LM5007
High Voltage (80V) Step Down Switching Regulator
General 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 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
V
IN
. 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 intelli-
gent current limit is implemented in the LM5007 with forced
off time that is inversely proportional to V
OUT
. This current
limiting scheme reduces load current foldback. Additional
protection features include: Thermal Shutdown, Vcc under-
voltage lockout, gate drive undervoltage lockout, and Max
Duty Cycle limiter.
Features
n
Integrated 80V, 0.7A N-Channel Buck Switch
n
Internal HV Vcc Regulator
n
No Control Loop Compensation Required
n
Ultra-Fast Transient Response
n
On Time Varies Inversely with Line Voltage
n
Operating Frequency Nearly Constant with Varying Line
Voltage
n
Adjustable Output Voltage
n
Highly Efficient Operation
n
Precision Reference
n
Low Bias Current
n
Intelligent Current Limit Protection
n
Thermal Shutdown
n
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
January 2004
LM5007
High
V
oltage
(80V)
Step
Down
Switching
Regulator
2004 National Semiconductor Corporation
DS200783
www.national.com
Typical Application Circuit and Block Diagram
20078301
LM5007
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2
Pin Description
PIN
NAME
DESCRIPTION
APPLICATION INFORMATION
1
SW
Switching Node
Power switching node. Connect to the LC output
filter.
2
BST
Boost Bootstrap 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
R
CL
Current Limit OFF time programming pin
Toff = 10
-5
/ (0.59 + (FB / 7.22 x 10
- 6
x R
CL
))
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
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
R
ON
On time set pin
Ton = 1.42 x 10
-10
R
ON
/ 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. V
CC
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
LM5007
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3
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
IN
to GND
80V
BST to GND
94V
SW to GND (Steady State)
-1V
ESD Rating (Note 5)
Human Body Model
2kV
Machine Model
200V
BST to V
CC
80V
BST to SW
14V
V
CC
to GND
14V
All Other Inputs to GND
-0.3 to 7V
Lead Temperature (Soldering 4 sec)
260C
Storage Temperature Range
-55C to +150C
Operating Ratings
(Note 1)
V
IN
9V to 75V
Junction Temperature
-40C to + 125C
Electrical Characteristics
Specifications with standard typeface are for T
J
= 25C, and those with boldface type apply over full Operating Junction
Temperature range. V
IN
= 48V, unless otherwise stated (Note 3).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Startup Regulator
V
CC
Reg
V
CC
Regulator Output
6.6
7
7.4
V
V
CC
Current Limit
(Note 4)
11
mA
V
CC
Supply
V
CC
undervoltage Lockout
Voltage (V
CC
increasing)
6.3
V
V
CC
Undervoltage Hysteresis
206
mV
V
CC
UVLO Delay (filter)
3
s
Operating Current (ICC)
Non-Switching, FB = 3V
500
675
A
Shutdown/Standby Current
R
ON
= 0V
100
200
A
Switch Characteristics
Buck Switch Rds(on)
I
TEST
= 200mA,
VBST -VSW = 6.3V
(Note 6)
0.74
1.34
Gate Drive UVLO (VBST
VSW)
Rising
3.4
4.5
5.5
V
Gate Drive UVLO Hysteresis
400
mV
Breakdown Voltage
V
IN
to Ground
T
J
= 25C
T
J
= -40C to +125C
80
76
V
Breakdown Voltage
BST to V
CC
T
J
= 25C
T
J
= -40C to +125C
80
76
V
Current Limit
Current Limit Threshold
535
725
900
mA
Current Limit Response Time
I
switch
Overdrive = 0.1A
Time to Switch Off
225
ns
OFF time generator (test 1)
FB=0V, RCL = 100K
17
s
OFF time generator (test 2)
FB=2.3V, RCL = 100K
2.65
s
On Time Generator
TON -1
Vin = 10V
Ron = 200K
2.15
2.77
3.5
s
TON -2
Vin = 75V
Ron = 200K
290
390
490
ns
Remote Shutdown Threshold
Rising
0.45
0.7
1.1
V
Remote Shutdown Hysteresis
40
mV
LM5007
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4
Electrical Characteristics
(Continued)
Specifications with standard typeface are for T
J
= 25C, and those with boldface type apply over full Operating Junction
Temperature range. V
IN
= 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
2.445
2.5
2.550
V
FB Over-Voltage Threshold
Trip point for switch OFF
2.875
V
FB Bias Current
100
nA
Thermal Shutdown
Tsd
Thermal Shutdown Temp.
165
C
Thermal Shutdown Hysteresis
25
C
Thermal Resistance
JA
Junction to Ambient
MUA Package
200
C/W
SDC Package
40
C/W
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 T
A
= T
J
= 25C. 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 V
CC
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 1.5k
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.
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 intelli-
gent current limit scheme is implemented in the LM5007 with
forced off time, after current limit detection, which is in-
versely 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 effi-
ciently regulate step down higher voltage inputs. This regu-
lator is well suited for 48 Volt Telcom and the new 42V
Automotive power bus ranges.
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
below the reference voltage, the buck switch is turned on for
a fixed time pulse determined by the line voltage and a
programming resistor (R
ON
). 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 fre-
quency can be relatively low and will vary with load. There-
fore at light loads the conversion efficiency is maintained,
since the switching losses decrease with the reduction in
load current and switching frequency. The approximate dis-
continuous mode operating frequency can be calculated as
follows:
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
operating frequency can be calculated as follows:
LM5007
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