slowly and will limit the COMP pin voltage and therefore
the PWM duty cycle. In the event of a fault as determined by VCC undervoltage, line undervoltage (UVLO) or
second level current limit, the output gate drivers are disabled and the softstart capacitor is fully discharged.
When the fault condition is no longer present a softstart sequence will be initiated. Following a second level
current limit detection (CS2), the softstart current source is reduced to 1µA until the first output pulse is
generated by the PWM comparator. The current source returns to the nominal 20µA level after the first output
pulse (~1V at the SS pin).
Thermal Protection
Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event the maximum junction
temperature is exceeded. When activated, typically at 165°C, the controller is forced into a low power standby
state with the output drivers and the bias regulator disabled. The device will restart after the thermal hysteresis
(typically 25°C). During a restart after thermal shutdown, the softstart capacitor will be fully discharged and then
charged in the low current mode (1µA) similar to a second level current limit event. The thermal protection
feature is provided to prevent catastrophic failures from accidental device overheating.
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Product Folder Links: LM5025A
13
LM5025A
SNVS293D – DECEMBER 2004 – REVISED MARCH 2010
www.ti.com
Application Circuit: Input 36-78V, Output 3.3V, 30A
14
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Product Folder Links: LM5025A
PACKAGE OPTION ADDENDUM
www.ti.com
17-Nov-2012
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package Qty
Drawing
Eco Plan
Lead/Ball Finish
(2)
MSL Peak Temp
Samples
(3)
(Requires Login)
LM5025AMTC
ACTIVE
TSSOP
PW
16
92
TBD
CU SNPB
Level-1-260C-UNLIM
LM5025AMTC/NOPB
ACTIVE
TSSOP
PW
16
92
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
LM5025AMTCX/NOPB
ACTIVE
TSSOP
PW
16
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
LM5025ASD
ACTIVE
WSON
NHQ
16
1000
TBD
CU SNPB
Level-1-260C-UNLIM
LM5025ASD/NOPB
ACTIVE
WSON
NHQ
16
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
LM5025ASDX/NOPB
ACTIVE
WSON
NHQ
16
4500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
(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.
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
PACKAGE OPTION ADDENDUM
www.ti.com
17-Nov-2012
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
17-Nov-2012
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
LM5025AMTCX/NOPB
TSSOP
PW
16
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
LM5025ASD
WSON
NHQ
16
1000
178.0
12.4
5.3
5.3
1.3
8.0
12.0
Q1
LM5025ASD/NOPB
WSON
NHQ
16
1000
178.0
12.4
5.3
5.3
1.3
8.0
12.0
Q1
LM5025ASDX/NOPB
WSON
NHQ
16
4500
330.0
12.4
5.3
5.3
1.3
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
17-Nov-2012
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM5025AMTCX/NOPB
LM5025ASD
TSSOP
PW
16
2500
349.0
337.0
45.0
WSON
NHQ
16
1000
203.0
190.0
41.0
LM5025ASD/NOPB
WSON
NHQ
16
1000
203.0
190.0
41.0
LM5025ASDX/NOPB
WSON
NHQ
16
4500
349.0
337.0
45.0
Pack Materials-Page 2
MECHANICAL DATA
NHQ0016A
SDA16A (Rev A)
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