LM5007_08 [NSC]
High Voltage (80V) Step Down Switching Regulator; 高电压（ 80V ）降压开关稳压器
| 型号： | LM5007_08 |
| 厂家： | 
National Semiconductor |
| 描述： | High Voltage (80V) Step Down Switching Regulator |
| 文件： | 总12页 (文件大小：281K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
February 5, 2008
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 provid-
ing 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.
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
Non-Isolated Buck Regulator
■
■
■
Secondary High Voltage Post Regulator
+42V Automotive Systems
Package
MSOP - 8
■
■
LLP - 8 (4mm x 4mm)
Connection Diagram
20078302
8-Lead MSOP, LLP
Ordering Information
Order Number
LM5007MM
LM5007MMX
LM5007SD
Package Type
MSOP-8
MSOP-8
LLP-8
NSC Package Drawing
MUA08A
Supplied As
1000 Units on Tape and Reel
3500 Units on Tape and Reel
1000 Units on Tape and Reel
4500 Units on Tape and Reel
MUA08A
SDC08A
LM5007SDX
LLP-8
SDC08A
© 2008 National Semiconductor Corporation
200783
www.national.com
Typical Application Circuit and Block Diagram
20078301
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2
Pin Descriptions
Pin
1
Name
SW
Description
Application Information
Switching Node
Power switching node. Connect to the LC output filter.
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
5
RTN
FB
Circuit Ground
Feedback Signal from Regulated Output
This pin is connected to the inverting input of the
internal regulation comparator. The regulation
threshold is 2.5V.
6
7
RON
Vcc
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.
Output from the internal high voltage bias regulator. If an auxiliary voltage is available to raise the voltage
VCC is nominally regulated to 7 Volts
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
EP
Input supply voltage
Recommended operating range: 9V to 75V.
Exposed PAD, underside of the LLP package
option
Internally bonded to the die substrate. Connect to
GND potential for low thermal impedance.
3
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BST to VCC
80V
Absolute Maximum Ratings (Note 1)
BST to SW
VCC to GND
14V
14V
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
All Other Inputs to GND
Lead Temperature (Soldering 4 sec)
Storage Temperature Range
-0.3 to 7V
260°C
-55°C to +150°C
VIN to GND
80V
94V
-1V
BST to GND
SW to GND (Steady State)
ESD Rating (Note 5)
Human Body Model
Machine Model
Operating Ratings (Note 1)
VIN
9V to 75V
−40°C to + 125°C
2kV
200V
Junction Temperature
Electrical Characteristics
Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction Tem-
perature range. VIN = 48V, unless otherwise stated (Note 3).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Startup Regulator
VCC Reg
VCC Regulator Output
VCC Current Limit
6.6
7
7.4
V
(Note 4)
11
mA
VCC Supply
VCC undervoltage Lockout
Voltage (VCC increasing)
6.3
V
VCC Undervoltage Hysteresis
VCC UVLO Delay (filter)
206
3
mV
µs
Operating Current (ICC)
Shutdown/Standby Current
Non-Switching, FB = 3V
RON = 0V
500
100
675
200
µA
µA
Switch Characteristics
Buck Switch Rds(on)
ITEST = 200mA,
VBST −VSW = 6.3V
(Note 6)
0.74
1.34
5.5
Ω
Gate Drive UVLO (VBST – VSW) Rising
Gate Drive UVLO Hysteresis
3.4
4.5
V
mV
V
400
Breakdown Voltage
VIN to Ground
TJ = 25°C
80
76
TJ = -40°C to +125°C
Breakdown Voltage
BST to VCC
TJ = 25°C
80
76
V
TJ = -40°C to +125°C
Current Limit
Current Limit Threshold
535
725
225
900
mA
ns
Current Limit Response Time
Iswitch Overdrive = 0.1A Time
to Switch Off
OFF time generator (test 1)
OFF time generator (test 2)
FB=0V, RCL = 100K
FB=2.3V, RCL = 100K
17
µs
µs
2.65
On Time Generator
TON -1
Vin = 10V
Ron = 200K
2.15
290
2.77
390
3.5
490
1.1
µs
ns
TON -2
Vin = 75V
Ron = 200K
Remote Shutdown Threshold
Remote Shutdown Hysteresis
Rising
0.45
0.7
40
V
mV
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Symbol
Parameter
Conditions
FB = 0V
Min
Typ
300
2.5
Max
Units
ns
Minimum Off Time
Minimum Off Timer
Regulation and OV Comparators
FB Reference Threshold
Internal reference
2.445
2.550
V
Trip point for switch ON
FB Over-Voltage Threshold
FB Bias Current
Trip point for switch OFF
2.875
100
V
nA
Thermal Shutdown
Tsd
Thermal Shutdown Temp.
