NSC LM5007SD

LM5007
High Voltage (80V) Step Down Switching Regulator
General Description
Features
The LM5007 Step Down Switching Regulator features all of
the functions needed to implement low cost, efficient, Buck
bias regulators. This high voltage regulator contains an 80 V,
0.7A N-Channel Buck Switch. The device is easy to apply
and is provided in the MSOP-8 and the thermally enhanced
LLP-8 packages. The regulator is based on a hysteretic
control scheme using an on time inversely proportional to
VIN. This feature allows the operating frequency to remain
relatively constant with load and input voltage variations. The
hysteretic control requires no control loop compensation,
while providing very fast load transient response. An intelligent current limit is implemented in the LM5007 with forced
off time that is inversely proportional to VOUT. This current
limiting scheme reduces load current foldback. Additional
protection features include: Thermal Shutdown, Vcc undervoltage lockout, gate drive undervoltage lockout, and Max
Duty Cycle limiter.
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Integrated 80V, 0.7A N-Channel Buck Switch
Internal HV Vcc Regulator
No Control Loop Compensation Required
Ultra-Fast Transient Response
On Time Varies Inversely with Line Voltage
Operating Frequency Nearly Constant with Varying Line
Voltage
Adjustable Output Voltage
Highly Efficient Operation
Precision Reference
Low Bias Current
Intelligent Current Limit Protection
Thermal Shutdown
External Shutdown Control
Typical Applications
n Non-Isolated Buck Regulator
n Secondary High Voltage Post Regulator
n +42V Automotive Systems
Package
n MSOP - 8
n LLP - 8 (4mm x 4mm)
Connection Diagram
20078302
8-Lead MSOP, LLP
Ordering Information
Order Number
Package Type
NSC Package Drawing
Supplied As
LM5007MM
MSOP-8
MUA08A
1000 Units on Tape and Reel
LM5007MMX
MSOP-8
MUA08A
3500 Units on Tape and Reel
LM5007SD
LLP-8
SDC08A
Available Soon
LM5007SDX
LLP-8
SDC08A
Available Soon
© 2004 National Semiconductor Corporation
DS200783
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LM5007 High Voltage (80V) Step Down Switching Regulator
January 2004
LM5007
Typical Application Circuit and Block Diagram
20078301
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2
LM5007
Pin Description
PIN
NAME
1
SW
Switching Node
DESCRIPTION
Power switching node. Connect to the LC output
filter.
APPLICATION INFORMATION
2
BST
Boost Boot–strap capacitor input
An external capacitor is required between the BST
and the SW pins. A 0.01uF ceramic capacitor is
recommended. An internal diode between Vcc and
BST completes the Buck gate drive bias network.
3
RCL
Current Limit OFF time programming pin
Toff = 10-5 / (0.59 + (FB / 7.22 x 10− 6 x RCL))
A resistor between this pin and RTN determines the
variation of off time, along with the FB pin voltage,
per cycle while in current limit. The off time is preset
to 17uS if FB =0V and decreases as the FB pin
voltage increases.
4
RTN
Circuit Ground
5
FB
6
Feedback Signal from Regulated Output
This pin is connected to the inverting input of the
internal regulation comparator. The regulation
threshold is 2.5V.
RON
On time set pin
Ton = 1.42 x 10-10 RON / Vin
A resistor between this pin and Vin sets the switch
on time as a function of Vin. The minimum
recommended on time is 300ns at the maximum
input voltage.
7
Vcc
Output from the internal high voltage bias
regulator. VCC is nominally regulated to 7 Volts.
If an auxiliary voltage is available to raise the
voltage on this pin, above the regulation setpoint
(7V), the internal series pass regulator will
shutdown, reducing the IC power dissipation. Do not
exceed 14V. This output provides gate drive power
for the internal Buck switch. An internal diode is
provided between this pin and the BST pin. A local
0.1uF decoupling capacitor is recommended. Series
pass regulator is current limited to 10mA.
8
Vin
Input supply voltage
Recommended operating range: 9V to 75V
3
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LM5007
Absolute Maximum Ratings (Note 1)
BST to SW
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VCC to GND
14V
All Other Inputs to GND
-0.3 to 7V
Lead Temperature (Soldering 4 sec)
260˚C
VIN to GND
Storage Temperature Range
-55˚C to +150˚C
80V
14V
BST to GND
94V
SW to GND (Steady State)
-1V
Operating Ratings (Note 1)
2kV
VIN
200V
Junction Temperature
ESD Rating (Note 5)
Human Body Model
Machine Model
BST to VCC
9V to 75V
−40˚C to + 125˚C
80V
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, unless otherwise stated (Note 3).