165
25
°C
°C
Thermal Shutdown Hysteresis
Thermal Resistance
Junction to Ambient
MUA Package
SDC Package
°C/W
°C/W
θJA
200
40
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.
5
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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 discontinu-
ous mode frequency and remains relatively constant with load
and line variations. The approximate continuous mode oper-
ating 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 provid-
ing 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 propor-
tional to Vout. This current limiting scheme reduces load
current foldback. Additional protection features include: Ther-
mal Shutdown, Vcc undervoltage lockout, Gate drive under-
voltage 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.
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 feedback comparator in hysteretic regulators depend up-
on 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 Equiva-
lent 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.
Hysteretic Control Circuit Overview
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 be-
low the reference voltage, the buck switch is turned on for a
fixed time pulse determined by the line voltage and a pro-
gramming 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.
For applications where lower output voltage ripple is required
the load can be connected directly to the low ESR output ca-
pacitor, 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 par-
allel 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 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 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 fre-
quency 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 cur-
rent and switching frequency. The approximate discontinuous
mode operating frequency can be calculated as follows:
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.
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6
20078305
FIGURE 1. Low Ripple Output Configuration
20078306
FIGURE 2. Self Biased Configuration
Over-Voltage Comparator
ON Time generator and Shutdown
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 over-voltage com-
parator monitors the FB pin versus an internal 2.875V refer-
ence (OV_REF). If the voltage at FB rises above OV_REF the
comparator immediately terminates the buck switch on time
pulse.
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 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 :
7
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Ton = 1.42 x 10-10 x RON / VIN
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 re-
sistor.
The RON pin of the LM5007 also provides a shutdown function
which disables the regulator and significantly decreases qui-
escent power dissipation. By pulling the RON pin to below 0.7V
20078307
FIGURE 3. Shutdown Implementation
itor 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.
Current Limit
The LM5007 contains an intelligent current limit off timer in-
tended 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 immedi-
ately 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.
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 in-
ternal 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 re-circulating diode
must be greater than the maximum line input voltage.
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 fol-
lowing equation:
Thermal Protection
Internal Thermal Shutdown circuitry is provided to protect the
integrated circuit in the event the maximum junction temper-
ature 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 fea-
ture is provided to prevent catastrophic failures from acciden-
tal device overheating.
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, out-
put resistance or a larger voltage drop rectifier may be nec-
essary to balance the inductor cycle volt*time product and
limit the short circuit current.
Minimum Load Current
A minimum load current of 1 mA is required to maintain proper
operation. If the load current falls below that level, the boot-
strap capacitor may discharge during the long off-time, and
the circuit will either shutdown, or cycle on and off at a low
frequency. If the load current is expected to drop below 1 mA
in the application, the feedback resistors should be chosen
low enough in value so they provide the minimum required
current at nominal Vout.
N - Channel Buck Switch and Driver
The LM5007 integrates an N-Channel Buck switch and as-
sociated floating high voltage gate driver. This gate driver
circuit works in conjunction with an external bootstrap capac-
itor and an internal high voltage diode. The bootstrap capac-
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8
Operational Waveforms
LM5007 10V Output Efficiency
20078308
LM5007 Operation: VOUT = 10V, VIN = 20V, IOUT = 250mA
CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current
FIGURE 4.
20078310
FIGURE 6.
Operational Waveforms
Current Limit VFB vs TOFF
RCL = 50k -600k
20078309
LM5007 Operation: VOUT = 10V, VIN = 75V, IOUT = 250mA
CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current
FIGURE 5.
20078311
FIGURE 7.
9
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20078312
FIGURE 8. VIN vs TON
RON = 100k, 200k, 300k
10V, 400mA Demo Board Bill of Materials
ITEM
C1
C2
C3
C4
C5
D1
L1
PART NUMBER
C4532X7R2A105M
C4532X7R1E156M
C1206C104K5RAC
C1206C103K5RAC
C3216X7R2A104KT
MURA110T3
DESCRIPTION
CAPACITOR, CER, TDK
CAPACITOR, CER, TDK
CAPACITOR, CER, KEMET
CAPACITOR, CER, KEMET
CAPACITOR, CER, TDK
DIODE, 100V, ON SEMI
BUCK INDUCTOR, TDK
RESISTOR
VALUE
1µ, 100V
15µ, 25V
0.1µ, 50V
0.01µ, 50V
0.1µ, 100V
SLF7045T-101MR60-1
CRCW12062003F
CRCW12061003F
CRCW12063011F
CRCW12061001F
CRCW12061R00F
LM5007
100µH
200K
100K
3.01K
1K
R1
R2
R3
R4
R5
U1
RESISTOR
RESISTOR
RESISTOR
RESISTOR
1
REGULATOR, NATIONAL
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10
Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead MSOP Package
NS Package Number MUA08A
8-Lead LLP Package
NS Package Number SDC08A
11
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