Symbol
Parameter
Conditions
Min
Typ
Max
7
7.4
Units
Startup Regulator
VCC Reg
VCC Regulator Output
VCC Current Limit
6.6
(Note 4)
V
11
mA
VCC undervoltage Lockout
Voltage (VCC increasing)
6.3
V
VCC Undervoltage Hysteresis
206
mV
VCC Supply
VCC UVLO Delay (filter)
3
µs
Operating Current (ICC)
Non-Switching, FB = 3V
500
675
µA
Shutdown/Standby Current
RON = 0V
100
200
µA
Buck Switch Rds(on)
ITEST = 200mA,
VBST −VSW = 6.3V
(Note 6)
0.74
1.34
Ω
Gate Drive UVLO (VBST –
VSW)
Rising
4.5
5.5
V
Switch Characteristics
3.4
Gate Drive UVLO Hysteresis
400
mV
Breakdown Voltage
VIN to Ground
TJ = 25˚C
TJ = -40˚C to +125˚C
80
76
V
Breakdown Voltage
BST to VCC
TJ = 25˚C
TJ = -40˚C to +125˚C
80
76
V
Current Limit
Current Limit Threshold
535
Current Limit Response Time
Iswitch Overdrive = 0.1A
Time to Switch Off
OFF time generator (test 1)
FB=0V, RCL = 100K
OFF time generator (test 2)
FB=2.3V, RCL = 100K
725
900
mA
225
ns
17
µs
2.65
µs
On Time Generator
TON -1
Vin = 10V
Ron = 200K
2.15
2.77
3.5
µs
TON -2
Vin = 75V
Ron = 200K
290
390
490
ns
Remote Shutdown Threshold
Rising
0.45
0.7
1.1
V
Remote Shutdown Hysteresis
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40
4
mV
(Continued)
Specifications with standard typeface are for TJ = 25˚C, and those with boldface type apply over full Operating Junction
Temperature range. VIN = 48V, unless otherwise stated (Note 3).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Minimum Off Time
Minimum Off Timer
FB = 0V
300
ns
Regulation and OV Comparators
FB Reference Threshold
Internal reference
Trip point for switch ON
FB Over-Voltage Threshold
Trip point for switch OFF
2.445
2.5
2.550
V
2.875
V
100
nA
Thermal Shutdown Temp.
165
˚C
Thermal Shutdown Hysteresis
25
˚C
MUA Package
200
˚C/W
SDC Package
40
˚C/W
FB Bias Current
Thermal Shutdown
Tsd
Thermal Resistance
θJA
Junction to Ambient
Note 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.
Note 2: For detailed information on soldering plastic MSOP and LLP packages, refer to the Packaging Data Book available from National Semiconductor
Corporation.
Note 3: 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.
Note 4: The VCC output is intended as a self bias for the internal gate drive power and control circuits. Device thermal limitations limit external loading.
Note 5: The human body model is a 100pF capacitor discharge through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly
into each pin. The machine model ESD compliance level for Pin 5 is 150V. The human body ESD compliance level for Pin 7 and 8 is 1000V.
Note 6: For devices procurred in the LLP-8 package the Rds(on) limits are guaranteed by design characterization data only.
a fixed time pulse determined by the line voltage and a
programming resistor (RON). Following the on period the
switch will remain off for at least the minimum off timer period
of 300ns. If the FB pin voltage is still below the reference
after the 300ns off time, the switch will turn on again for
another on time period. This switching behavior will continue
until the FB pin voltage reaches the reference voltage level.
The LM5007 operates in discontinuous conduction mode at
light load currents or continuous conduction mode at heavier
load currents. In discontinuous conduction mode, current
through the output inductor starts at zero and ramps up to a
peak value during the buck switch on time and then back to
zero during the off time. The inductor current remains at zero
until the next on time period starts when FB falls below the
internal reference. In discontinuous mode the operating frequency can be relatively low and will vary with load. Therefore at light loads the conversion efficiency is maintained,
since the switching losses decrease with the reduction in
load current and switching frequency. The approximate discontinuous mode operating frequency can be calculated as
follows:
Detailed Operating Description
The LM5007 Step Down Switching Regulator features all of
the functions needed to implement low cost, efficient, Buck
bias regulators. This high voltage regulator contains an 80V,
0.7A N-Channel Buck Switch. The device is easy to apply
and is provided in the MSOP-8 and the thermally enhanced
LLP-8 packages. The regulator is based on a hysteretic
control scheme using an on time inversely proportional to
Vin. This feature allows the operating frequency to remain
relatively constant with load and input voltage variations. The
hysteretic control requires no control loop compensation,
while providing very fast load transient response. An intelligent current limit scheme is implemented in the LM5007 with
forced off time, after current limit detection, which is inversely proportional to Vout. This current limiting scheme
reduces load current foldback. Additional protection features
include: Thermal Shutdown, Vcc undervoltage lockout, Gate
drive undervoltage lockout and Max Duty Cycle limiter. The
LM5007 can be applied in numerous applications to efficiently regulate step down higher voltage inputs. This regulator is well suited for 48 Volt Telcom and the new 42V
Automotive power bus ranges.
Hysteretic Control Circuit
Overview
In continuous conduction mode, current flows continuously
through the inductor and never ramps down to zero. In this
mode the operating frequency is greater than the discontinuous mode frequency and remains relatively constant with
load and line variations. The approximate continuous mode
operating frequency can be calculated as follows:
The LM5007 is a Buck DC-DC regulator that uses an on time
control scheme. The on time is programmed by an external
resistor and varies inversely with line input voltage (Vin). The
core regulation elements of the LM5007 are the feedback
comparator and the on time one-shot. The regulator output
voltage is sensed at the feedback pin (FB) and is compared
to an internal reference voltage (2.5V). If the FB signal is
below the reference voltage, the buck switch is turned on for
5
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LM5007
Electrical Characteristics
LM5007
Hysteretic Control Circuit
Overview (Continued)
output capacitor, as shown in Figure 1. The series resistor
(R) will degrade the load regulation. Another technique for
enhancing the ripple voltage at the FB pin is to place a
capacitor in parallel with the feedback divider resistor R1.
The addition of the capacitor reduces the attenuation of the
ripple voltage from the feedback divider
High Voltage Bias Regulator
The output voltage (Vout) can be programmed by two external resistors as shown in Figure 1. The regulation point can
be calculated as follows:
VOUT = 2.5 x (R1 + R2) / R2
The LM5007 contains an internal high voltage bias regulator.
The input pin (Vin) can be connected directly to line voltages
from 9 to 75 Volts. To avoid supply voltage transients due to
long lead inductances on the input pin (Vin Pin 8), it is always
recommended to connect low ESR ceramic chip capacitor
() 0.1µF) between "Vin" pin and "RTN" pin (pin 4), located
close to LM5007. The regulator is internally current limited to
10mA. Upon power up, the regulator is enabled and sources
current into an external capacitor connected to the Vcc pin.
When the voltage on the Vcc pin reaches the regulation point
of 7V, the controller output is enabled.
The feedback comparator in hysteretic regulators depend
upon the output ripple voltage to switch the output transistor
on and off at regular intervals. In order for the internal
comparator to respond quickly to changes in output voltage,
proportional to inductor current, a minimum amount of capacitor Equivalent Series Resistance (ESR) is required. A
ripple voltage of 25mV to 50mV is recommended at the
feedback pin (FB) for stable operation. In cases where the
intrinsic capacitor ESR is too small, additional series resistance may be added.
An external auxiliary supply voltage can be applied to the
Vcc pin. If the auxiliary voltage is greater than 7 Volts the
internal regulator will essentially shutoff, thus reducing internal power dissipation.
For applications where lower output voltage ripple is required the load can be connected directly to the low ESR
20078305
FIGURE 1. Low Ripple Output Configuration
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6
LM5007
High Voltage Bias Regulator
(Continued)
20078306
FIGURE 2. Self Biased Configuration
resistor and into the Ron terminal is approximately proportional to Vin and used internally to control the on timer. This
scheme of input voltage feed-forward hysteretic operation
achieves nearly constant operational frequency over varying
line and load conditions. The on time equation for the
LM5007 is :
Ton = 1.42 x 10-10 x RON / VIN
The RON pin of the LM5007 also provides a shutdown function which disables the regulator and significantly decreases
quiescent power dissipation. By pulling the RON pin to below
0.7V logic threshold activates the low power shutdown
mode. The VIN quiescent current in the shutdown mode is
approximately 100µA internal to the LM5007 plus the current
in the RON resistor.
Over-Voltage Comparator
The over-voltage comparator is provided to protect the output from overvoltage conditions due to sudden input line
voltage changes or output loading changes. The overvoltage comparator monitors the FB pin versus an internal
2.875V reference (OV_REF). If the voltage at FB rises above
OV_REF the comparator immediately terminates the buck
switch on time pulse.
ON Time generator and Shutdown
The on time of the LM5007 is set inversely proportional to
the input voltage by an external resistor connected between
Ron and Vin. The Ron terminal is a low impedance input
biased at approximately 1.5V. Thus the current through the
7
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LM5007
ON Time generator and Shutdown
(Continued)
20078307
FIGURE 3. Shutdown Implementation
capacitor is charged by VCC through the internal high voltage
diode. A 0.01uF ceramic capacitor connected between the
BST pin and SW pin is recommended.
During each cycle when the Buck switch turns off, the SW
pin is approximately 0V. When the SW pin voltage is low, the
bootstrap capacitor will be charged from Vcc through the
internal diode. The minimum off timer, set to 300ns, ensures
that there will be a minimum interval every cycle to recharge
the bootstrap capacitor.
An external re-circulating diode from the SW pin to ground is
necessary to carry the inductor current after the internal
Buck switch turns off. This external diode must be of the
Ultra-fast or Schottky type to reduce turn-on losses and
current over-shoot. The reverse voltage rating of the recirculating diode must be greater than the maximum line
input voltage.
Current Limit
The LM5007 contains an intelligent current limit off timer
intended to reduce the foldback characteristic inherent with
fixed off-time over-current protection. If the current in the
Buck switch exceeds 725mA the present cycle on time is
immediately terminated (cycle by cycle current limit). Following the termination of the cycle a non-resetable current limit
off timer is initiated. The duration of the off time is a function
of the external resistor (RCI) and the FB pin voltage. When
the FB pin voltage equals zero, the current limit off time is
internally preset to 17uS. This condition occurs in short
circuit operation when a maximum amount of off time is
required.
In cases of overload (not complete short circuit) the current
limit off time can be reduced as a function of the output
voltage (measured at the FB pin). Reducing the off time with
smaller overloads reduces the amount of foldback and also
reduces the initial start-up time. The current limit off time for
a given FB pin voltage and RCI resistor can be calculated by
the following equation:
Toff = 10-5 / (0.59 + (VFB / 7.22 x 10-6 x RCL))
Applications utilizing low resistance inductors and/or a low
voltage drop rectifier may require special evaluation at high
line, short circuit conditions. In this special case the preset
17uS (FB = 0V) off time may be insufficient to balance the
inductor volt*time product. Additional inductor resistance,
output resistance or a larger voltage drop rectifier may be
necessary to balance the inductor cycle volt*time product
and limit the short circuit current.
Thermal Protection
Internal Thermal Shutdown circuitry is provided to protect the
integrated circuit in the event the maximum junction temperature is exceeded. When thermal protection is activated,
typically at 165 degrees Celsius, the controller is forced into
a low power reset state, disabling the output driver. This
feature is provided to prevent catastrophic failures from accidental device overheating.
N - Channel Buck Switch and
Driver
The LM5007 integrates an N-Channel Buck switch and associated floating high voltage gate driver. This gate driver
circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode. The bootstrap
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8
LM5007
Operational Waveforms
Current Limit VFB vs TOFF
RCL = 50k -600k
20078308
LM5007 Operation: VOUT = 10V, VIN = 20V, IOUT = 250mA
CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current
FIGURE 4.
20078311
Operational Waveforms
FIGURE 7.
VIN vs TON
RON = 100k, 200k, 300k
20078309
LM5007 Operation: VOUT = 10V, VIN = 75V, IOUT = 250mA
CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current
FIGURE 5.
LM5007 10V Output Efficiency
20078312
FIGURE 8.
20078310
FIGURE 6.
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LM5007
10V, 400mA Demo Board Bill of Materials
ITEM
PART NUMBER
DESCRIPTION
VALUE
C1
C4532X7R2A105M
CAPACITOR, CER, TDK
1µ, 100V
C2
C4532X7R1E156M
CAPACITOR, CER, TDK
15µ, 25V
C3
C1206C104K5RAC
CAPACITOR, CER, KEMET
0.1µ, 50V
C4
C1206C103K5RAC
CAPACITOR, CER, KEMET
0.01µ, 50V
C5
C3216X7R2A104KT
CAPACITOR, CER, TDK
0.1µ, 100V
D1
MURA110T3
DIODE, 100V, ON SEMI
L1
SLF7045T-101MR60-1
BUCK INDUCTOR, TDK
100µH
R1
CRCW12062003F
RESISTOR
200K
R2
CRCW12061003F
RESISTOR
100K
R3
CRCW12063011F
RESISTOR
3.01K
R4
CRCW12061001F
RESISTOR
1K
R5
CRCW12061R00F
RESISTOR
1
U1
LM5007
REGULATOR, NATIONAL
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10
LM5007
Physical Dimensions
inches (millimeters) unless otherwise noted
8-Lead MSOP Package
NS Package Number MUA08A
11
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LM5007 High Voltage (80V) Step Down Switching Regulator
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
8-Lead LLP Package
NS Package Number SDC08A
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